US20120269987A1 - Processes and Systems for Engineering a Barrier Surface for Copper Deposition - Google Patents

Abstract

An integrated system for processing a substrate in controlled environment to enable deposition of a thin copper seed layer on a surface of a metallic barrier layer of a copper interconnect is provided. The system includes a lab-ambient transfer chamber, a vacuum transfer chamber, a vacuum process module for cleaning an exposed surface of a metal oxide of a underlying metal, a vacuum process module for depositing the metallic barrier layer, and a controlled-ambient transfer chamber filled with an inert gas, wherein at least one controlled-ambient process module is coupled to the controlled-ambient transfer chamber. In addition, the system includes an electroless copper deposition process module used to deposit the thin layer of copper seed layer on the surface of the metallic barrier layer.

Description

CLAIM OF PRIORITY
• This application claims priority as a divisional of U.S. application Ser. No. 11/514,038, titled “Processes and Systems for Engineering a Barrier Surface for Copper Deposition,” filed on Aug. 30, 2006, which claims priority to U.S. Provisional Application Ser. No. 60/686,787, titled “High Rate Electroless Plating and Integration Flow to Form Cu Interconnects,” filed on Aug. 31, 2005, and U.S. application Ser. No. 11/461,415, titled “System and Method for Forming Patterned Copper lines Through Electroless Copper Plating,” filed on Jul. 27, 2006, the disclosures of which are hereby incorporated by reference.
CROSS REFERENCE TO RELATED APPLICATION
• This application is related to U.S. patent application Ser. No. 11/513,634), entitled “Processes and Systems for Engineering a Copper Surface for Selective Metal Deposition,” and U.S. patent application Ser. No. 11/513,446, entitled “Processes and Systems for Engineering a Silicon-Type Surface For Selective Metal Deposition to Form a Metal Silicide,” both of which are filed on the same day as the instant application. The disclosure of these related applications is incorporated herein by reference in their entireties for all purposes.
BACKGROUND
• Integrated circuits use conductive interconnects to wire together the individual devices on a semiconductor substrate, or to communicate externally to the integrated circuit. Interconnect metallization for vias and trenches may include aluminum alloys and copper. Electro-migration (EM) is a well-known reliability problem for metal interconnects, caused by electrons pushing and moving metal atoms in the direction of current flow at a rate determined by the current density. Electro-migration can eventually lead to the thinning of the metal line, which can result in higher resistivity or, worst case, a metal line breakage. Fortunately, not every interconnect metal line on an IC has current moving in the same direction all the time, as it mostly does in power supply and ground lines. However, as metal lines get narrower (International Technology Roadmap for Semiconductors (ITRS) calls for a ˜0.7× reduction in the line width for every technology node), electro-migration becomes more of an issue.
• In aluminum lines, EM is a bulk phenomenon and is well controlled by the addition of small amounts of a dopant, such as copper. EM in copper lines, on the other hand, is a surface phenomenon. It can occur wherever the copper is free to move, typically at an interface where there is poor adhesion between the copper and another material. In today's dual-damascene process, this happens most often on the top of the copper line where it interfaces with what is typically a SiC diffusion barrier layer, but it can also happen at the copper/barrier interface. With each migration to the next technology node, and resulting increase in current density, the problem worsens.
• The solution to EM problems, as well as related stress voids, another common reliability problem, has been a story of process integration: optimized depositions (i.e. reducing thickness of barrier and seed layers), pre- and post-deposition wafer cleanings, surface treatments, etc., all aimed at providing homogeneous surfaces and good adhesion between layers to minimize metal atom migration and void propagation. In the dual-damascene process, trenches and holes (for contacts and vias) are etched in the dielectric, then lined with a barrier material, such as tantalum (Ta), tantalum nitride (TaN), or a combination of both films, followed by the deposition of a copper seed layer, copper electroplating, copper planarization using CMP and then deposition of a dielectric stack, such as SiC/low-k/SiC. Since an oxide readily forms on copper when copper is exposed to air, proper post-CMP cleaning and removal of the copper oxide before capping the copper with SiC is required to ensure good adhesion between copper and SiC. Removal of the copper oxide prior to the SiC deposition is essential to good EM performance and reducing resultant metal resistivity.
• Recently, capping Copper with a cobalt-alloy capping layer, such as CoWP (cobalt tungsten phosphide), CoWB (cobalt tungsten boride), or CoWBP (cobalt tungsten boro-phosphide), before the SiC dielectric barrier layer, has been shown to significantly improve electro-migration, compared to SiC over copper.FIG. 1 shows that the cobalt-alloy capping layers20,30 are deposited overcopper layers23,33 and under dielectriccapping SiC layers25,35, respectively. Ta and/or TaN barrier layers are illustrated aslayers24,34. The cobalt-alloy layers20,30 improve the adhesion betweencopper23,33 andSiC cap layers25,35. The cobalt-alloy layers20,30 can also exhibit certain copper diffusion barrier characteristics. The cobalt-alloy capping layers can be selectively deposited on copper by electroless deposition. However, the electroless deposition can be inhibited by thin copper oxide layer, which can be formed when copper is exposed to air. Further, contaminants on the copper and dielectric surfaces can cause pattern-dependent plating effects include pattern-dependent thickness of the Co alloy, as well as pattern-dependent copper line thickness loss in part due to etching during the ‘incubation’ time required to initiate the Co plating reaction. Therefore, it is important to control the processing environment to limit (or control) the growth of native copper oxide, and to remove copper oxide and organic contaminants on the copper surface and organic and metallic contaminants on the dielectric surface immediately prior to depositing the metallic capping layer, such as a cobalt-alloy. Further, to reduce pattern-dependent deposition variability, the dielectric surface must be controlled to normalize its influence across structures of different pattern densities. Engineering the metal-to-metal interface between thecopper layers23,33, between copper andbarrier layers33 and34,23 and24, and the adhesion promoting layers (or metallic capping layers), such as the cobalt-alloy layers20,20, is very critical in ensuring good interfacial adhesion and good EM performance. Further, as metal lines become narrower, physical vapor deposition (PVD) barrier and seed films form a larger part of the metal line, increase the effective resistivity, and hence current density. Thin and conformal barrier and seed layers can mitigate this trend, with atomic layer deposition (ALD) barriers (TaN, Ru or hybrid combinations) providing conformal step coverage and acceptable barrier properties, and electroless Cu process providing a conformal seed layer. Until now, however, there is no electroless Cu seed layer that can adhere to the ALD TaN barrier films produced.
• In view of the foregoing, there is a need for systems and processes that produce a metal-to-metal interface with improved electro-migration performance, low sheet resistance, and improved interfacial adhesion for copper interconnects.
SUMMARY
• Broadly speaking, the embodiments fill the need by providing improved processes and systems that produce an improved metal-to-metal interface, more specifically barrier-to-copper interface, to enhance electro-migration performance, provide lower metal resistivity, and improve metal-to-metal interfacial adhesion for copper interconnects. It should be appreciated that the present invention can be implemented in numerous ways, including as a solution, a method, a process, an apparatus, or a system. Several inventive embodiments of the present invention are described below.
• In one embodiment, a method of preparing a substrate surface of a substrate to deposit a metallic barrier layer to line a copper interconnect structure of the substrate and to deposit a thin copper seed layer on a surface of the metallic barrier layer in an integrated system to improve electromigration performance of the copper interconnect is provided. The method includes cleaning an exposed surface of a underlying metal to remove surface metal oxide in the integrated system, wherein the underlying metal is part of a underlying interconnect electrically connected to the copper interconnect. The method also includes depositing the metallic barrier layer to line the copper interconnect structure in the integrated system, wherein after depositing the metallic barrier layer, the substrate is transferred and processed in controlled environment to prevent the formation of metallic barrier oxide. The method further includes depositing the thin copper seed layer in the integrated system, and depositing a gap-fill copper layer over the thin copper seed layer in the integrated system.
• In another embodiment, a method of preparing a substrate surface of a substrate to deposit a metallic barrier layer to line a copper interconnect structure of the substrate and to selectively deposit a thin copper seed layer on a surface of the metallic barrier layer in an integrated system to improve electromigration performance of the copper interconnect is provided. The method includes cleaning an exposed surface of an underlying metal to remove surface oxide in the integrated system, wherein the underlying metal is part of a underlying interconnect, the copper interconnect is electrically connected to underlying interconnect, and depositing the metallic barrier layer to line the copper interconnect structure in the integrated system, wherein after depositing the metallic barrier layer, the substrate is transferred and processed in controlled environment to prevent the formation of metallic barrier oxide. The method also includes selectively depositing the thin copper seed layer in the integrated system, and depositing a gap-fill copper layer over the thin copper seed layer in the integrated system in the integrated system.
• The method further includes removing copper overburden and metallic barrier overburden in the integrated system, wherein removing copper overburden and metallic barrier overburden creates the planarized copper surface, and removing metal-organic complex contaminants and metal oxides from the substrate surface in the integrated system. In addition, the method includes removing organic contaminants from the substrate surface in the integrated system, and reducing the planarized copper surface that is removed of metal-organic complex contaminants, metal oxides, and organic contaminants in the integrated system. Additionally, the method includes depositing a thin layer of a cobalt-alloy material on the reduced planarized copper surface in the integrated system.
• In another embodiment, a method of preparing a metallic barrier surface of a substrate to deposit a thin copper seed layer on a surface of a metallic barrier layer of a copper interconnect structure in an integrated system to improve electromigration performance of the copper interconnect structure is provided. The method includes reducing a surface of the metallic barrier layer to convert metallic barrier oxide on the surface of the metallic barrier layer to make the surface of the metallic barrier layer to be metallic-rich in the integrated system. The method also includes depositing the thin copper seed layer in the integrated system, and depositing a gap-fill copper layer over the thin copper seed layer in the integrated system.
• In another embodiment, an integrated system for processing a substrate in controlled environment to enable deposition of a thin copper seed layer on a surface of a metallic barrier layer of a copper interconnect is provided. The system includes a lab-ambient transfer chamber capable of transferring the substrate from a substrate cassette coupled to the lab-ambient transfer chamber into the integrated system, and a vacuum transfer chamber operated under vacuum at a pressure less than 1 Torr, wherein at least one vacuum process module is coupled to the vacuum transfer chamber. The system also includes a vacuum process module for cleaning an exposed surface of a metal oxide of a underlying metal in the integrated system, wherein the underlying metal is part of a underlying interconnect, the copper interconnect is electrically connected to the underlying interconnect, wherein the vacuum process module for cleaning is one of the at least one vacuum process module coupled to the vacuum transfer chamber, and is operated under vacuum at a pressure less than 1 Torr.
• The system further includes a vacuum process module for depositing the metallic barrier layer, wherein the vacuum process module for depositing the metallic barrier layer one of the at least one vacuum process module is coupled to the vacuum transfer chamber, and is operated under vacuum at a pressure less than 1 Torr, and a controlled-ambient transfer chamber filled with an inert gas selected from a group of inert gases, wherein at least one controlled-ambient process module is coupled to the controlled-ambient transfer chamber. In addition, the system includes an electroless copper deposition process module used to deposit the thin layer of copper seed layer on the surface of the metallic barrier layer, wherein the electroless copper deposition process module is one of the at least one controlled environment process modules coupled to the controlled-ambient transfer chamber.
• In another embodiment, an integrated system for processing a substrate in controlled environment to enable selective deposition of a thin copper seed layer on a surface of a metallic barrier layer of a copper interconnect and preparing a planarized copper surface of the copper interconnect to selectively depositing a thin layer of a cobalt-alloy material in an integrated system to improve electromigration performance of the copper interconnect is provided. The system includes a lab-ambient transfer chamber capable of transferring the substrate from a substrate cassette coupled to the lab-ambient transfer chamber into the integrated system, and a vacuum transfer chamber operated under vacuum at a pressure less than 1 Torr, wherein at least one vacuum process module is coupled to the vacuum transfer chamber. The system also includes an Ar sputtering process module to clean an exposed surface of a metal oxide of a underlying metal in the integrated system, wherein the underlying metal is part of a underlying interconnect, the copper interconnect is electrically connected to the underlying interconnect, the Ar sputtering process module one of the at least one vacuum process module is coupled to the vacuum transfer chamber, and an atomic layer deposition (ALD) process module for depositing a thin first metallic barrier layer, wherein the ALD process module is one of the at least one vacuum process module coupled to the vacuum transfer chamber.
• The system further includes a PVD process chamber for depositing a thin second metallic barrier layer, wherein the PVD process module is one of the at least one vacuum process module coupled to the vacuum transfer chamber, and a hydrogen reduction process module for reducing a metal oxide or metal nitride to a metal, wherein the hydrogen reduction process module is one of the at least one vacuum process module coupled to the vacuum transfer chamber. In addition, the system includes an oxygen plasma process module for removing organic contaminants from the substrate surface, wherein the oxygen plasma process module is one of the at least one vacuum process module coupled to the vacuum transfer chamber, and a controlled-ambient transfer chamber filled with an inert gas selected from a group of inert gases, wherein at least one controlled-ambient process module is coupled to the controlled-ambient transfer chamber. Additionally, the system includes an electroless copper deposition process module used to deposit the thin layer of copper seed layer and a gap-fill copper layer on the surface of the metallic barrier layer, the electroless copper deposition process module being one of the at least one controlled-ambient process module coupled to the controlled-ambient transfer chamber.
