US20020168863A1 - Selective treatment of the surface of a microelectronic workpiece - Google Patents

Abstract

In a process for treating a workpiece such as a semiconductor wafer, a processing fluid is selectively applied or excluded from an outer peripheral margin of at least one of the front or back sides of the workpiece. Exclusion and/or application of the processing fluid occurs by applying one or more processing fluids to the workpiece while the workpiece and a reactor holding the workpiece are spinning. The flow rate of the processing fluids, fluid pressure, and/or spin rate are used to control the extent to which the processing fluid is selectively applied or excluded from the outer peripheral margin.

Description

• This application is a division of U.S. patent application Ser. No. 09/437,926, filed Nov. 10, 1999, and now, pending, which claims the benefit of: International application No. PCT/US99/05674, filed Mar. 15, 1999, and the benefit of U.S. Provisional Patent Application Ser. No. 60/117,474, filed Jan. 27, 1999. The disclosures of those applications, as well as U.S. patent application Ser. No. 09/437,711, filed on Nov. 28, 1999, and now pending, are incorporated herein by reference. This application is also a continuation of U.S. patent application Ser. No. 09/881,246, filed on Jun. 12, 2001, and now pending, which is a division of U.S. patent application Ser. No. 09/041,649, filed on Mar. 13, 1998, now U.S. Pat. No. 6,318,385.[0001]
BACKGROUND OF THE INVENTION
• This invention pertains to treating a silicon wafer to remove a thin film, such as a copper film, from regions on the silicon wafer.[0002]
• The fabrication of a microelectronic circuit and/or component from a substrate typically involves a substantial number of processes. Many of these processes involve the deposition of a thin film on the surface of the workpiece followed by contact with a processing liquid, vapor, or gas. In a known process for treating a microelectronic workpiece, such as a silicon wafer, on which microelectronic devices have been fabricated and which has a front, device side, a back, non-device side, and an outer perimeter, thin-film layers are successively applied and etched to form, for example, a metallized interconnect structure. In a typical metallization process, a barrier layer is applied over a dielectric layer to the front side of the workpiece. Depending upon the particular process used to form the interconnect structures, the dielectric layer may include a pattern of recessed micro-structures that define the various interconnect paths. A thin metal film, such as a copper film, is applied exterior to the barrier layer. In most instances, the thin film serves as an initial seed layer for subsequent electroplating of a further metal layer, such as a further copper layer. Due to manufacturing constraints, the thin film is not applied over an outer, peripheral margin of the front side.[0003]
• Known techniques, such as physical vapor deposition (sputtering) or chemical vapor deposition, are typically used to apply the barrier layer and the thin film. In instances in which a further metal layer is to be electroplated exterior to the thin film, one or more electrical contacts are connected to an outer margin of the thin film to provide plating power.[0004]
• The surface area of the front side beyond the inner boundary of the outer margin of the thin film, is not available for fabricating the microelectronic devices since the present manufacturing processes limit the extent to which device structures can be formed at the outer margin. It would be highly desirable and would result in increased yield if more of the surface area beyond the present limits of the outer margin of the thin film were available for fabricating interconnect structures.[0005]
• In the known process discussed above, and in other processes, contamination by copper, other metals, or other contaminants can occur on the back side of the workpiece. Although copper and other metals tend to diffuse rapidly through silicon or silicon dioxide, the back side is generally not provided with barrier layers that are capable of preventing copper, other metals, or other contaminants from diffusing through the silicon wafer to the front side, at which such contamination can be very detrimental to device performance.[0006]
• Such contamination can result from overspraying or other processing artifacts or from cross-contamination via fabrication tools. Such contamination can occur on the outer perimeter of a silicon wafer as well as on its back side. If not removed, such contamination can lead to cross-contamination of other wafers, via fabrication tools. Such contamination can be very difficult to remove, particularly if the contaminant has formed a stable silicide. It would be highly desirable if such contamination could be easily removed in a controlled manner without detrimentally affecting the front side of the workpiece.[0007]
SUMMARY OF THE INVENTION
• In a first aspect of the invention, a processing fluid is selectively applied or excluded from an outer peripheral margin of at least one of the front or back sides of the workpiece. Exclusion and/or application of the processing fluid occurs by applying one or more processing fluids to the workpiece as the workpiece, and a reactor holding the workpiece, are spinning. The flow rate of the one or more processing fluids, fluid pressure, and/or spin rate are used to control the extent to which the processing fluid is selectively applied or excluded from the outer peripheral margin.[0008]
