US20140345803A1 - Method and apparatus for stable plasma processing - Google Patents

Abstract

A method and apparatus for etching a substrate using a spatially modified plasma is provided herein. In one embodiment, the method includes providing a process chamber having a plasma stabilizer disposed above a substrate support pedestal. A substrate is placed upon the pedestal. A process gas is introduced into the process chamber and a plasma is formed from the process gas. The substrate is etched with a plasma having an ion density to radical density ratio defined by the plasma stabilizer.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation of copending U.S. patent application Ser. No. 13/734,532, filed Jan. 4, 2013, to be issued on Aug. 12, 2014, as U.S. Pat. No. 8,801,896, which is a continuation of copending U.S. patent application Ser. No. 10/880,754, filed Jun. 30, 2004, and issued as U.S. Pat. No. 8,349,128, which issued on Jan. 8, 2013, each of which is incorporated herein by reference. The subject matter of this application is related to the subject matter disclosed in pending U.S. patent application Ser. No. 14/050,224, entitled “METHOD AND APPARATUS FOR PHOTOMASK PLASMA ETCHING”, filed on Oct. 9, 2013, with priority to Jun. 30, 2004, by Kumar, et al. (ATTORNEY DOCKET NUMBER 9400.C2).
FIELD
• Embodiments of the present invention generally relate to a method and apparatus for plasma processing of a substrate and, more specifically, to a method and apparatus for etching a substrate using a stable plasma.
BACKGROUND
• Integrated circuits have evolved into complex devices that can include millions of transistors, capacitors and resistors on a single chip. The evolution of chip designs continually requires faster circuitry and greater circuit density. Circuit density has a pronounce importance as the speed and number of functions a circuit can execute increases along with the density of the circuit structure. Some design attributes affecting the speed and circuit density of integrated circuits include the resistance and thickness of the materials used to form the layer comprising the circuit structure formed on a substrate.
• Metallic materials are used to create wireline interconnects, vias, electrodes, and the like. The metal structures are key to the functionality of an integrated circuit. One metal that is frequently used to fabricate circuit structures is tungsten. Tungsten may be accurately deposited using conventional Chemical Vapor Deposition (CVD) methods and generally has a low resistivity. Circuit designers have found tungsten to be a favorable material for use proximate polysilicon as tungsten exhibits good resistance to permeation by polysilicon, which enables tungsten to retain its physical properties over the course of substrate processing and device use.
• In order to maximize circuit density, the layers comprising the circuit structure, including those comprising tungsten, must be minimized. However, when processing such thin layers, care must be taken to avoid damaging the layers during processing. Damaged layers result in defective circuit structures and increased substrate rejects.
• One process that can easily damage thin layers is etching. Fluorinated chemistry is typically employed to remove exposed tungsten and other metals. A plasma is utilized to enhance the etch process. However, it is difficult to maintain a stable plasma. One method for increasing plasma stability is to increase the power supplied to the chamber. Another method is to decrease the gap between the substrate being etched and the top of the chamber. Unfortunately, both increasing the power and decreasing the gap lead to an increase in ion bombardment of the substrate, which may seriously damage the circuits being formed on the substrate.
• Therefore, there is a need in the art for an improved method and apparatus for etching metals, especially tungsten.
SUMMARY
• The present invention generally provides a method and apparatus for etching a substrate using a spatially modified plasma. In one embodiment, the method includes providing a process chamber having a plasma stabilizer disposed above a substrate support pedestal. A substrate is placed upon the pedestal. A process gas is introduced into the process chamber and a quasi-remote plasma is formed from the process gas. The substrate is etched with a plasma having an ion density to radical density ratio defined by the plasma stabilizer.
• In another embodiment of the invention, an apparatus is provided for etching a substrate with a spatially modified plasma. The apparatus includes a process chamber having a substrate support pedestal disposed therein. An RF power source is provided for forming a plasma within the chamber. A plasma stabilizer is disposed in the chamber above the pedestal. The plasma stabilizer controls the spatial distribution of charged and neutral species of the plasma. The plasma stabilizer includes a substantially flat member electrically isolated from the chamber. The member has a plurality of apertures formed therethrough.