• The system also includes an electroless cobalt-alloy deposition process module used to deposit the thin layer of the cobalt-alloy material on the prepared planarized copper surface, the electroless copper alloy deposition process module being one of the at least one controlled-ambient process module coupled to the controlled-ambient transfer chamber, and a planarizing process module used to remove a copper overburden and a barrier overburden of the copper interconnect, the planarizing process module is one of the at least one controlled-ambient process module coupled to the controlled-ambient transfer module. In addition, the system includes a wet clean process module used to remove metallic contamination on the substrate surface, the wet clean process module is one of the at least one controlled-ambient process module coupled to the controlled-ambient transfer module.
• In yet another embodiment, an integrated system for processing a substrate in controlled environment to enable deposition of a thin copper seed layer on a surface of a metallic barrier layer of a copper interconnect is provided. The system includes a lab-ambient transfer chamber capable of transferring the substrate from a substrate cassette coupled to the lab-ambient transfer chamber into the integrated system, and a vacuum transfer chamber operated under vacuum at a pressure less than 1 Torr, wherein at least one vacuum process module is coupled to the vacuum transfer chamber. The system further includes a vacuum process module for reducing the metallic barrier layer, wherein the vacuum process module for reducing the metallic barrier layer one of the at least one vacuum process module is coupled to the vacuum transfer chamber, and is operated under vacuum at a pressure less than 1 Torr. In addition, the system includes a controlled-ambient transfer chamber filled with an inert gas selected from a group of inert gases, wherein at least one controlled-ambient process module is coupled to the controlled-ambient transfer chamber, and an electroless copper deposition process module used to deposit the thin layer of copper seed layer on the surface of the metallic barrier layer, wherein the electroless copper deposition process module is one of the at least one controlled environment process modules coupled to the controlled-ambient transfer chamber.
• Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
• The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, and like reference numerals designate like structural elements.
• FIG. 1 shows an exemplary cross section interconnects.
• FIGS. 2A-2D show cross sections of an interconnect structure at various stages of interconnect processing.
• FIG. 3 shows various forms of contaminants on substrate surface after metal CMP.
• FIG. 4A shows an exemplary process flow to prepare a copper surface for electrolessly depositing a cobalt-alloy.
• FIG. 4B shows an exemplary system used to process a substrate through a process flow ofFIG. 4A.
• FIGS. 5A-5C show cross sections of an interconnect structure at various stages of interconnect processing.
• FIG. 6A shows an exemplary process flow to prepare a copper surface for electrolessly depositing a cobalt-alloy.
• FIG. 6B shows an exemplary system used to process a substrate through a process flow ofFIG. 6A.
• FIGS. 7A-7C show cross sections of an interconnect structure at various stages of interconnect processing.
• FIG. 8A shows an exemplary process flow to prepare a copper surface for electrolessly depositing a cobalt-alloy.
• FIG. 8B shows an exemplary system used to process a substrate through a process flow ofFIG. 8A.
• FIGS. 9A-9E show cross sections of a metal line structure at various stages of processing.
• FIG. 10A shows an exemplary process flow to prepare a barrier layer surface for electrolessly depositing a copper layer.
• FIG. 10B shows an exemplary system used to process a substrate through a process flow ofFIG. 10A.
• FIG. 10C shows an exemplary process flow to prepare a barrier layer surface for electrolessly depositing a copper layer.
• FIG. 10D shows an exemplary system used to process a substrate through a process flow ofFIG. 10C.
• FIG. 11A shows an exemplary process flow to prepare a barrier layer surface for electrolessly depositing a copper layer and to prepare a copper surface for electrolessly depositing a cobalt-alloy.
• FIG. 11B shows an exemplary system used to process a substrate through a process flow ofFIG. 11A.
• FIGS. 12A-12D show cross sections of an interconnect structure at various stages of processing.
• FIG. 13A shows an exemplary process flow to prepare a barrier surface for electroless copper deposition and to prepare a copper surface for electrolessly depositing a cobalt-alloy.
• FIG. 13B shows an exemplary system used to process a substrate through a process flow ofFIG. 13A.
• FIGS. 14A-14D show cross section of a gate structure at various stages of forming metal silicide.
• FIG. 15A shows an exemplary process flow to prepare exposed silicon surface to form a metal silicide.
• FIG. 15B shows an exemplary system used to process a substrate through a process flow ofFIG. 15A.
• FIG. 16 shows a schematic diagram of system integration for an integrated system with ambient-controlled processing environments.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
• Several exemplary embodiments for improved metal integration techniques that modify metal interfaces by removing interfacial metal oxide by reduction to improve electro-migration metal resistivity and interface adhesion are provided. It should be appreciated that the present invention can be implemented in numerous ways, including a process, a method, an apparatus, or a system. Several inventive embodiments of the present invention are described below. It will be apparent to those skilled in the art that the present invention may be practiced without some or all of the specific details set forth herein.
• FIG. 2A shows an exemplary cross-section of an interconnect structure(s) after being patterned by using a dual damascene process sequence. The interconnect structure(s) is on asubstrate50 and has adielectric layer100, which was previously fabricated to form ametallization line101 therein. The metallization line is typically fabricated by etching a trench into the dielectric100 and then filling the trench with a conductive material, such as copper.
• In the trench, there is abarrier layer120, used to prevent thecopper material122, from diffusing into the dielectric100. Thebarrier layer120 can be made of PVD tantalum nitride (TaN), PVD tantalum (Ta), ALD TaN, or a combination of these films. Other barrier layer materials can also be used. Abarrier layer102 is deposited over theplanarized copper material122 to protect thecopper material122 from premature oxidation when viaholes114 are etched through overlyingdielectric materials104,106 to thebarrier layer102. Thebarrier layer102 is also configured to function as a selective etch stop and a copper diffusion barrier.Exemplary barrier layer102 materials include silicon nitride (SiN) or silicon carbide (SiC).
• A viadielectric layer104 is deposited over thebarrier layer102. The viadielectric layer104 can be made of an organo-silicate glass (OS G, carbon-doped silicon oxide) or other types of dielectric materials, preferably with low dielectric constants. Exemplary silicon dioxides can include, a PECVD un-doped TEOS silicon dioxide, a PECVD fluorinated silica glass (FSG), a HDP FSG, OSG, porous OSG, etc. and the like. Commercially available dielectric materials including Black Diamond (I) and Black Diamond (II) by Applied Materials of Santa Clara, Calif., Coral by Novellus Systems of San Jose, Aurora by ASM America Inc. of Phoenix, Ariz., can also be used. Over the viadielectric layer104 is atrench dielectric layer106. Thetrench dielectric layer106 may be a low K dielectric material, such as a carbon-doped oxide (C-oxide). The dielectric constant of the low K dielectric material can be about 3.0 or lower. In one embodiment, both the via and trench dielectric layers are made of the same material, and deposited at the same time to form a continuous film. After thetrench dielectric layer106 is deposited, thesubstrate50 that holds the structure(s) undergoes patterning and etching processes to form the vias holes114 andtrenches116 by known art.
• FIG. 2B shows that after the formation ofvias holes114 andtrenches116, abarrier layer130 and acopper layer132 are deposited to line and fill the via holes114 and thetrenches116. Thebarrier layer130 can be made of tantalum nitride (TaN), tantalum (Ta), Ruthenium (Ru), or a hybrid combination of these films. While these are the commonly considered materials, other barrier layer materials can also be used. Acopper film132 is then deposited to fill the via holes114 and thetrenches116.
• Aftercopper film132 fills the via holes114 andtrenches116,substrate50 is planarized by chemical-mechanical polishing (CMP) to remove the copper material (or copper overburden) and barrier layer (or barrier overburden) over the surface ofdielectric106, as shown inFIG. 2C. The next step is to cap thecopper surface140 with a copper/SiC interfaceadhesion promoter layer135, such as a cobalt-alloy, as shown inFIG. 2D. Examples of the cobalt-alloy include: CoWP, CoWB, or CoWBP, which can be selectively deposited over copper by an electroless process. The thickness of the adhesion-promoting layer can be as thin as a monolayer, which is only a few angstroms, such as 5 angstroms, to a thicker layer, such as 200 to 300 angstroms, which could also serve as a Cu diffusion barrier, eliminating the need for a dielectric cap.
• Chemical-mechanical polishing (CMP) of copper often uses benzotrizole (BTA) as a copper corrosion inhibitor. Copper forms Cu-BTA complexes with BTA. A substrate that has been processed through Cu CMP and post-CMP clean can contain copper residues in the form of a Cu-BTA complex, which is illustrated as open circles inFIG. 3, on both the Cu lines and the adjacent dielectric. Cu-BTA complexes on the dielectric need to be removed to prevent increased current leakage or metal shorting. Further, residues of Ta or other barrier material, which is illustrated as open triangles inFIG. 3, may be present in small amounts, in addition to various organic contaminants, which are illustrated as filled circles inFIG. 3. In addition to these contaminants, there are various oxides of the metals present, primarily CuO and CuO₂, which are illustrated as filled triangles inFIG. 3. Cu-BTA complexes metal oxides, and organic contaminants are three major surface contaminants that must be removed from the substrate surface. Preparing a dielectric surface and a metal surface that are free of organics and metal-containing compound contaminants is challenging and requires multiple surface preparation steps that could include both wet and dry processes.
• Following are several exemplary process flows and systems that provide surface preparation of an underlying metal to allow an over-laying metal layer to be deposited on top with good adhesion properties between the two metal layers. The metal layers deposited by the exemplary process flows and systems would exhibit improved EM performance and thus an overall lower metal resistivity.
1. Engineering Copper Surface for Cobalt-Alloy DepositionCase I: Metal CMP Stops on Dielectric Layer
• FIG. 4A shows an embodiment of a process flow of surface preparation for electrolessly depositing a cobalt-alloy over apost-CMP copper surface140 of the dual-damascene via-trench structure shown inFIG. 2C. The substrate(s) used in theprocess flow400 ofFIG. 4A have just finished metal CMP processing(s) to remove copper and bather overburden layers, such as Ta and/or TaN. As described above in the paragraph related toFIG. 3, there are various metallic and organic contaminants on the substrate surface.
• The process starts atstep401 by removing metal-organic complex contaminants (or complexed metal-organic contaminants), such as Cu-BTA complex, and metal oxides from the substrate surface. Although metal contaminants will be removed from both the copper and dielectric surfaces, the purpose of this step is to enhance selectivity and improve the Co film morphology by eliminating potential sources of metal that could later serve as nucleation sites for the subsequent Co-alloy deposition. Copper-BTA complex, copper oxide (CuO_x) and other metal oxides, such as tantalum oxide (TaO_y), are removed from the substrate surface during this step. The amount of copper oxide to be removed depends on the contaminant level and depth of metal oxides on the surface. Metal complex and metal oxide can be removed by an O₂/Ar sputtering process, or a wet chemical removal process in an 1-step or a 2-step wet chemical process sequence. The preferred embodiment uses a wet process to remove the complexed metal and metal oxides. The wet chemical removal process can use an organic acid, such as DeerClean offered by Kanto Chemical Co., Inc. of Japan or a semi-aqueous solvent, such as ESC 5800 offered by DuPont of Wilmington, Del., an organic base such as tetramethylammonium hydroxide (TMAH), complexing amines such as ethylene diamine, diethylene triamine, or proprietary chemistry such as ELD clean andCap Clean 61, provided by Enthone, Inc. of West Haven, Conn. Removing Cu-BTA from the dielectric surface ensures that copper from the Cu-BTA complex will not be oxidized to copper oxide and subsequently reduced to copper during other surface preparation steps, reducing selectivity and providing nucleation points on the dielectric surface on which to grow the Co alloy, causing shorts and increasing the leakage current. Therefore, Cu-BTA removal process can also reduce yield loss due to metal shorting or current leakage.
• Cu-BTA complexes and other metal oxide contaminants are two key metal contaminants to be removed during this step, which can be done in either a controlled or uncontrolled ambient (or environment). For example, Cu-BTA can be removed by a wet clean process that involves a cleaning solution including tetramethylammonium hydroxide (TMAH), complexing amines such as ethylene diamine, diethylene triamine, or proprietary cleaning chemistries such as ELD clean andCap Clean 61, provided by Enthone, Inc. of West Haven, Conn. Metal oxides, specifically copper oxide, can be removed using a weak organic acid such as citric acid, or other organic or inorganic acids can be used. Additionally, very dilute (i.e. <0.1%) peroxide-containing acids, such as sulfuric-peroxide mixtures, can also be used. The wet clean process can also remove other metal or metal oxide residues.
• The presence of BTA on the copper lines of different pattern or feature types, such as small dense, small isolated or wide copper lines, is a result of passivation of the lines, the amount of which is related, in part, to the degree of the galvanic effect occurring on these features. This can result in the formation of pattern-dependent passivation layers. This dependence can further influence the Co-alloy deposition characteristics, resulting in pattern-dependent deposition characteristics, sometimes referred to as incubation or initiation effects. Removing BTA from the Cu lines can help eliminate this pattern-dependent deposition effect of cobalt-alloy (to be deposited at a subsequent step) and allow uniform cobalt-alloy deposition in the dense and isolated features.
• The organic contaminants can be removed by an oxidizing plasma such as an oxygen-containing plasma process instep403. The oxygen (O₂) plasma process is preferably conducted at a relatively low temperature of less than 120° C. High temperature O₂plasma process tends to oxidize copper into a thicker layer, making it harder to reduce later. Therefore, a low temperature O₂plasma process is preferred. In one embodiment, the O₂plasma process can be a downstream plasma process. Alternatively, organic residues (or contaminants) can also be removed by using an O₂/Ar sputtering process to physically remove the organic contaminants. O₂plasma process and O₂/Ar sputtering process are typically operated under less than 1 Torr.
• Once the substrate surface is free of contaminants, such as Cu-BTA, metal oxide, and other organic contaminants, the substrate should be exposed to as little oxygen as possible to protect the copper surface from oxidation. Copper oxidation is not a self-limiting process. The amount and duration of oxygen the copper surface is exposed to should be limited (or controlled) to minimize the copper oxide formation. Although copper oxide will be reduced at a later step, thicker layers of copper oxide may not be fully reduced. Therefore, it is important to limit the exposure of copper to oxygen to only that needed to remove the organic contaminants. To achieve controlled and limited exposure to oxygen, the substrate should be transferred or processes in controlled environments, such as an environment under vacuum or an environment filled with inert gas (es).