• In a second aspect of the invention, a thin film is applied over the front side and over at least a portion of the outer perimeter. A barrier layer may be applied over the front side and over at least a portion of the outer perimeter, whereupon a further thin film, such as a conductive seed layer, is applied over the barrier layer.[0009]
• After one or more further intervening steps, such as electroplating of a metal layer onto the conductive seed layer, an etchant capable of removing one or more of the thin film layers is caused to flow over an outer margin of the front side while the etchant is prevented from flowing over the front side except for the outer margin. Thus, the etchant only contacts the outer margin of the front side thereby selectively removing only the one or more thin film layers from the outer margin of the front side. If the etchant is also caused to flow over the back side and over the outer perimeter, as well as over the outer margin of the front side, the one or more thin film layers are removed from the outer perimeter and any contaminant that the etchant is capable of removing is stripped from the back side as well. A cleaning chemical can be used instead of an etchant in some applications to remove or dissolve the one or more thin film layers as described above.[0010]
• These and other objects, features, and advantages of this invention are evident from the following description of a preferred mode for carrying out this invention, with reference to the accompanying drawings.[0011]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIGS. 1A, 1B,[0012]1C, and1D are fragmentary, cross-sectional views of a microelectronic workpiece, such as a silicon wafer, at various stages of a known sequence of processing steps in accordance with prior art.
• FIGS. 2A, 2B,[0013]2C, and2D are fragmentary, cross-sectional views of a microelectronic workpiece, such as a silicon wafer, at various stages of a novel sequence of processing steps in accordance with this invention.
• FIGS. 3 and 4 illustrate one embodiment of a reactor that can be used to implement the process of the present invention.[0014]
DETAILED DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION
• Although the process of the present invention has applicability to any process in which a processing fluid is selectively provided to or excluded from an outer margin of a workpiece, the invention will be described in connection with a sequence of processing steps for depositing one or more metallization layers or metallized structures on the workpiece. The known sequence of processing steps in accordance with the prior art begins with a[0015]silicon wafer10, on which microelectronic devices (not shown) have been fabricated. As illustrated in FIG. 1A, thewafer10 has a front,device side12, a back,non-device side14, and a beveled,outer perimeter16. Via physical vapor deposition (sputtering) or chemical vapor deposition, abarrier layer20 is applied over thefront side12 and over anupper portion18 of theouter perimeter16. A thin-film seed layer, such as acopper film30, is applied over thebarrier layer20. Conventionally, theseed layer30 is only deposited within the bounds of anouter margin22 of thebarrier layer20, as illustrated in FIG. 1B. At anouter edge32 of the seed layer, orcopper film30, one or moreelectrical contacts40 to be used in providing electroplating power to the seed layer are placed in electrical contact with thecopper film30, as illustrated in FIG. 1C.
• After the one or more[0016]electrical contacts40 have been connected to the seed layer copper film30 afurther copper layer50 from which interconnect structures and/or metallized devices are fabricated is electroplated onto thewafer10 as illustrated in FIG. 1C. The electrical contact(s)40 are then removed to provide the resultant multi-film structure, shown generally at60 in FIG. 1D. Beyond aninner boundary34 of theouter margin32 of thecopper layer50, anannular region62 of thefront side12 is not available for fabricating such interconnect structures or metallized devices.
• The processing steps of the invention, as shown in FIGS.[0017]2A-2D, begin with asilicon wafer110, which is similar to thesilicon wafer10 before processing, on which microelectronic devices (not shown) have been fabricated, and which has a front,device side112, a back,non-device side114, and a beveled,outer perimeter116. Via physical vapor deposition (sputtering) or chemical vapor deposition, abarrier layer120 is applied over thefront side112 and over anupper portion118 of theouter perimeter116 and a thin seed layer, such as acopper film130 is applied over theentire barrier layer120, without exclusion from a peripheral outer margin, so as to cover thebarrier layer120 where applied over thefront side112 and over theupper portion118 of theouter perimeter116, as illustrated in FIG. 2B. At anouter edge132 of thecopper seed layer130, one or moreelectrical contacts140 to be used in electroplating are connected to provide electroplating power to thecopper film130, as illustrated in FIG. 2C. As illustrated, theouter edge132 at which contact may be made for the supply of electroplating power illustrated in FIG. 2C is substantially closer to the peripheral edge than the process as illustrated in FIG. 1C.