• To ensure that the copper surface is free of copper oxide, the substrate surface is reconditioned in a reducing environment to convert any residual copper oxide into copper atstep405. The previous pre-clean steps will have removed any metals from the dielectric layer, and thus metal reduction is performed only on the copper lines. The copper surface reduction can be achieved by a hydrogen-containing plasma process to convert copper oxide to copper (or substantially copper). Exemplary reactive gases that can be used to generate the hydrogen-containing plasma include hydrogen (H₂), ammonia (NH₃), and carbon monoxide (CO). For example, the substrate surface is reduced by a hydrogen-containing plasma, which is generated by hydrogen (H₂) gas, ammonia (NH₃) gas, or a combination of both gases, and the substrate is at an elevated temperature of between 20° C. and 300° C. In one embodiment, the hydrogen plasma process is a downstream plasma process. Once the substrate goes through a hydrogen reduction process, the substrate is ready for the cobalt-alloy deposition. The copper surface needs to be carefully protected to ensure no copper oxide formation. As described above, electroless deposition of cobalt-alloy can be inhibited by the presence of copper oxide. Therefore, it is important to control the processing and transport environments to minimize the exposure of the copper surface to oxygen.
• Atnext process step407, the cobalt-alloy, such as CoWP, CoWB or CoWBP, is electrolessly deposited on top of the copper surface. The electroless deposition of the cobalt-alloy is a wet process, and deposits on catalytic surfaces, such as copper surface, only. The cobalt-alloy only deposits selectively on the copper surface.
• After the electroless deposition of the cobalt-alloy, the process flow can enter anoptional process step409 of a post-deposition clean. Post-deposition clean can be accomplished by using a brush scrub clean with a chemical solution, such as a solution containing CP72B supplied by Air Products and Chemical, Inc. of Allentown, Pa. Other substrate surface cleaning processes can also be used, such as Lam's C3™ or P3™ cleaning technology. Other post clean chemicals can include a hydroxylamine-based chemistry to remove any metal-based contaminants that might remain on the dielectric surface after electroless plating.
• As described above, the process and wafer transfer environment control is very important for preparing the copper surface for cobalt-alloy deposition, especially after the hydrogen plasma reduction of the copper surface.FIG. 4B shows a schematic diagram of an exemplaryintegrated system450 that allows minimal exposure of substrate surface to oxygen at critical steps after surface treatment. In addition, since it is an integrated system, the substrate is transferred from one process station immediately to the next process station, which limits the duration that the prepared copper surface is exposed to oxygen. Theintegrated system450 can be used to process substrate(s) through the entire process sequence offlow400 ofFIG. 4A.
• As described above, the surface treatments, electroless deposition of cobalt-alloy and the optional post-cobalt-alloy deposition process involve a mixture of dry and wet processes. The wet processes are typically operated near atmosphere, while the dry O₂plasma, hydrogen plasma, and O₂/Ar sputtering are all operated at less than 1 Torr. Therefore, the integrated system needs to be able to handle a mixture of dry and wet processes. Theintegrated system450 has 3 substrate transfer modules (or chambers)460,470, and480.Transfer chambers460,470 and480 are equipped with robots to movesubstrate455 from one process area to another process area. The process area could be a substrate cassette, a reactor, or a loadlock.Substrate transfer module460 is operated under lab ambient, which refers to the laboratory (or factory) environment that is under room temperature, atmospheric pressure and exposed to air, usually HEPA- or ULPA-filtered to control particle defects.Module460 interfaces with substrate loaders (or substrate cassettes)461 to bring thesubstrate455 into the integrated system or to return the substrate to the cassette(s)461 to continue processing outside thesystem450.
• As described above inprocess flow400, thesubstrate455 is brought to theintegrated system450 to be deposited with a cobalt-alloy, such as CoWB, CoWP, or CoWBP, after the substrate has been planarized by metal CMP to remove excess metal from the substrate surface and leaves the metal only in the metal trenches, as shown inFIG. 2C. As described instep401 ofprocess flow400, the substrate, surface needs to be removed of surface contaminants such as Cu-BTA complex and other metal oxide residues. Cu-BTA and metal oxides can be removed by a wet clean process involving clean solution, such as a solution containing TMAH or complexing amines such as, but not limited to, ethylene diamine or diethylamine triamine. Following BTA-metal complex removal, metal oxides remaining on the copper and dielectric surfaces can be removed using a wet clean process involving a clean solution such as a solution containing citric acid, or other organic acid that can remove copper oxide more or less selectively to copper. Metal oxides, specifically copper oxide, can be removed using a weak organic acid such as citric acid, or other organic or inorganic acids can be used. Additionally, very dilute (i.e. <0.1%) peroxide-containing acids, such as sulfuric-peroxide mixtures, can also be used. The wet clean process can also remove other metal or metal oxide residues.
• A wetclean reactor463 can be integrated with the lab-ambient transfer module460, which is operated at lab ambient condition. The wetclean reactor463 can be used to perform the 1-step or 2-step clean described above atstep401 ofFIG. 4A. Alternatively, an additional wetclean reactor463′ can be integrated with the lab-ambient transfer module460 to allow the first step of the 2-step cleaning process to be performed inreactor463 and the second step be performed inreactor463′. For example, a cleaning solution containing chemical such as TMAH for cleaning Cu-BTA is inreactor463 and a cleaning solution containing a weak organic acid such as citric acid for cleaning metal oxide is inreactor463′.
• A lab ambient condition is under atmosphere and open to air. Although the wetclean reactor463 can be integrated with the lab-ambient transfer module460 in theprocess flow400, this process step can also be performed right after metal CMP and before the substrate is brought to the integrated system for cobalt-alloy deposition. Alternatively, the wet cleaning process can be performed in a controlled ambient process environment, where the controlled ambient is maintained during and after the wet cleaning step.
• Organic residues (or contaminants) not removed by the previous wet cleans can be removed by a dry oxidizing plasma process, such as oxygen-containing plasma, O₂/Ar sputter, or Ar sputter following the removal of Cu-BTA and metal oxides. As described above, most plasma or sputtering processes are operated below 1 Torr; therefore, it is desirable to couple such systems (or apparatus, or chambers, or modules) to a transfer module that is operated under vacuum at pressure, such as under 1 Torr. If the transfer module integrated with the plasma process is under vacuum, substrate transfer is more time efficient and the process module is maintained under vacuum, since it does not require extended time to pump down the transfer module. In addition, since the transfer module is under vacuum, the substrate after cleaning by the plasma process is exposed to only very low levels of oxygen. Assuming the O₂plasma process is selected to clean the organic residues, the O₂plasma process reactor471 is coupled to avacuum transfer module470.
• Since lab-ambient transfer module460 is operated at atmosphere andvacuum transfer module470 is operated under vacuum (<1 Torr), aloadlock465 is placed between these two transfer modules to allowsubstrate455 to be transferred between the two modules,460 and470, operated under different pressures.Loadlock465 is configured to be operated under vacuum at pressure less than 1 Torr, or at lab ambient, or to be filled with an inert gas selected form a group of inert gases.
• Aftersubstrate455 finishes the oxidizing plasma processing using O₂, for example,substrate455 is moved into the hydrogen-containing reducing plasma reduction chamber (or module)473. Hydrogen-containing plasma reduction is typically processed at a low pressure, which is less than 1 Torr; therefore, it is coupled to thevacuum transfer module470. Once thesubstrate455 is reduced with hydrogen-containing plasma, the copper surface is clean and free of copper oxide. In a preferred embodiment, aftersubstrate455 finishes the O₂plasma processing, a H₂or H₂/NH₃plasma reduction step can be performed in-situ, without removing the wafer from the chamber. In either case, the substrate is ready for cobalt-alloy deposition after completion of the reduction process.
• As described above, it is important to control the processing and transport environments to minimize the exposure of the copper surface to oxygen after the substrate is reconditioned by the hydrogen-containing reducing plasma. Thesubstrate455 should be process under a controlled environment, where the environment is either under vacuum or filled with one or more inert gas to limit the exposure ofsubstrate455 to oxygen.Dotted line490 outlines the boundary of a part of theintegrated system450 ofFIG. 4B that show the processing systems and transfer modules whose environment is controlled. Transferring and processing under controlledenvironment490 limits the exposure of the substrate to oxygen.
• Cobalt-alloy electroless deposition is a wet process that involves cobalt species in a solution that is reduced by a reducing agent, which can be phosphorous-based (e.g. hypophosphite), boron-based (e.g. dimethylamine borane), or a combination of both phosphorous-based and boron-based. The solution that uses phosphorous-based reducing agent deposits CoWP. The solution that uses boron-based reducing agent deposit CoWB. The solution that uses both phosphorous-based and boron-based reducing agents deposits CoWBP. In one embodiment, the cobalt-alloy electroless deposition solution is alkaline-based. Alternatively, cobalt-alloy electroless deposition solution can also be acidic. Since wet process is typically conducted under atmospheric pressure, thetransfer module480 that is coupled to the electroless deposition reactor should be operated near atmospheric pressure. To ensure the environment is controlled to be free of oxygen, inert gas (es) can be used to fill the controlled-ambient transfer module480. Additionally, all fluids used in the process are de-gassed, i.e. dissolved oxygen is removed by commercially available degassing systems. Exemplary inert gas includes nitrogen (N₂), helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe).
• In one embodiment, the wet cobalt-alloy electroless deposition reactor (or apparatus, or system, or module) is coupled with a rinse and dry system (or apparatus, or module) to allow the substrate to be transferred into theelectroless deposition system481 under dry condition and to come out of thesystem481 in dry condition (dry-in/dry-out). The dry-in/dry-out requirement allows theelectroless deposition system481 to be integrated with the controlled-ambient transfer module480, and avoids the need of a wet robotic transfer step to a separate rinse-dry module. The environment of theelectroless deposition system481 also needs to be controlled to provide low (or limited) levels of oxygen and moisture (water vapor). Inert gas can also be used to fill the system to ensure low levels of oxygen are in the processing environment.
• Alternatively, cobalt-alloy electroless deposition can also be conducted in a dry-in/dry-out manner similar to electroless copper disclosed recently. A dry-in/dry-out electroless copper process has been developed for copper electroless deposition. The process uses a proximity process head to limit the electroless process liquid in contacting with the substrate surface on a limited region. The substrate surface not under the proximity process head is dry. Details of such process and system can be found in U.S. application Ser. No. 10/607,611, titled “Apparatus And Method For Depositing And Planarizing Thin Films On Semiconductor Wafers,” filed on Jun. 27, 2003, and U.S. application Ser. No. 10/879,263, titled “Method and Apparatus For Plating Semiconductor Wafers,” filed on Jun. 28, 2004, both of which are incorporated herein in their entireties. The electroless plating of cobalt-alloy can use similar proximity processing head to enable a dry-in/dry-out process.
• After cobalt-alloy deposition insystem481, thesubstrate455 can be sent through an optional post-deposition cleaning reactor. This can be performed using mechanical assists, such as a brush scrub using chemistry such as CP72B or hydroxylamine-based cleaning chemistries or by using other methods, such as immersion cleaning, spin-rinse cleaning, or C3™ proximity technology. A rinse and dry system must also be integrated with the brush scrub system to allowsubstrate455 to be dry-in/dry-out of thewet cleaning system483. Inert gas (es) is used to fillsystem483 to ensure limited (or low) oxygen is present in the system. Thesystem483 is dotted to illustrate that this system is optional, since the post-deposition cleaning is optional, as described above inFIG. 4A. Since the post-deposition clean step is the last process that is to be operated by theintegrated system450, thesubstrate455 needs to be brought back intocassette461 after processing. Therefore, thecleaning system483 can alternatively be coupled to the lab-ambient transfer module460, as shown inFIG. 4B. If thecleaning system483 is coupled to the lab-ambient transfer module460, thecleaning system483 is not operated under controlled environment and inert gas (es) does not need to fill the system.
• As described above, the Cu-BTA and metal oxide removal process step(s) can also be performed right after metal CMP and before the substrate is brought to the integrated system for cobalt-alloy deposition.
Case II: Metal CMP Stops on Barrier Layer
• FIGS. 5A-5C show the cross sections of an interconnect structure at various stages of processing. The copper layer on the substrate ofFIG. 5A has been planarized by CMP. Thebarrier layer130 has not been removed, and remains on the substrate surface.FIG. 6A shows an embodiment of a process flow of surface preparation for electrolessly depositing a cobalt-alloy over copper in the dual-damascene metal trench. The substrate(s) used in theprocess flow600 ofFIG. 6A have just finished copper CMP processing(s) to remove copper. Barrier layer still remains on the substrate surface, as shown inFIG. 5A. The difference between Case II and Case I is that in Case II the surface ofdielectric106 is not exposed to Cu-BTA complex or other copper compound residues. The dielectric surface has higher quality (or less metal contaminants) in Case II than in Case I. Therefore, process step(s) aiming at removing copper oxide on the dielectric layer, which is formed after O₂plasma used to remove organic contaminants, can be eliminated.
• The process starts atstep601 of removing metallic contaminants, such as Cu-BTA or metal oxides, from the substrate surface. As described above, Cu-BTA complexes and metallic oxides are two key surface metallic contaminants to be removed. The processes used to remove metallic contaminants, such as Cu-BTA and metal oxides, from the substrate surface have been described above. For example, Cu-BTA and metal oxides, including copper oxides, can be removed by a wet clean process that involves a cleaning solution that includes, for example, tetramethylammonium hydroxide (TMAH) or complexing amines such as ethylenediamine or diethylenetriamine Removing Cu-BTA eliminates pattern-dependent deposition effect of cobalt-alloy (to be deposited at a later step) and hence allows uniform cobalt-alloy deposition in the dense and isolated features.
• Metal oxides, specifically copper oxide, can be removed using a weak organic acid such as citric acid, or other organic or inorganic acids can be used. Additionally, very dilute (i.e. <0.1%) peroxide-containing acids, such as sulfuric-peroxide mixtures, can also be used. The wet clean process can also remove other metal or metal oxide residues.
• The organic contaminants, including remaining BTA on the Cu and bather surfaces, are removed atstep602. Organic contaminants can be removed by a process such as a dry oxygen (O₂) plasma process or other oxidizing plasma processes, such as plasma process with H₂O, ozone, or hydrogen peroxide vapor. As described above, the oxygen-containing plasma process is preferably conducted at a relatively low temperature, below 50° C. and preferably below 120° C. The oxygen-containing plasma process can be a downstream plasma process. Alternatively, organic residues (or contaminants) can also be removed by using an O₂/Ar sputtering process to physically remove the organic contaminants. As described above, O₂plasma process and O₂/Ar sputtering process are typically operated under less than 1 Torr.
• Once the substrate surface is free of contaminants, such as Cu-BTA, metal oxides and organic contaminants, the substrate should be exposed to as little oxygen as possible to protect the copper surface from further oxidation. After surface contaminants are removed, atstep603, barrier layer, such as Ta, TaN, Ru, or a combination of the materials, is removed from substrate surface, as shown inFIG. 5B. Barrier layer can be removed by processes, such as CF₄plasma, O₂/Ar sputtering, CMP, or by a wet chemical etch. Both CF₄plasma etch and O₂/Ar sputtering processes are operated at less than 1 Torr.
• Copper oxide existing at thecopper surface140 ofFIG. 5A and produced during the plasma oxidation step might be completely removed during the barriermetal removal step603. Therefore, the process of using H-containing plasma to reduce copper surface becomes optional. However, to ensure that the copper surface is free of copper oxide, the substrate surface can (optionally) be reduced to convert any residual copper oxide into copper atstep605. The copper surface reduction can be achieved by a hydrogen-containing plasma process to convert copper oxide to copper. Process gas (es) and process condition used by the hydrogen-containing plasma process have been described above in Case I. Once the substrate went through a hydrogen reduction process, the substrate is ready for the cobalt-alloy deposition. The copper surface needs to be carefully protected from oxygen to ensure no copper oxide formation. As described above, electroless deposition of cobalt-alloy can be inhibited by the presence of copper oxide. Therefore, it's important to control the processing and transport environments to minimize or to eliminate the exposure of the copper surface to oxygen.
• Atnext process step607, the cobalt-alloy, such as CoWP, CoWB or CoWBP, is electrolessly deposited on the top of the copper surface. Cobalt-alloy is shown aslayer135 inFIG. 5C. The electroless deposition of the cobalt-alloy is a selective deposition and is a wet process. The cobalt-alloy only deposits on the copper surface.
• As described above for Case I, after the electroless deposition of the cobalt-alloy, the process flow can enter anoptional process step609 of a post-deposition clean. Post-deposition clean can be performed by using a brush scrub clean with a chemical solution, such as a solution containing CP72B supplied by Air Products and Chemical, Inc. of Allentown, Pa., or by hydroxylamine-base chemicals, in order to removal any metal contaminants on the dielectric surface introduced by the electroless deposition process. Other substrate surface cleaning processes can also be used.
• As described above, the environment control is very important for preparing the copper surface for cobalt-alloy deposition, especially after the H-containing plasma reduction of the copper surface.FIG. 6B shows a schematic diagram of an exemplaryintegrated system650 that allows minimal exposure of substrate surface to oxygen at critical steps after surface treatment. Theintegrated system650 can be used to process substrate(s) through the entire process sequence offlow600 ofFIG. 6A.
• Similar to theintegrated system450, theintegrated system650 has 3substrate transfer modules660,670, and680.Transfer modules660,670 and680 are equipped with robots to movesubstrate655 from one process area to another process area.Substrate transfer module660 is operated under lab ambient.Module660 interfaces with substrate loaders (or substrate cassettes)661 to bring thesubstrate655 into the integrated system or to return the substrate to the cassette(s)661 to continue processing outside thesystem650.
• As described above inprocess flow600, thesubstrate655 is brought to theintegrated system650 to be deposited with a cobalt-alloy, such as CoWB, CoWP, or CoWBP, after the substrate has been planarized by copper CMP to remove excess copper from the substrate surface and leaves barrier layer on the dielectric surface and copper in the metal trenches, as shown inFIG. 5A. As described instep601 ofprocess flow600, the substrate surface needs to be removed of surface contaminants such as Cu-BTA, metal oxides and organic residues. Cu-BTA and metal oxides can be removed by a wet clean process involving clean solution, such as a solution containing TMAH. A wetclean reactor663 can be integrated with the lab-ambient transfer module660. Although the wetclean reactor663 can be integrated with the lab-ambient transfer module660 in theprocess flow600, this process step can also be performed right after metal CMP and before the substrate is brought to the integrated system for cobalt-alloy deposition. Alternatively, the wet cleaning process can be performed in a controlled ambient process environment, where the controlled ambient is maintained during and after the wet cleaning step.
• Organic residues (or contaminants) not removed by the wetclean process601 performed inreactor683 can be removed by a dry plasma process, such as O₂plasma or O₂/Ar sputter, atstep602. As described above, most plasma or sputtering processes are operated below 1 Torr; therefore, it's desirable to couple such systems to a transfer module that is operated under vacuum at pressure, such as under 1 Torr. Assuming O₂plasma process is selected to clean the organic residue, the O₂plasma process reactor671 is coupled to avacuum transfer module670.
• The O₂plasma process can be a downstream plasma process. Although the O₂plasma reactor671 can be integrated with thevacuum transfer module670 in theprocess flow600, this process step can also be performed right after metal CMP and before the substrate is brought to the integrated system for cobalt-alloy deposition.
• Since lab-ambient transfer module660 is operated under atmosphere andvacuum transfer module670 is operated under vacuum (<1 Torr), aloadlock665 is placed between these two transfer modules to allowsubstrate655 to be transferred between the two modules,660 and670.
• Aftersubstrate655 finishes the O₂plasma processing,substrate655 is moved into a processing system for barrier layer etch, as shown instep603. The barrier layer etch chamber (or module)673, if a dry barrier plasma etch process is selected, can be coupled to thevacuum transfer module670. The dry barrier plasma process can be a CF₄plasma process or an O₂/Ar sputtering process.
• The process following barrier layer etch is an optional H-containing plasma reduction to ensure no copper oxide remains on the copper surface. The H₂plasma reduction can be performed in a plasma chamber (or module)674, which is coupled to thevacuum transfer module670. Alternatively, hydrogen plasma reduction can also be performed sequentially in the O₂plasma reactor671 used to remove organic residues after purging the chamber of residual oxygen species.
• As described above, cobalt-alloy electroless deposition is a wet chemical process. Since a wet process is typically conducted at atmospheric pressure, thetransfer module680 that is coupled to the electroless deposition reactor should be operated near atmospheric pressure. To ensure the environment is controlled to be free of oxygen, inert gas (es) can be used to fill the controlled-ambient transfer module680. Additionally, all fluids used in the process are de-gassed, i.e. dissolved oxygen is removed by commercially available degassing systems.
• The wet cobalt-alloy electroless deposition reactor needs to be coupled with a rinse and dry system to allow the substrate to be transferred to theelectroless deposition system681 under dry conditions and to come out of thesystem681 in dry condition (dry-in/dry-out). As described above, the dry-in/dry-out requirement allows theelectroless deposition system681 to be integrated with the controlled-ambient transfer module680. Inert gas (es) is used to fillsystem681 to ensure low (or limited, or controlled) oxygen levels are maintained in the system.
• After cobalt-alloy deposition insystem681, thesubstrate655 can be sent through apost-deposition cleaning reactor683. A rinse and dry system also needs to be integrated with the brush scrub system to allowsubstrate655 to be dry-in/dry-out of thewet cleaning system683. Inert gas (es) is used to fillsystem683 to ensure no oxygen is present. Thesystem683 is dotted to illustrate that this system is optional, since the post-deposition cleaning is optional, as described above inFIG. 6A. Since the post-deposition clean step is the last process that is to be operated by theintegrated system650, thesubstrate655 needs to be brought back into cassette661 after processing. Thecleaning system683 can alternatively be coupled to the lab-ambient transfer module660.
Case III: Metal CMP Stops on a Thin Copper Layer
• FIGS. 7A-7C show cross sections of an interconnect structure at various stages of interconnect processing. The substrate inFIG. 7A has just finished copper planarization, but has not fully cleared the copper from the substrate. Athin copper layer132 remains on the substrate surface.FIG. 8A shows an embodiment of a process flow of surface preparation for electrolessly depositing a cobalt-alloy over copper in the dual-damascene metal trench. The substrate(s) used in theprocess flow800 ofFIG. 8A have just finished copper CMP processing(s) to remove most of the copper above the barrier layer over dielectric layer. A thin layer of copper in the range between about 100 angstrom to about 1000 angstrom is left on the barrier surface, as shown inFIG. 7A. The difference between Case III and both Case I and Case II is that in Case III a thin layer of copper cover the entire substrate surface; therefore there is no concern of galvanic corrosion of copper due to exposed dissimilar materials in the copper CMP solution. Since the thin copper layer and other surface contaminants present will be removed in an oxygen-free environment, there is no concern of copper oxidation. Therefore, no H₂plasma reduction is needed. Both Case II and Case III do not have barrier CMP; therefore, metal CMP processing cost is reduced. The copper surface prepared by this process allows excellent selectivity of cobalt-alloy on the copper versus on dielectric layer.
• The process starts atstep801 of removing contaminants, including organic residues and inorganic metal oxides, from the substrate surface. The organic contaminants can be removed by an oxidizing plasma such as a dry oxygen (O₂) plasma process, H₂O plasma process, H₂O₂plasma process, or a plasma with ozone vapor. As described above, the O₂plasma process is preferably conducted at a relatively low temperature less than 120° C. The O₂plasma process can be a downstream plasma process. Alternatively, organic residues (or contaminants) can also be removed by using an O₂/Ar sputtering process to physically remove the organic contaminants. As described above, O₂plasma process and O₂/Ar sputtering process are typically operated under less than 1 Torr.
• Once the substrate surface is free of contaminants, the substrate should be exposed to as little oxygen as possible to protect the copper surface from oxidation. After surface contaminants are removed, atstep803, the thin copper layer over the barrier layer and dielectric layer is removed. The thin copper layer can be removed by O₂/Ar sputtering, by O₂/hexafluoroacetylacetone (HFAC) plasma etch, by a wet chemical etch using chemicals, such as sulfuric acid and hydrogen peroxide, or by using complexing chemistries. Both O₂/Ar sputtering and O₂/HFAC plasma processes are operated under low pressure, such as below 1 Torr.
• Afterwards, the barrier layer, such as Ta, TaN, or a combination of both films, is removed from substrate surface atstep805. The cross-section of the interconnect structure after the removal of the thin copper and barrier is shown inFIG. 7B. Barrier layer can be removed by CF₄plasma, O₂/Ar sputtering, CMP, or by a wet chemical etch. Both CF₄plasma etch and O₂/Ar sputtering processes are operated at below 1 Torr.
• Since the copper surface to selectively deposit the cobalt-alloy is created by etching the thin copper layer and the barrier layer above dielectric in controlled-ambient environments, the step of using H-containing plasma to reduce the copper surface is mostly not needed. However, to ensure that the copper surface is free of copper oxide, the substrate surface can optionally be reduced to convert any residual copper oxide into copper atstep807. The copper surface reduction process has been described above. Once the substrate went through a hydrogen-containing reduction process, the substrate is ready for the cobalt-alloy deposition. The copper surface needs to be carefully protected to prevent copper oxide formation. Atnext process step809, the cobalt-alloy, such as CoWP, CoWB or CoWBP, is electrolessly deposited on the top of the copper surface. Cobalt-alloy is shown aslayer135 inFIG. 7C. The electroless deposition of the cobalt-alloy is a selective deposition and is a wet process. The cobalt-alloy only deposits on the copper surface.
• As described above for Case I and Case II, after the electroless deposition of the cobalt-alloy, the process flow can enter anoptional process step811 of a post-deposition clean. Post-deposition clean has been described above in Case I and Case II.
• As described above, the environment control is very important for preparing the copper surface for cobalt-alloy deposition, especially after the H-containing plasma reduction of the copper surface.FIG. 8B shows a schematic diagram of an exemplaryintegrated system850 that allows minimal exposure of substrate surface to oxygen at critical steps after surface treatment. Theintegrated system850 can be used to process substrate(s) through the entire process sequence offlow800 ofFIG. 8A.
• Theintegrated system850 has 3substrate transfer modules860,870, and880.Transfer modules860,870 and880 are equipped with robots to movesubstrate855 from one process area to another process area.Substrate transfer module860 is operated under lab ambient.Module860 interfaces with substrate loaders (or substrate cassettes)861 to bring thesubstrate855 into the integrated system or to return the substrate to the cassette(s)861 to continue processing outside thesystem850.
• As described above inprocess flow800, thesubstrate855 is brought to theintegrated system850 to be deposited with a cobalt-alloy, such as CoWB, CoWP, or CoWBP, after the substrate has been planarized by copper CMP to remove excess copper from the substrate surface and leaves a thin copper layer on the barrier layer that is over the dielectric surface, as shown inFIG. 7A. As described instep801 ofprocess flow800, the substrate surface needs to be removed of surface contaminants such organic residues and non-copper metal oxides. Due to the elimination of the need to perform a wet Cu-BTA clean, in contrast to Case I and Case II, the lab-ambient transfer module860 can possibly be eliminated to allowcassette holders861 to be directly coupled toloadlock865.
• Surface contaminants including organic residues and metal oxides can be removed by an oxidizing plasma process such as O₂plasma or O₂/Ar sputter. As described above, most plasma or sputtering processes are operated below 1 Torr; therefore, it's desirable to couple such systems to a transfer module that is operated under vacuum at pressure, such as under 1 Torr. Assuming O₂plasma process is selected to clean the organic residue, the O₂plasma process reactor871 is coupled to avacuum transfer module870.
• The O₂plasma process can be a downstream plasma process. Although the O₂plasma reactor871 can be integrated with thevacuum transfer module870 in theprocess flow800, this process step can also be performed right after metal CMP and before the substrate is brought to the integrated system for cobalt-alloy deposition.
• Since lab-ambient transfer module860 is operated under atmosphere andvacuum transfer module870 is operated under vacuum (<1 Torr), aloadlock865 is placed between these two transfer modules to allowsubstrate855 to be transferred between the two modules,860 and870.