• A[0018]further copper film150 from which metallized interconnects and/or microelectronic devices are fabricated is then applied using an electrochemical deposition process. As illustrated in FIG. 2C, thefurther copper film150 is deposited inside of theouter margin132 of thecopper film130, up to the boundary designated by134. Theelectrical contact140 is then removed leaving the resultant multi-layer structure shown generally at160 of FIG. 2D. Metallized devices (not shown) and/or interconnects are formed by known techniques, from the resultant structure160. After thecopper layer150 has been deposited, theseed layer130,film150, and/orbarrier layer120 may be removed from theouter margin132 and, if desiredperipheral edge116 of theworkpiece110. Removal of at least layer130 from the outer margin assists in preventing film flaking and cross-contamination problems that may occur during subsequent workpiece processing.
• In accordance with the process, a liquid processing fluid is selectively applied to the outer peripheral margin of at least the front side of the workpiece. Exclusion and/or application of the processing fluid occurs by applying one or more processing fluids to the workpiece as the workpiece and corresponding reactor are spinning about an axis of rotation that is generally parallel (or antiparallel) to the vector defining the face of the workpiece being processed. The flow rate of the one or more processing fluids, fluid pressure, and/or spin rate are used to control the extent to which the processing fluid is selectively applied to the outer peripheral margin.[0019]
• A reactor suitable for executing the foregoing removal process may generally be comprised of upper and lower members that define an upper chamber and a lower chamber with respect to the workpiece contained therein. A centrally disposed inlet is provided to each of the upper an lower chambers for supplying one or more processing fluids. Fluid outlets are disposed at peripheral portions of the chambers and are adapted to assist in the exclusion of one processing fluid from the outer margin of the workpiece while allowing intrusion of an etchant thereat. The upper and lower chambers are rotated conjointly so as to distribute a processing fluid in the upper chamber across an upper side of the workpiece through centripetal acceleration and so as to distribute a processing fluid in the lower chamber across a lower side of the workpiece through centripetal acceleration. Depending upon the processes being performed, however, the processing fluids in the upper and lower chambers may be the same fluid or different fluids.[0020]
• Also rather than relying on the rotation of the workpiece, the processing fluid could also be selectively driven by pumps.[0021]
• Through control of the respective pressures of the processing fluids entering the respective chambers and of the rotational speed of the rotating chambers, it is possible to control the reactor so as to cause the processing fluid entering the inlet of the lower chamber to flow over the near side of the wafer, over the outer perimeter of the workpiece, and over an outer margin of the far side of the workpiece, and so as to prevent the same processing fluid from flowing over the far side except for the outer margin. The control of the fluid pressures may be achieved for example through the use of a pump for liquids, or a pressure regulator for a pressurized gas source.[0022]
• The process provided by this invention can be advantageously practiced in a reactor illustrated and described in PCT/US99/05676, 09/113,435 and 60/116,750, incorporated herein by reference.[0023]
• As shown in the FIGS. 3 and 4, a[0024]reactor1100 for processing a microelectronic workpiece, such as asilicon wafer1010 having an upper side1012, a lower side1014, and an outer, circular perimeter1016, in a micro-environment constitutes a preferred platform for the practice of the process of this invention. For certain applications, the upper side1012 is the front side, which may be otherwise called the device side, and the lower side1014 is the back side, which may be otherwise called the non-device side. However, for other applications, thesilicon wafer1010 is inverted.
• Generally, except as disclosed herein, the[0025]reactor1100 is similar to the reactors illustrated and described in U.S. patent application Ser. No. 09/113,435. However, as illustrated in the drawings and described herein, thereactor1100 is improved to be more versatile in executing select microelectronic fabrication processes.
• The[0026]reactor1100 has an upper chamber member or rotor that includes anupper chamber wall1120 and a lower chamber member or rotor that includes alower chamber wall1140. Thesewalls1120,1140, are arranged to open so as to permit awafer1010 to be loaded into thereactor1100 for processing, by a loading and unloading mechanism (not shown) that, for example, may be in the form of a robot having an end effector. Thesewalls1120,1140, are arranged to close so as to define acapsule1160 supporting awafer1010 in a processing position, between thesewalls1120,1140.
• The[0027]reactor1010 has anhead1200 containing arotor assembly1210 supported bybearings1124. Amotor1220 for rotating therotor1210, about a vertical axis A is supported in thehead1200.
• The rotor assembly includes the upper rotor and a lower rotor which can be moved vertically apart, for loading and unlading, and which can be brought together, for processing a wafer. The upper rotor has an[0028]inlet1122 in anupper chamber wall1120 for entry of processing fluids, which may be liquid, vaporous, or gaseous. The lower rotor similarly has alower chamber wall1140 with aninlet1142 for such fluids. Anozzle1212 in thehead1200 extends axially through asleeve1222, so as not to interfere with the rotation of thesleeve1222. Theupper nozzle1212 directs streams of processing fluids downwardly through theinlet1122 of theupper chamber wall1120.