• Aftersubstrate855 finishes the O₂plasma processing,substrate855 is moved into a processing system for copper etch, as shown instep803. The copper etch chamber (or module)873, if a dry copper plasma etch process is selected, is coupled to thevacuum transfer module870. If a wet process is selected, the wet copper etch reactor can be integrated with a rinse/dry system to become a wetcopper etch system873′ that can be coupled to the controlled-ambient transfer module880. To enable the wetcopper etch system873′ to be integrated with the controlled-ambient transfer module880, dry-in and dry-out of substrate to thesystem873′ are required. In one embodiment, a rinse and dry system can be integrated in the wetcopper etch system873′ to meet the dry-in/dry-out requirement. The environment ofsystem873′ also needs to be controlled to be free of oxygen. Inert gas can also be used to fill the system to ensure no oxygen is in the processing environment.
• Barrier layer etch follows copper etch, as shown instep805. The barrierlayer etch chamber874, if a dry barrier plasma etch process is selected, can be coupled to thevacuum transfer module870. If a wet barrier etch process is selected, the wet barrier etch reactor can be integrated with a rinse/dry system to become a wetbarrier etch system874′ that can be coupled to the controlled-ambient transfer module880. To enable the wetbarrier etch system874′ to be integrated with the controlled-ambient transfer module880, dry-in and dry-out of substrate to thesystem874′ are required. The environment ofsystem874′ also needs to be controlled to provide low (or limited, or controlled) levels of oxygen. Inert gas can also be used to fill the system to ensure low oxygen levels are achieved in the processing environment.
• The process following barrier layer etch is an optional H-containing plasma reduction as discussed above. The H₂plasma reduction can be performed in aplasma chamber877, which is coupled to thevacuum transfer module870.
• As described above, cobalt-alloy electroless deposition is a wet process. Since wet process is typically conducted under atmospheric pressure, thetransfer module880 that is coupled to the electroless deposition reactor should be operated near atmospheric pressure. To ensure the environment is controlled to provide low levels of oxygen, inert gas (es) can be used to fill the controlled-ambient transfer module880. Additionally, all fluids used in the process are de-gassed, i.e. dissolved oxygen is removed by commercially available degassing systems. Exemplary inert gas includes nitrogen (N₂), helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe).
• The wet cobalt-alloy electroless deposition reactor needs to be coupled with a rinse and dry system to allow the substrate to go into theelectroless deposition system881 under dry condition and to come out of thesystem881 in dry condition (dry-in/dry-out). The dry-in/dry-out requirement allows theelectroless deposition system881 to be integrated with the controlled-ambient transfer module880. Inert gas (es) is used to fillsystem881 to ensure a low oxygen level is present in the system.
• After cobalt-alloy deposition insystem881, thesubstrate855 can be sent through a post-deposition cleaning reactor. A rinse and dry system also need to be integrated with the brush scrub system to allowsubstrate855 to be dry-in/dry-out of thewet cleaning system883. Inert gas (es) is used to fillsystem883 to ensure no oxygen is present. Thesystem883 is dotted to illustrate that this system is optional, since the post-deposition cleaning is optional, as described above inFIG. 8A. Since the post-deposition clean step is the last process that is to be operated by theintegrated system850, thesubstrate855 needs to be brought back intocassette861 after processing. Thecleaning system883 can alternatively be coupled to the lab-ambient transfer module860.
2. Engineering Barrier Surface for Electroless Copper Deposition
• The system concept describe above can be used to prepare barrier surface for copper plating. Barrier layer, such as Ta, TaN or Ru, if exposed to air for extended period of time, can form Ta_xO_y(Tantalum oxide), TaO_xN_y(Tantalum oxynitride), or RuO₂(Ruthenium oxide). Electroless deposition of a metal layer on a substrate is highly dependent upon the surface characteristics and composition of the substrate. Electroless plating of copper on a Ta, TaN, or Ru surface is of interest for both seed layer formation prior to electroplating, and selective deposition of Cu lines within lithographically defined pattern(s). One concern is the inhibition of the electroless deposition process by atomically thin native metal oxide layer formed in the presence of oxygen (O₂).
• In addition, copper film does not adhere to the barrier oxide layer, such as tantalum oxide, tantalum oxynitride, or ruthenium oxide, as well as it adheres to the pure barrier metal or barrier-layer-rich film, such as Ta, Ru, or Ta-rich TaN film. Ta and/or TaN barrier layers are only used as examples. The description and concept apply to other types of barrier metals, such as Ta or TaN capped with a thin layer of Ru. As described above, poor adhesion can negatively affect the EM performance. In addition, the formation tantalum oxide or tantalum oxynitride on the barrier layer surface can increase the resistivity of the barrier layer. Due to these issues, it is desirable to use the integrated system to prepare the barrier/copper interface to ensure good adhesion between the barrier layer and copper and to ensure low resistivity of the barrier layer.
Case I: Metal Line Formation
• FIG. 9A shows an exemplary cross-section of a metal line structure after being patterned by a dielectric etch and being removed of photoresist. The metal line structure(s) is on asubstrate900 and has asilicon layer110, which was previously fabricated to form agate structure105 with agate oxide121,spacers107 and acontact125 therein. Thecontact125 is typically fabricated by etching a contact hole into theoxide103 and then filling the contact hole with a conductive material, such as tungsten. Alternative materials may include copper, aluminum or other conductive materials. Thebarrier layer102 is also configured to function as a selective trench etch stop. Thebarrier layer102 can be made of materials such as silicon nitride (SiN) or silicon carbide (SiC).
• A metalline dielectric layer106 is deposited over thebarrier layer102. The dielectric materials that can be used to deposit106 have been described above. After the deposition ofdielectric layer106, the substrate is patterned and etched to createmetal trenches106.FIG. 9B shows that after the formation ofmetal trenches116, a metallic barrier layer, a barrier layer containing a metallic element,130 is deposited to linemetal trench116.FIG. 9C shows that after thebarrier layer130 is deposited, acopper layer132 is deposited over thebarrier layer130. Thebarrier layer130 can be made of tantalum nitride (TaN), tantalum (Ta), Ru, or a combination of these films. Acopper film132 is then deposited to fill themetal trench116. In one embodiment, thecopper film132 includes a thincopper seed layer131 underneath.
• After using plasma surface pre-treatments to prepare a catalytic surface for the deposition of a conformal and thin electrolessCu seed layer131, andcopper film132 fillingtrenches116,substrate900 is chemically and mechanically polished (CMP) or wet etched to remove the copper material (or copper overburden) and bather layer (or barrier overburden) over the surface ofdielectric106, as shown inFIG. 9D. In one embodiment, the thickness of the thin copper seed layer is between about 5 angstroms to about 300 angstroms. The next step is to cap thecopper surface140 with a copper/SiC interfaceadhesion promoter layer135, such as a cobalt-alloy, as shown inFIG. 9E. Examples of the cobalt-alloy include: CoWP, CoWB, or CoWBP, which can be selectively deposited over copper by an electroless process. The thickness of the adhesion promoter layer can be as thin as a monolayer, which is only a few angstroms, such as 5 angstroms, to a thicker layer, such as 200 angstroms.
• FIG. 10A shows an embodiment of aprocess flow1000 of preparing the barrier (or liner) layer surface for electroless copper deposition after the trenches have been formed. It should be noted, however, that the barrier (or liner) layer may be prepared separately in a non-integrated deposition system, such as an ALD or PVD deposition reactor. In this case, the surface preparation for depositing a thin copper seed layer would not include the metal plug preclean and barrier deposition process steps. Atstep1001, thetop surface124aof the contact plug is cleaned to remove native metal oxide. Metal oxide can be removed by an Ar sputtering process, a plasma process using a fluorine-containing gas, such as NF₃, CF₄, or a combination of both, a wet chemical etch process, or a reduction process, for example using a hydrogen-containing plasma. Atstep1003, a barrier layer is deposited. Due to the shrinking metal line and via critical dimension, the barrier layer may be deposited by atomic layer deposition (ALD), depending on the technology node. The thickness of thebather layer130 is between about 20 angstroms to about 200 angstroms. As described above, preventing the barrier layer from exposure to oxygen is critical in ensuring that electroless copper is being deposited on the barrier layer with good adhesion between copper and the barrier layer. Once the barrier layer is deposited, the substrate should be transferred or processed in a controlled-ambient environment to limit exposure to oxygen. The barrier layer is hydrogen-plasma treated to produce a metal-rich surface on the Ta, TaN, or Ru layer atoptional step1005 to provide a catalytic surface for the subsequent copper seed deposition step. Whether this step is needed or not depends on how metal-rich the surface is.
• Afterwards, conformal copper seed is deposited on the barrier surface atstep1007, followed by a thick copper gap fill (or bulk fill) process,1008. In one embodiment, the conformal copper seed layer can be deposited by an electroless process. The thick copper bulk fill process can be an electroless deposition (ELD) process or an electrochemical plating (ECP) process. Electroless copper deposition and ECP are well-known wet process. For a wet process to be integrated in a system with controlled processing and transporting environment, which has been described above, the reactor needs to be integrated with a rinse/dryer to enable dry-in/dry-out process capability. In addition, the system needs to be filled with inert gas to ensure minimal exposure of the substrate to oxygen. Recently, a dry-in/dry-out electroless copper process has been developed. Further, all fluids used in the process are de-gassed, i.e. dissolved oxygen is removed by commercially available degassing systems.
• The electroless deposition process can be carried out in a number of ways, such as puddle-plating, where fluid is dispensed onto a substrate and allowed to react in a static mode, after which the reactants are removed and discarded, or reclaimed. In another embodiment, the process uses a proximity process head to limit the electroless process liquid is only in contact with the substrate surface on a limited region. The substrate surface not under the proximity process head is dry. Details of such process and system can be found in U.S. application Ser. No. 10/607,611, titled “Apparatus And Method For Depositing And Planarizing Thin Films Of Semiconductor Wafers,” filed on Jun. 27, 2003, and U.S. application Ser. No. 10/879,263, titled “Method and Apparatus For Plating Semiconductor Wafers,” filed on Jun. 28, 2004, both of which are incorporated herein in their entireties. The electroless plating of cobalt-alloy described earlier can also use similar proximity processing head to enable a dry-in/dry-out process.
• After copper deposition atsteps1007 and1008, the substrate can undergo an optional substrate cleaning atstep1009. Post-copper-deposition clean can be accomplished by using a brush scrub clean with a chemical solution, such as a solution containing CP72B supplied by Air Products and Chemical, Inc. of Allentown, Pa. Other substrate surface cleaning processes can also be used, such as Lam's C3™ or P3™ cleaning technology.
• FIG. 10B shows an embodiment of a schematic diagram of anintegrated system1050 that allows minimal exposure of substrate surface to oxygen at critical steps after barrier surface preparation. In addition, since it is an integrated system, the substrate is transferred from one process station immediately to the next process station, limiting the duration that clean copper surface is exposed to low levels of oxygen. Theintegrated system1050 can be used to process substrate(s) through the entire process sequence offlow1000 ofFIG. 10A.
• As described above, the surface preparation for electroless deposition of copper and the optional post-cobalt-alloy deposition processes involves a mixture of dry and wet processes. The wet processes are typically operated near atmosphere, while the dry plasma processes are operated at less than 1 Torr. Therefore, the integrated system needs to be able to handle a mixture of dry and wet processes. Theintegrated system1050 has 3substrate transfer modules1060,1070, and1080.Transfer modules1060,1070 and1080 are equipped with robots to movesubstrate1055 from one process area to another process area. The process area could be a substrate cassette, a reactor, or a loadlock.Substrate transfer module1060 is operated under lab ambient.Module1060 interfaces with substrate loaders (or substrate cassettes)1061 to bring thesubstrate1555 into the integrated system or to return the substrate to one of thecassettes1061.
• As described above inprocess flow1000, thesubstrate1055 is brought to theintegrated system1050 to deposit barrier layer and copper layer. As described instep1001 ofprocess flow1000,top tungsten surface124aofcontact125 is etched to remove native tungsten oxide. Once the tungsten oxide is removed, the exposedtungsten surface124aofFIG. 9A needs to be protected from exposure to oxygen. If the removal process is an Ar sputtering process, thereactor1071 is coupled to thevacuum transfer module1070. If a wet chemical etching process is selected, the reactor should be coupled to the controlled-ambient transfer module1080, not the lab-ambient transfer module1060, to limit exposure of the tungsten surface to oxygen.
• Afterwards, the substrate is deposited with a metallic barrier layer, such as Ta, TaN, Ru, or a combination of these films, as described instep1003 ofFIG. 10A. Thebarrier layer130 ofFIG. 9B can be deposited by an ALD process or a PVD process. In one embodiment, the ALD process is operated at less than 1 Torr. TheALD reactor1073 is coupled to thevacuum transfer module1070. In another embodiment, the deposition process is a high pressure process using supercritical CO₂and organometallic precursors to form the metal barrier. In yet another embodiment, the deposition process is a physical vapor deposition (PVD) process operating at pressures less than 1 Torr. Details of an exemplary reactor for a high pressure process using supercritical CO₂is described in commonly assigned application Ser. No. 10/357,664, titled “Method and Apparatus for Semiconductor Wafer Cleaning Using High-Frequency Acoustic Energy with Supercritical Fluid”, filed on Feb. 3, 2003, which in incorporated herein for reference.
• The substrate can undergo an optional reduction process, for example using a hydrogen-containing plasma, as described instep1005 ofFIG. 10A. Thehydrogen reduction reactor1074 can be coupled to thevacuum transfer module1070. At this stage, the substrate is ready for electroless copper deposition. The electroless copper plating can be performed in an electrolesscopper plating reactor1081 to deposit a conformal seed layer. Following the seed layer deposition, copper bulk fill can be performed in the same electrolesscopper deposition reactor1081 used to deposit the conformal seed layer, but with a different chemistry to achieve bulk fill. Alternatively, copper bulk fill can be performed in aseparate ECP reactor1081′.
• Before the substrate leaves theintegrated system1050, the substrate can optionally undergo a surface cleaning process, which can clean residues from the previous copper deposition process. For example, the substrate cleaning process can be brush clean process.Substrate cleaning reactor1083 can be integrated with the controlled-ambient transfer module1080. Alternatively,substrate cleaning reactor1083 can also be integrated with the lab-ambient transfer module1060.
• Alternatively, thebarrier layer130 ofFIG. 9B can be deposited in a process chamber before thesubstrate900 is brought into a system for surface treatment and depositing copper.FIG. 10C shows an embodiment of aprocess flow1090 of preparing the barrier (or liner) layer surface for electroless copper deposition. The barrier surface is hydrogen-plasma treated to produce a metal-rich surface on the Ta, TaN, or Ru layer atoptional step1095 to provide a catalytic surface for the subsequent copper seed deposition step. Whether this step is needed or not depends on how metal-rich the surface is.