• The[0029]upper chamber wall1120 includes an array ofsimilar outlets1124, which are spaced similarly at uniform angular spacings around the vertical axis A. In the disclosed embodiment, thirty-sixsuch outlets1124 are employed. Theoutlets1124 are spaced radially apart on a circle, with each outlet at the same distance from axis A. The outlets are located near the outside circumference of the rotors, typically about 1.5 mm in from the edge of the rotors.
• When the upper and[0030]lower chamber walls1120,1140, are closed, they define amicro-environment reactor1160 having anupper processing chamber1126 that is defined by theupper chamber wall1120 and by a first generally planar surface of the supportedwafer1010, and alower processing chamber1146 that is defined by thelower chamber wall1140 and a second generally planar surface of the supported wafer opposite the first side. The upper andlower processing chambers1126,1146, are in fluid communication with each other in an annular region1130 beyond theouter perimeter16 of the supportedwafer1010 and are sealed by an annular, compressible seal (e.g. O-ring)1132 bounding a lower portion1134 of the annular region1130. The seal1132 allows processing fluids entering thelower inlet1142 to remain under sufficient pressure to flow toward the outlets1134.
• The reactor[0031]100 is particularly suitable for executing a range of unique microfabrication processes. For example,reactor1100 is particularly suited to execute a process that requires complete contact of a processing fluid at a first side of a workpiece and at only a peripheral margin portion of the second side thereof. Such processes may be realized because processing fluids entering theinlet1142 of thelower chamber wall1140 can act on the lower side1014 of a supportedwafer1010, on the outer periphery1016 of the supportedwafer1010, and on an outer margin1018 of the upper side1012 of the supportedwafer10 before reaching theoutlets1124, and because processing fluids entering theinlet1122 of theupper chamber wall1120 can act on the upper side1012 of the supportedwafer1010, except for the outer margin1018 of the upper side1012, before reaching theoutlets1124.
• When the reactor illustrated and described above is employed to practice the process provided by this invention for treating a silicon wafer having a front, device side, a back, non-device side, and an outer perimeter, so as to remove a thin film, such as a copper film, the silicon wafer is placed into the reactor with its back side being the lower side. An etchant capable of removing the copper is used as the processing. The etchant is delivered by a pump to the lower chamber and inert gas is used as the processing fluid entering the. The etchant is caused to flow over the back side, over an outer perimeter of the silicon wafer, and over an outer margin of the front side, but is prevented from flowing over the front side except for the outer margin. After the etchant removes the thin film, any residual etchant is rinsed away, as with deionized water.[0032]
• The processing fluid can be a mixture of an acid and an oxidizing agent.[0033]
• If the thin film is a metal film, such as a copper film, a preferred etchant is a mixture of hydrofluoric acid and hydrogen peroxide, as an oxidizing agent, most preferably 0.5% hydrofluoric acid and 10% hydrogen peroxide, by volume, with the remainder being deionized water. An alternative reagent is approximately 10% sulfuric acid, although other concentrations of sulfuric acid from approximately 5% to approximately 98%, along with approximately 0% to 20% of an oxidizing agent, can be instead used to remove a metal film, such as a copper film.[0034]
• The processing fluid can also be a mixture of sulfuric acid and amonium persulfate.[0035]
• Other alternative reagents that can be instead used to remove a metal film, such as a copper film, include mixtures of hydrofluoric acid and a surfactant, mixtures of hydrofluoric and hydrochloric acids, mixtures of nitric and hydrofluoric acids, and EKC 5000, which is a proprietary reagent available commercially from EKC of Hayward, Calif.[0036]
• When the resultant structure[0037]160 illustrated in FIG. 2D is compared to theresultant structure60 illustrated in FIG. 1D, it is evident that theannular region162 not available for fabricating such interconnect structures and/or metallized components from the resultant structure160 is smaller than theannular region62 that is not available for fabricating such interconnect structures and/or metallized components on theresultant structure60, all other dimensions being alike. It follows that this invention enables a greater yield of microelectronic devices from a silicon wafer of a given size. Advantageously, the process provided by this invention not only removes a thin film, such as a copper film, but also removes any contaminant, such as any copper or other metal, that the reagent is capable of solvating from the back side of the silicon wafer.
• The thin film removed by the process of the present invention could also be substantially comprised of silicon nitride, silicone oxide, polysilicon, or photoresist.[0038]
• Various modifications can, of course, be made without departing from the scope and spirit of the invention. The invention, therefore, should not be restricted, except by the following claims and their equivalents.[0039]