• Afterwards, conformal copper seed is deposited on the barrier surface atstep1097, followed by a thick copper gap fill (or bulk fill) process,1098. In one embodiment, the conformal copper seed layer can be deposited by an electroless process. The thick copper bulk fill process can be an electroless deposition (ELD) process or an electrochemical plating (ECP) process. After copper deposition atsteps1097 and1098, the substrate can undergo an optional substrate cleaning atstep1099. Post-copper-deposition clean can be accomplished by using a brush scrub clean with a chemical solution, such as a solution containing CP72B supplied by Air Products and Chemical, Inc. of Allentown, Pa. Other substrate surface cleaning processes can also be used, such as Lam's C3™ or P3™ cleaning technology.
• FIG. 10D shows an embodiment of a schematic diagram of anintegrated system1092 that allows minimal exposure of substrate surface to oxygen at critical steps after barrier surface preparation. In addition, since it is an integrated system, the substrate is transferred from one process station immediately to the next process station, limiting the duration that clean copper surface is exposed to low levels of oxygen. Theintegrated system1092 can be used to process substrate(s) through the entire process sequence offlow1090 ofFIG. 10C.
• As described above, the surface preparation for electroless deposition of copper and the optional post-cobalt-alloy deposition processes involves a mixture of dry and wet processes. The wet processes are typically operated near atmosphere, while the dry plasma processes are operated at less than 1 Torr. Therefore, the integrated system needs to be able to handle a mixture of dry and wet processes. Theintegrated system1092 has 3substrate transfer modules1060,1070, and1080.Transfer modules1060,1070 and1080 are equipped with robots to movesubstrate1055 from one process area to another process area. The process area could be a substrate cassette, a reactor, or a loadlock.Substrate transfer module1060 is operated under lab ambient.Module1060 interfaces with substrate loaders (or substrate cassettes)1061 to bring thesubstrate1555 into the integrated system or to return the substrate to one of thecassettes1061.
• As described above inprocess flow1090, thesubstrate1055 is brought to theintegrated system1092 after the barrier layer is deposited to prepare the barrier surface for electroless copper deposition. The substrate first undergoes a reduction process, for example using a hydrogen-containing plasma, as described instep1095 ofFIG. 10C. Thehydrogen reduction reactor1074 can be coupled to thevacuum transfer module1070. At this stage, the substrate is ready for electroless copper deposition. The electroless copper plating can be performed in an electrolesscopper plating reactor1081 to deposit a conformal seed layer. Following the seed layer deposition, copper bulk fill can be performed in the same electrolesscopper deposition reactor1081 used to deposit the conformal seed layer, but with a different chemistry to achieve bulk fill. Alternatively, copper bulk fill can be performed in aseparate ECP reactor1081′.
• Before the substrate leaves theintegrated system1092, the substrate can optionally undergo a surface cleaning process, which can clean residues from the previous copper deposition process. For example, the substrate cleaning process can be brush clean process.Substrate cleaning reactor1083 can be integrated with the controlled-ambient transfer module1080. Alternatively,substrate cleaning reactor1083 can also be integrated with the lab-ambient transfer module1060.
• FIG. 11A shows an embodiment of a process flow of preparing the bather (or liner) layer surface for electroless copper deposition and preparing the post-CMP copper surface for electroless cobalt-alloy deposition. Atstep1101, thetop surface124aof the contact plug is cleaned to remove native tungsten oxide. Metal oxide can be removed by an Ar sputtering process, a plasma reduction process, a reactive ion etch process, or a wet chemical etch process. Atstep1103, a barrier layer is deposited. The barrier layer is hydrogen-plasma treated to produce a metal-rich surface on the Ta, TaN or Ru layer atoptional step1005 to provide a catalytic surface for the subsequent copper seed deposition step. Whether this step is needed or not depends on how metal-rich the surface is.
• It should be noted, however, that the barrier (or liner) layer may be prepared separately in a non-integrated deposition system, such as an ALD or PVD deposition reactor. In this case, the surface preparation for depositing a thin copper seed layer would not include the metal plug preclean and barrier deposition process steps as described inFIG. 10A,step1001 and1003, andFIG. 11A, steps1101,1103. In these cases, the process described would commence atstep1005 or1105.
• Afterwards, conformal copper seed is deposited on the barrier surface atstep1107, followed by a thick copper gap fill (or bulk fill) process,1108. In one embodiment, the conformal copper seed layer can be deposited by an electroless process. The thick copper bulk fill process can be an electroless deposition process (ELD) or an electrochemical plating (ECP) process. Electroless copper deposition and ECP are well-known wet processes. For a wet process to be integrated in a system with controlled processing and transporting environment, which has been described above, the reactor needs to be integrated with a rinse/dryer to enable dry-in/dry-out process capability. In addition, the system needs to be filled with inert gas to ensure minimal exposure of the substrate to oxygen. Recently, a dry-in/dry-out electroless copper process has been developed. Further, all fluids used in the process are de-gassed, i.e. dissolved oxygen is removed by commercially available degassing systems.
• After the substrate is deposited with conformal copper seed atstep1107, and thick Cu gap fill (bulk fill) by either an electroless or electro-plating process atstep1108, thecopper layer132 is removed from the substrate surface abovebarrier layer130 over dielectric106 atstep1109, as shown inFIG. 9D. Barrier layer is removed afterwards. Both removal processes are performed inprocess step1109 ofFIG. 11A. Removing copper from the surface above barrier layer can be accomplished by CMP, which is a wet process. Barrier layer can be removed by using a reactive ion etch, such as CF₄-plasma, O2/Ar sputtering, CMP, or a wet chemical etch. These barrier etch processes have been described previously.
• After barrier layer removal, a cleaning process to remove Cu-BTA complexes and metal oxides (step1110) and an organic contaminants removal process (step1111) are performed to remove contaminants from the substrate surface. Details of substrate surface cleaning using these two steps after metal CMP have been described above.
• After substrate surface is removed of surface contaminants, the substrate is treated with a reducing plasma (hydrogen-containing) to reduce all residual metal oxide into metal atstep1112. After hydrogen reduction, the copper surface is very clean and catalytic, and is ready for electroless deposition of the cobalt-alloy. Atstep1113, the substrate undergoes electroless deposition of cobalt-alloy with a rinse and dry of substrate. Thelast process step1115 is an optional substrate-cleaning step to clean any residual contaminants from the previous electroless cobalt-alloy deposition.
• FIG. 11B shows an embodiment of a schematic diagram of anintegrated system1150 that allows minimal exposure of substrate surface to oxygen at critical steps after barrier and copper surface preparation. In addition, since it is an integrated system, the substrate is transferred from one process station immediately to the next process station, which limits the duration that clean copper surface is exposed to low levels of oxygen. Theintegrated system1150 can be used to process substrate(s) through the entire process sequence offlow1100 ofFIG. 11A.
• Theintegrated system1150 has 3substrate transfer modules1160,1170, and1180.Transfer modules1160,1170 and1180 are equipped with robots to movesubstrate1155 from one process area to another process area. The process area could be a substrate cassette, a reactor, or a loadlock.Substrate transfer module1160 is operated under lab ambient.Module1160 interfaces with substrate loaders (or substrate cassettes)1161 to bring thesubstrate1155 into the integrated system or to return the substrate to one of thecassettes1161.
• As described above inprocess flow1100 ofFIG. 11A, thesubstrate1155 is brought to theintegrated system1150 to deposit barrier layer, to prepare barrier surface for copper layer deposition, and to prepare post-CMP copper surface for electroless cobalt-alloy deposition. As described instep1101 ofprocess flow1100, topmetal plug surface124aofcontact125 is etched to remove native metal oxide. Alternatively, the metal plug surface oxide can be removed using a reducing plasma, such as a hydrogen-containing plasma. Once the metal plug surface oxide is removed, the exposedmetal surface124aofFIG. 9A needs to be protected from exposure to oxygen. If the removal process is an Ar sputtering process, theAr sputtering reactor1171 is coupled to thevacuum transfer module1170. If a wet chemical etching process is selected, the reactor should be coupled to the controlled-ambient transfer module1180, not the lab-ambient transfer module1160, to limit the exposure of the clean metal plug surface to oxygen.
• Afterwards, the substrate is deposited with a metallic barrier layer, such as Ta, Ru, TaN, or a combination of these films, as described in astep1103 ofFIG. 11A. Thebarrier layer130 ofFIG. 9B can be deposited by an ALD process or a PVD process. In one embodiment, the ALD process is operated at less than 1 Torr. TheALD reactor1173 is coupled to thevacuum transfer module1170. In another embodiment, the deposition process is a high pressure process using supercritical CO₂and organometallic precursors to form the metal barrier. In yet another embodiment, the deposition process is a physical vapor deposition (PVD) process operating at pressures less than 1 Torr. The substrate can undergo an optional reduction process, for example using a hydrogen-containing plasma, as described instep1105 ofFIG. 11A. Thehydrogen reduction reactor1174 can be coupled to thevacuum transfer module1170. At this stage, the substrate is ready for electroless copper deposition. The electroless copper plating can be performed in an electrolesscopper plating reactor1181 to deposit a conformal seed layer. Following the seed layer deposition, copper bulk fill can be performed in the same electrolesscopper deposition reactor1181 used to deposit the conformal seed layer, but with a different chemistry to achieve bulk fill. Alternatively, copper bulk fill can be performed in aseparate ECP reactor1181′.
• Afterwards, the substrate is removed of copper overburden and barrier overburden, as described instep1109 ofFIG. 11A. The removal of copper overburden and barrier over burden can be accomplished in oneCMP system1183, or in two CMP systems. In the embodiment shown inFIG. 11A, only oneCMP system1183 is used. After CMP removal of copper and barrier overburdens, the substrate surface needs to be cleaned to remove surface contaminants Wetclean system1185 is used to remove copper BTA complexes and metal oxides. O₂plasma system1177 is used to remove organic contaminants. In one embodiment, O₂plasma process to remove organic contaminants can be performed in thehydrogen reduction chamber1174.
• After the removal of contaminants, the substrate undergoes a reduction process, as described instep1112 ofFIG. 11A. The hydrogen reduction process can occur in thesame reduction reactor1174 used to reduce the bather surface to be Ta-rich. Following hydrogen reduction treatment, the copper surface is ready for electroless cobalt-alloy deposition, which can be performed inreactor1187.
• Before the substrate leaves theintegrated system1150, the substrate can optionally undergo a surface cleaning process, which can clean residues from the previous copper plating process. The substrate cleaning process can be brush clean process, whosereactor1163 can be integrated with the lab-ambient transfer module1160.
• The wet processing systems described inFIG. 15B, which are coupled to the controlled-ambient transfer module1180, all need to meet the requirement of dry-in/dry-out to allow system integration.
Case II: Dual Damascene Interconnect Sequence
• FIG. 12A shows an exemplary cross-section of an interconnect structure after being patterned by a dual damascene process. The interconnect structure(s) is on asubstrate1200 and has anoxide layer100, which was previously fabricated to form ametallization line101 therein. The metallization line is typically fabricated by etching a trench into theoxide100 and then filling the trench with conductive material, such as copper.
• In the trench, there is abarrier layer120, used to prevent thecopper material122 from diffusing into theoxide100. Thebarrier layer120 can be made of tantalum nitride (TaN), tantalum (Ta), ruthenium (Ru), or a combination of these films. Other barrier layer materials can also be used. Abarrier layer102 is deposited over thecopper material122 to provide an etch stop during the via etch process, and to act as a diffusion barrier between dielectric layers for the copper. Thebarrier layer102 can be made of materials such as silicon nitride (SiN) or silicon carbide (SiC) or other materials suitable for integration into the dual Damascene process flow.
• A viadielectric layer104 is deposited over thebarrier layer102. The viadielectric layer104 can be made of inorganic dielectric materials such as silicon dioxide, or preferably low-K dielectric materials. Exemplary dielectrics can include an un-doped TEOS silicon dioxide, fluorinated silica glass (FSG), organo-silicate glass (OSG), porous OSG, commercially available dielectric materials include Black Diamond (I) and Black Diamond (II), Coral, Aurora. After the viadielectric layer104 is deposited, a patterning and etching process is used to form the via holes114. Thecopper surface122ais protected by the dielectric barrier layer, such as SiC or Si₃N₄.FIG. 12A shows the dual Damascene structure after the formation of viaholes114, andtrenches116. Thedielectric barrier layer102 under viaholes114 has been removed.
• FIG. 12B shows that after the formation of viaholes114 andtrenches116, afirst barrier layer130_I, asecond barrier layer130_II, and acopper layer132 are deposited to line the via holes114′ and thetrenches116. Both barrier layers130_I,130_IIcan be made of tantalum nitride (TaN), tantalum (Ta), or ruthenium (Ru). Other barrier layer materials can also be used. In one embodiment, thefirst barrier layer130_Iis a thin TaN layer deposited by ALD and thesecond barrier layer130_IIis a very thin Ta layer deposited by flash PVD or Ru layer deposited by ALD or PVD. In one embodiment, the thickness of thefirst barrier layer130_Iis between about 10 angstroms to about 150 angstroms and the thickness of thesecond barrier layer130_IIis between about 10 angstroms to about 50 angstroms. The thin ALD TaN layer provides conformal coverage of a barrier layer over the via114′ andtrench116. The thin PVD Ta or Ru layer provides good adhesion to thecopper film132 to be deposited over the barrier layers130_Iand130_II. Typically, barrier layer deposited by PVD process does not have good step coverage (or the film is not conformal). Therefore, an ALD barrier is needed to ensure good barrier coverage inside via and trench. In another embodiment, thefirst barrier layer130_Iand thesecond barrier layer130_IIis combined into one single layer, which can be deposited by ALD or by PVD. The material of this single layer barrier can be tantalum, tantalum nitride, ruthenium, or a combination of these films.
• After the deposition of the first and second barrier layers130_I,130_II, the substrate undergoes previously described requite surface treatment steps to ensure the barrier surface is Ta-rich. Acopper film132 is then deposited, either using aPVD seed131 orelectroless seed131 followed by a thick gap-fill copper layer to fill the via holes114 and thetrenches116.
• Aftercopper film132 fills the via holes114 andtrenches116,substrate1200 is planarized to remove the copper material (or copper overburden) and barrier layer (or barrier overburden) over the surface ofdielectric106, as shown inFIG. 12C. The substrate then undergoes previously described requite surface treatment steps to ensure the substrate surface is clean and the copper surface is removed of copper oxide. The next step is to cap thecopper surface140 with a copper/SiC interfaceadhesion promoter layer135, such as a cobalt-alloy, as shown inFIG. 16D. Examples of the cobalt-alloy include: CoWP, CoWB, or CoWBP, which can be selectively deposited over copper by an electroless process. The thickness of the adhesion promoter layer can be as thin as a monolayer, which is only a few angstroms, to a thicker layer, such as 200 angstroms.
• FIG. 13A shows an embodiment of a process flow of preparing the bather (or liner) layer surface for electroless copper deposition and preparing the post-CMP copper surface for electroless cobalt-alloy deposition. Atstep1301, thetop surface122aof themetal lines101 is cleaned to remove native copper oxide. Copper oxide can be removed by an Ar sputtering process or a wet chemical etch process. Atstep1302, a first barrier layer (130_IofFIG. 12B) is deposited in an ALD system. Atstep1303, a second barrier layer (130II ofFIG. 12B) is deposited in a PVD system. As described above, preventing the barrier layer from exposure to oxygen is critical in ensuring that electroless copper is being deposited on the barrier layer with good adhesion between copper and the barrier layer. Once the barrier layer is deposited, the substrate should be transferred or processed in a controlled-ambient environment to limit exposure to oxygen. The barrier layer is treated by a reducing plasma (i.e. hydrogen-containing) atstep1305 to produce a metal-rich layer that will provide a catalytic surface for the subsequent copper seed deposition step. The reducing plasma treatment is optional, depending on the composition of the surface.
• Afterwards, a conformal copper seed is deposited on the barrier surface atstep1307, followed by a thick copper bulk fill (or gap fill) process,1308. The conformal copper seed layer can be deposited by an electroless process. The thick copper bulk fill (also gap fill) layer can be deposited by an ECP process. Alternatively, the thick bulk fill (also gap fill) layer can be deposited by an electroless process in the same electroless system for conformal copper seed, but with a different chemistry.
• After the substrate is deposited with conformal copper seed atstep1307, and thick Cu bulk fill by either an electroless or electro-plating process atstep1308, thecopper layer132 is removed from the substrate surface abovebarrier layer130 over dielectric106 atstep1309, as shown inFIG. 11C. Barrier layer is removed afterwards. Both removal processes are performed inprocess step1309 ofFIG. 13A. Removing copper from the surface above barrier layer can be accomplished by CMP, which is a wet process. Barrier layer can be removed by using CF₄plasma, O2/Ar sputtering, CMP, or a wet chemical etch. These barrier etch processes have been described previously.
• After barrier layer removal, a cleaning process to remove Cu-BTA complexes and metal oxides (step1310) and an organic contaminants removal process (step1311) are performed to remove contaminants from the substrate surface. Details of substrate surface cleaning using these two steps after metal CMP have been described above.
• After substrate surface is removed of surface contaminants, the substrate is treated with a reducing plasma, for example a hydrogen-containing plasma, to reduce all residual metal oxide into metal atstep1312. After hydrogen reduction, the copper surface is very clean and catalytic, and is ready for electroless deposition of the cobalt-alloy. Atstep1313, the substrate undergoes electroless deposition of cobalt-alloy with a rinse and dry of substrate. Thelast process step1315 is an optional substrate-cleaning step to clean any residual contaminants from the previous electroless cobalt-alloy deposition.
• FIG. 13B shows an embodiment of a schematic diagram of anintegrated system1350 that allows minimal exposure of substrate surface to oxygen at critical steps after barrier and copper surface preparation. In addition, since it is an integrated system, the substrate is transferred from one process station immediately to the next process station, which limits the duration that clean copper surface is exposed to low levels of oxygen. Theintegrated system1350 can be used to process substrate(s) through the entire process sequence offlow1300 ofFIG. 13A.
• Theintegrated system1350 has 3substrate transfer modules1360,1370, and1380.Transfer modules1360,1370 and1380 are equipped with robots to movesubstrate1355 from one process area to another process area. The process area could be a substrate cassette, a reactor, or a loadlock.Substrate transfer module1360 is operated under lab ambient.Module1360 interfaces with substrate loaders (or substrate cassettes)1361 to bring thesubstrate1355 into the integrated system or to return the substrate to one of thecassettes1361.
• As described above inprocess flow1300 ofFIG. 11A, thesubstrate1355 is brought to theintegrated system1350 to deposit barrier layer, to prepare barrier surface for copper layer deposition, and to prepare post-CMP copper surface for electroless cobalt-alloy deposition. As described instep1301 ofprocess flow1300,top copper surface122aofmetal lines101 is etched to remove native copper oxide. Once the copper oxide is removed, the exposedtungsten surface122aofFIG. 12A needs to be protected from exposure to oxygen. If the removal process is an Ar sputtering process, theAr sputtering reactor1371 is coupled to thevacuum transfer module1370. If a wet chemical etching process is selected, the reactor should be coupled to the controlled-ambient transfer module1380, not the lab-ambient transfer module1360, to limit the exposure of the clean tungsten surface to oxygen.
• Afterwards, the substrate is deposited with first and second barrier layers. Thefirst barrier layer130_IofFIG. 12B is deposited by an ALD process, which is a dry process and is operated at less than 1 Torr. TheALD reactor1372 is coupled to thevacuum transfer module1370. Thesecond barrier layer130_IIofFIG. 12B is deposited by a PVD or ALD process, which is a dry process and is operated at less than 1 Torr. ThePVD reactor1373 is coupled to thevacuum transfer module1370. The substrate can undergo an optional hydrogen reduction process to ensure the barrier layer surface is metal-rich for electroless copper deposition. Thehydrogen reduction reactor1374 can be coupled to thevacuum transfer module1370. At this stage, the substrate is ready for electroless copper deposition. The electroless copper plating can be performed in an electrolesscopper plating reactor1381 to deposit a conformal copper seed layer, as described instep1307 ofFIG. 13A. As described above, the deposition of the gap fill copper layer atstep1308 ofFIG. 13A can be deposited in the sameelectroless plating reactor1381 with different chemistry, or in aseparate ECP reactor1381′.
• Afterwards, the substrate is removed of copper overburden and barrier overburden, as described instep1309 ofFIG. 13A. The removal of copper overburden and barrier over burden can be accomplished in oneCMP system1383, or in two CMP systems. In the embodiment shown inFIG. 13A, only oneCMP system1383 is used. After CMP removal of copper and barrier overburden, the substrate surface needs to be cleaned to remove surface contaminants. Wetclean system1385 is used to remove copper BTA complexes and metal oxides. O₂plasma system1377 is used to remove organic contaminants. In one embodiment, O₂plasma process to remove organic contaminants can be performed in thehydrogen reduction chamber1374.
• After the removal of contaminants, the substrate undergoes a reduction process, as described instep1312 ofFIG. 13A. The hydrogen reduction process is used to reduce copper oxide to copper and can occur in thesame reduction reactor1374 used to reduce the barrier surface to be Ta-rich. Following hydrogen reduction treatment, the copper surface is ready for electroless cobalt-alloy deposition, which can be performed inreactor1387.
• Before the substrate leaves theintegrated system1350, the substrate can optionally undergoes a surface cleaning process, which can clean residues from the previous copper plating process. The substrate cleaning process can be brush clean process, whosereactor1163 can be integrated with the lab-ambient transfer module1360.
• The wet processing systems described inFIG. 13B, which are coupled to the controlled-ambient transfer module1380, all need to meet the requirement of dry-in/dry-out to allow system integration.
• The apparatus and methods (or processes) described above apply to preparing metal surface for subsequent metal deposition to improve metal-to-metal adhesion and EM performance. The inventive concept can also apply to preparing silicon surface for subsequent selective metal layer deposition.
3. Engineering a Silicon Surface for Selective Electroless Metal Deposition to Form Metal Silicide
• The processes described so far are used to improve the EM performance, metal resistivity, and even yield for copper interconnects, such as contacts, vias and metal lines. Earlier in the fabrication sequence of ICs, another metal deposition is applied on silicon or polysilicon surface to form metal silicide in the source/drain/gate, resistor, contact-landing regions (such as resistor contact landing region) of structures, gate region, capacitor region or inductor region of the device to reduce contact resistance and provide good ohmic contact.FIG. 14A is a cross section of agate structure127 that includes athin gate oxide121, apolysilicon layer105 and anitride spacer107 on asilicon substrate110. Shallow trench isolation (STI)65 is used to separate active devices. On two sides of the gate structure aresource area61 anddrain area63. On thesource area61, there is an exposedsilicon surface62. On thedrain area63, there is an exposedsilicon surface64. On thepolysilicon layer105, there is an exposedpolysilicon109. Metal silicide is formed to reduce sheet resistance.
• To form metal silicide, ametal111, such as nickel (Ni), titanium (Ti), or cobalt (Co), is first deposited on the silicon surface, as shown inFIG. 14B. Currently,metal111 is deposited on the substrate surface by a PVD process, and is not selective to the silicon or dielectric regions. The metal is then annealed to form the metal-silicon alloy (silicide) in regions where the metal is in contact with the silicon or polysilicon substrate. No silicide is formed in the dielectric regions. Un-reacted metal is removed selectively to the silicide, including metal in the dielectric regions as well as remaining un-reacted metal above the silicided regions. Electroless metal deposition can be an alternative process to replace the current Co or Ni deposition process. The advantages are that the metal-silicide layer can be made thicker and provide improved etch stop characteristics as well as allow metal-metal contact formation. To enable electroless metal deposition, the silicon surface needs to be very clean and free of native silicon oxide. Aftermetal111 is selectively deposited onsilicon surfaces62,64, the substrate is thermally treated at high temperature, such as between about 800° C. to about 900° C., to formmetal silicide113, as shown inFIG. 14C. Themetal silicide113 formed can allow contact125 to electrically communicate with thedrain area61, as shown inFIG. 14D.
• As describe above, the surface preparation prior to electroless metal deposition needs to be conducted in a controlled-ambient environment to ensure the surface on which will be performed electroless deposition is not exposed to oxygen.FIG. 15A show an embodiment for aprocess flow1500 used to form metal silicide. Atstep1501, metal contaminants are removed from all dielectric surfaces; this can be performed using known methods and chemistries.Step1501 is an optional step, which is needed only when there is concern of surface metal contamination. Organic contaminants are next removed from substrate surface,step1502. As mentioned above, organic contaminants can be removed by either a variety of dry or wet processes. Afterwards, atstep1503 the silicon surface is reduced to convert native silicon oxide to silicon. Native silicon oxide is a self-limiting process; therefore, the oxide layer is quite thin and does not need an oxide removal step prior to the reduction process. As described above, the reduction process can be a hydrogen plasma process.
• After the surface reduction, the silicon surface is ready for electroless metal deposition. A metal, such as Ni, Ti, or Co, is selectively deposited over the exposed silicon (including polysilicon) surface atstep1505. The selective metal deposition can be accomplished by an electroless process. After electroless metal deposition, the substrate undergoes an optional substrate cleaning using known methods and chemistries atstep1507. The substrate then undergoes a high temperature process (or annealing) to form metal silicide atstep1509.
• FIG. 15B shows an embodiment of anintegrated system1550 that includes a lab-ambient transfer module1560, a vacuum transfer module1950, and a controlled-ambient transfer module1580. The lab-ambient transfer module1560 is coupled tocassettes1561 that hold substrate(s)1555. In one embodiment, the metal contaminants are removed by a wet clean process, such as one of the wet clean processes used to remove metal contaminants described above. The wet clean can be performed inchamber1565 coupled to the lab-ambient transfer module1560. Since this process step is optional,chamber1565 inFIG. 15B is dotted. Following removal of metal contaminants, organic contaminants are removed. In one embodiment, the organic contaminants are removed in an oxidizing plasma, such as O₂, H2O, or ozone plasma, inreactor1571, coupled to thevacuum transfer module1570, since the O₂plasma process is a low pressure dry process, operated at pressure less than 1 Torr.
• Afterwards, silicon surface reduction atstep1503 offlow1500 can be performed inreactor1573. The substrate is then transferred to the next system to be deposited with the metal used to form metal silicide (or silicide metal) in anelectroless process reactor1581. The substrate is transferred fromreactor1573 throughvacuum transfer module1570, loadlock1575, and controlled-ambient transfer module1580, and finally arrives inreactor1581 for processing. The electrolessmetal deposition reactor1581 is equipped with a rinse/dry system. The substrate can undergo an optional substrate cleaning after metal deposition in a wetclean chamber1583, as described inprocess step1507 ofFIG. 15A. After the electroless deposition, the substrate is sent to athermal reactor1576, such as a rapid thermal processing (RTP) reactor, to form metal silicide.
• The systems described above allow substrate processing that requires a mixture of low pressure dry process, high pressure process, and wet processes to be integrated together to limit oxygen exposure at critical processing steps.FIG. 16 shows a schematic diagram that shows how different processes are integrated. The lab-ambient transfer module can integrate with cassettes, wet process (es), and dry process that do not need to limit exposure to oxygen (or not-controlled process). The vacuum transfer module can integrate low-pressure dry processes. The vacuum transfer module is operated under vacuum, such as less than 1 Torr; therefore, the exposure to oxygen is limited and controlled. Loadlock I enables substrate transport between the lab-ambient transfer module and the vacuum transfer module. Controlled-ambient transfer module can integrate wet processes, near atmospheric pressure processes, and high-pressure processes. The term “high pressure” is used to differentiate from low-pressure process. The pressure of the high-pressure process refers to pressure greater than atmospheric pressure process, such as the supercritical CO₂process described previously. In one embodiment, there is a loadlock (not shown) between the high-pressure process chamber and the controlled-ambient transfer module to enable substrate being efficiently transferred between the transfer module and the process chamber. Loadlock II enables substrates to be transferred between the vacuum transfer module and the controlled-ambient transfer module. The controlled-ambient transfer module and the reactors coupled to the controlled-ambient transfer module are filled with inert gas to limit exposure to oxygen. Loadlock II can be pump down to receive substrate from the vacuum transfer module. Loadlock II can also be filled with inert gas to exchange substrate with the controlled-ambient transfer module.
• While this invention has been described in terms of several embodiments, it will be appreciated that those skilled in the art upon reading the preceding specifications and studying the drawings will realize various alterations, additions, permutations and equivalents thereof. Therefore, it is intended that the present invention includes all such alterations, additions, permutations, and equivalents as fall within the true spirit and scope of the invention. In the claims, elements and/or steps do not imply any particular order of operation, unless explicitly stated in the claims.