Claims (9)

1. A process for treating a microelectronic workpiece having a first side, a second side, and an outer perimeter joining the first and second sides at their periphery, the process comprising the steps of:

applying a thin film exterior over the second side and over at least a portion of the outer perimeter;

at a subsequent time, selectively providing a processing fluid capable of removing at least the thin film to flow over an outer margin of the second side while preventing the processing fluid from flowing over the second side except for the outer margin, so as to the substantially remove the thin film from the outer margin of the second side.

2. The process ofclaim 1 wherein the processing fluid is caused to flow over the first side and over the outer perimeter, as well as over the outer margin of the second side, so as to remove the thin film from the outer perimeter and so as to remove any contaminant that the processing is capable of etching or otherwise removing from the first side.

3. The process ofclaim 1 wherein the thin film is substantially comprised of copper.

4. The process ofclaim 1 wherein the-thin film is substantially comprised of a material selected from the group consisting of: silicon nitride, silicon oxide, polysilicon.

5. The process ofclaim 1 wherein the thin film is substantially comprised of photoresist.

6. The process ofclaim 1 wherein the thin film is substantially comprised of a mixture of hydrofluoric acid and hydrogen peroxide.

7. The process ofclaim 1 wherein the thin film is substantially comprised of a mixture of an acid and an oxidizing agent.

8. The process ofclaim 1 wherein the thin film is substantially comprised of mixture of sulfuric acid and hydrogen peroxide.

9. The process ofclaim 1 wherein the thin film is substantially comprised of a mixture of sulfuric acid and amoniun persulfate.

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