Claims (20)

1. An integrated system for processing a substrate in controlled environment to enable deposition of a thin copper seed layer on a surface of a metallic barrier layer of a copper interconnect, comprising:

a lab-ambient transfer chamber capable of transferring the substrate from a substrate cassette coupled to the lab-ambient transfer chamber into the integrated system;

a vacuum transfer chamber operated under vacuum at a pressure less than 1 Torr, wherein at least one vacuum process module is coupled to the vacuum transfer chamber;

a vacuum process module for cleaning an exposed surface of a metal oxide of a underlying metal in the integrated system, wherein the underlying metal is part of a underlying interconnect, the copper interconnect is electrically connected to the underlying interconnect, wherein the vacuum process module for cleaning is one of the at least one vacuum process module coupled to the vacuum transfer chamber, and is operated under vacuum at a pressure less than 1 Torr;

a vacuum process module for depositing the metallic barrier layer, wherein the vacuum process module for depositing the metallic barrier layer is one of the at least one vacuum process module coupled to the vacuum transfer chamber, and is operated under vacuum at a pressure less than 1 Torr;

a controlled-ambient transfer chamber filled with an inert gas selected from a group of inert gases, wherein at least one controlled-ambient process module is coupled to the controlled-ambient transfer chamber; and

an electroless copper deposition process module used to deposit the thin layer of copper seed layer on the surface of the metallic barrier layer, wherein the electroless copper deposition process module is one of the at least one controlled environment process modules coupled to the controlled-ambient transfer chamber.

2. The integrated system ofclaim 1, further comprising:

a hydrogen-containing reduction process module used to reduce metal oxide or metal nitride on the surface of the metallic barrier, wherein the hydrogen-containing reduction process module is coupled to the vacuum transfer chamber, the hydrogen-containing reduction process module is operated under vacuum at a pressure less than 1 Torr.

3. The integrated system ofclaim 1, wherein the electroless copper deposition process module is also used to deposit a gap-fill copper layer over the thin copper seed layer.

4. The integrated system ofclaim 1, wherein another electroless copper deposition process module is used to deposit a gap-fill copper layer over the thin copper seed layer.

5. The integrated system ofclaim 1, further comprising:

a substrate cleaning process module used to clean the substrate surface after depositing the gap-fill copper layer over the thin layer copper seed layer, the substrate cleaning process module is one of the at least one vacuum process module coupled to the controlled-ambient transfer module.

6. The integrated system ofclaim 1, further comprising:

a first loadlock coupled to the vacuum transfer chamber and the controlled-ambient transfer chamber, wherein the first loadlock assists the substrate to be transferred between the vacuum transfer chamber and the controlled-ambient transfer chamber, the first loadlock being configured to be operated under vacuum at pressure less than 1 Torr or to be filled with an inert gas selected from a group of inert gases; and

a second loadlock coupled to the vacuum transfer chamber and the lab-ambient transfer chamber, wherein the second loadlock assists the substrate to be transferred between the vacuum transfer chamber and the lab-ambient transfer chamber, the second loadlock being configured to be operated under vacuum at pressure less than 1 Torr or at lab ambient or to be filled with an inert gas selected from a group of inert gases.

7. The integrated system ofclaim 1, wherein the vacuum transfer chamber and the at least one vacuum process module coupled to the vacuum transfer chamber are operated at a pressure less than 1 Torr to control the exposure of the substrate to oxygen.

8. The integrated system ofclaim 1, wherein the controlled-ambient transfer chamber and each one the at least one process module coupled to the controlled-ambient transfer chamber are filled with one or more inert gases selected from the group of inert gases to control the exposure of the substrate to oxygen.

9. The integrated system ofclaim 1, wherein substrate is transferred and processed in the integrated system to limit a duration the substrate is exposed to oxygen.

10. The method ofclaim 9, wherein limiting the exposure of the substrate surface to oxygen enables the thin layer of copper seed layer being selectively deposited on the surface of the metallic barrier layer.

11. The integrated system ofclaim 1, wherein the at least one process module coupled to the controlled-ambient transfer module enables a dry-in/dry-out processing of the substrate, wherein the substrate goes in and comes out the at least one process module in a dry state.

12. The integrated system ofclaim 11, wherein the electroless copper deposition process module is coupled to a rinse and dry system to enable the dry-in/dry-out processing.

13. An integrated system for processing a substrate in controlled environment to enable selective deposition of a thin copper seed layer on a surface of a metallic barrier layer of a copper interconnect and preparing a planarized copper surface of the copper interconnect to selectively depositing a thin layer of a cobalt-alloy material in an integrated system to improve electromigration performance of the copper interconnect, comprising:

a lab-ambient transfer chamber capable of transferring the substrate from a substrate cassette coupled to the lab-ambient transfer chamber into the integrated system;

a vacuum transfer chamber operated under vacuum at a pressure less than 1 Torr, wherein at least one vacuum process module is coupled to the vacuum transfer chamber;

an Ar sputtering process module to clean an exposed surface of a metal oxide of a underlying metal in the integrated system, wherein the underlying metal is part of a underlying interconnect, the copper interconnect is electrically connected to the underlying interconnect, the Ar sputtering process module one of the at least one vacuum process module is coupled to the vacuum transfer chamber;

an atomic layer deposition (ALD) process module for depositing a thin first metallic barrier layer, wherein the ALD process module is one of the at least one vacuum process module coupled to the vacuum transfer chamber;

a PVD process chamber for depositing a thin second metallic barrier layer, wherein the PVD process module is one of the at least one vacuum process module coupled to the vacuum transfer chamber;

a hydrogen reduction process module for reducing a metal oxide or metal nitride to a metal, wherein the hydrogen reduction process module is one of the at least one vacuum process module coupled to the vacuum transfer chamber;

an oxygen plasma process module for removing organic contaminants from the substrate surface, wherein the oxygen plasma process module is one of the at least one vacuum process module coupled to the vacuum transfer chamber;

a controlled-ambient transfer chamber filled with an inert gas selected from a group of inert gases, wherein at least one controlled-ambient process module is coupled to the controlled-ambient transfer chamber;

an electroless copper deposition process module used to deposit the thin layer of copper seed layer and a gap-fill copper layer on the surface of the metallic barrier layer, the electroless copper deposition process module being one of the at least one controlled-ambient process module coupled to the controlled-ambient transfer chamber;

an electroless cobalt-alloy deposition process module used to deposit the thin layer of the cobalt-alloy material on the prepared planarized copper surface, the electroless copper alloy deposition process module being one of the at least one controlled-ambient process module coupled to the controlled-ambient transfer chamber;

a planarizing process module used to remove a copper overburden and a bather overburden of the copper interconnect, the planarizing process module is one of the at least one controlled-ambient process module coupled to the controlled-ambient transfer module; and

a wet clean process module used to remove metallic contamination on the substrate surface, the wet clean process module is one of the at least one controlled-ambient process module coupled to the controlled-ambient transfer module.

14. The integrated system ofclaim 13, further comprising:

a substrate cleaning process module used to clean the substrate surface after depositing and planarizing the gap-fill copper layer over the thin layer copper seed layer and after depositing the thin layer of the cobalt-alloy material, the substrate cleaning process module being one of the at least one controlled-ambient process module coupled to the controlled-ambient transfer module.

15. The integrated system ofclaim 13, further comprising:

a first loadlock coupled to the vacuum transfer chamber and the controlled-ambient transfer chamber, wherein the first loadlock assists the substrate to be transferred between the vacuum transfer chamber and the controlled-ambient transfer chamber, the first loadlock being configured to be operated under vacuum at pressure less than 1 Torr or to be filled with an inert gas selected from a group of inert gases to operated under the same pressure as the controlled-ambient transfer module; and

a second loadlock coupled to the vacuum transfer chamber and the lab-ambient transfer chamber, wherein the second loadlock assists the substrate to be transferred between the vacuum transfer chamber and the lab-ambient transfer chamber, the second loadlock being configured to be operated under vacuum at pressure less than 1 Torr or at lab ambient or to be filled with an inert gas selected from a group of inert gases to operated under the same pressure as the controlled-ambient transfer module.

16. The integrated system ofclaim 13, wherein the controlled-ambient transfer chamber and each one the at least one controlled-ambient process module coupled to the controlled-ambient transfer chamber are filled with one or more inert gas selected from the group of inert gases to limit the exposure of the substrate to oxygen.

17. The integrated system ofclaim 13, wherein substrate is transferred and processed in the integrated system to limit a duration the substrate is exposed to oxygen.

18. The integrated system ofclaim 13, wherein limiting the exposure of the substrate surface to oxygen enables the thin layer of copper seed layer being selectively deposited on the surface of the metallic barrier layer.

19. The integrated system ofclaim 13, wherein the at least one process module coupled to the controlled-ambient transfer module enables a dry-in/dry-out processing of the substrate, wherein the substrate goes in and comes out the at least one process module in a dry state.

20. An integrated system for processing a substrate in controlled environment to enable deposition of a thin copper seed layer on a surface of a metallic barrier layer of a copper interconnect, comprising:

a lab-ambient transfer chamber capable of transferring the substrate from a substrate cassette coupled to the lab-ambient transfer chamber into the integrated system;

a vacuum transfer chamber operated under vacuum at a pressure less than 1 Torr, wherein at least one vacuum process module is coupled to the vacuum transfer chamber;

a vacuum process module for reducing the metallic barrier layer, wherein the vacuum process module for reducing the metallic barrier layer one of the at least one vacuum process module is coupled to the vacuum transfer chamber, and is operated under vacuum at a pressure less than 1 Torr;

a controlled-ambient transfer chamber filled with an inert gas selected from a group of inert gases, wherein at least one controlled-ambient process module is coupled to the controlled-ambient transfer chamber; and

an electroless copper deposition process module used to deposit the thin layer of copper seed layer on the surface of the metallic barrier layer, wherein the electroless copper deposition process module is one of the at least one controlled environment process modules coupled to the controlled-ambient transfer chamber.

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