BRIEF DESCRIPTION OF THE DRAWINGS
• So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
• FIG. 1 is a schematic diagram of an etch reactor having a plasma stabilizer;
• FIG. 2 is a partial perspective view of one embodiment of the plasma stabilizer ofFIG. 1; and
• FIG. 3 is a flow chart of a method of etching tungsten.
DETAILED DESCRIPTION
• The present invention provides a method and apparatus for improved etching processes. The apparatus includes a plasma stabilizer disposed in a plasma processing chamber. The plasma stabilizer controls the spatial distribution of the charged and neutral species in the chamber during processing such that a dense, stable plasma may be formed in an upper processing region of the chamber (above the plasma stabilizer) and a plasma with controlled characteristics in a lower processing region (between the plasma stabilizer and a substrate disposed on a substrate support pedestal).
• FIG. 1 depicts a schematic diagram of anetch reactor100 having aplasma stabilizer170. Suitable reactors that may be adapted for use with the teachings disclosed herein include, for example, the Decoupled Plasma Source (DPS®) I and DPS® II reactors, all of which are available from Applied Materials, Inc. of Santa Clara, Calif. The DPS® I and DPS® II reactors may also be used as processing modules of a Centura® integrated semiconductor wafer processing system, also available from Applied Materials, Inc. The particular embodiment of thereactor100 shown herein is provided for illustrative purposes and should not be used to limit the scope of the invention.
• Thereactor100 generally comprises aprocess chamber102 having asubstrate pedestal124 within a conductive body (wall)104, and acontroller146. Thechamber102 has a substantially flatdielectric ceiling108. Other modifications of thechamber102 may have other types of ceilings, e.g., a dome-shaped ceiling. Anantenna110 is disposed above theceiling108. Theantenna110 comprises one or more inductive coil elements that may be selectively controlled (twoco-axial elements110aand110bare shown inFIG. 1). Theantenna110 is coupled through a first matchingnetwork114 to aplasma power source112. Theplasma power source112 is typically capable of producing up to about 3000 W at a tunable frequency in a range from about 50 kHz to about 13.56 MHz.
• The substrate pedestal (cathode)124 is coupled through asecond matching network142 to a biasingpower source140. The biasingsource140 generally is a source of up to about 500 W at a frequency of approximately 13.56 MHz that is capable of producing either continuous or pulsed power. Alternatively, thesource140 may be a DC or pulsed DC source.
• In one embodiment, thesubstrate support pedestal124 comprises anelectrostatic chuck160. Theelectrostatic chuck160 comprises at least oneclamping electrode132 and is controlled by achuck power supply166. In alternative embodiments, thesubstrate pedestal124 may comprise substrate retention mechanisms such as a susceptor clamp ring, a mechanical chuck, and the like.
• Alift mechanism138 is used to lower or raise the substrate122 onto or off of thesubstrate support pedestal124. Generally, thelift mechanism162 comprises a plurality of lift pins130 (one lift pin is shown) that travel through respective guide holes136.
• In operation, the temperature of the substrate122 is controlled by stabilizing the temperature of thesubstrate pedestal124. In one embodiment, thesubstrate support pedestal124 comprises aresistive heater144 and aheat sink128. Theresistive heater144 generally comprises at least oneheating element134 and is regulated by aheater power supply168. A backside gas (e.g., helium (He)) from agas source156 is provided via agas conduit158 to channels that are formed in the pedestal surface under the substrate122. The backside gas is used to facilitate heat transfer between thepedestal124 and the substrate122. During processing, thepedestal124 may be heated by the embeddedresistive heater144 to a steady-state temperature, which in combination with the helium backside gas, facilitates uniform heating of the substrate122. Using such thermal control, the substrate122 may be maintained at a temperature between about 0 and 350 degrees Celsius.
• Aplasma stabilizer170 is disposed in thechamber102 above thepedestal124. Theplasma stabilizer170 controls the spatial distribution of the charged and neutral species in thechamber102 during processing such that a dense, stable plasma may be formed in an upper processing region of the chamber (above the plasma stabilizer170) and a plasma with controlled characteristics in a lower processing region (between theplasma stabilizer170 and a substrate122 disposed on a substrate support pedestal124).
• Theplasma stabilizer170 is electrically isolated from thechamber walls104 and thepedestal124 and generally comprises a substantiallyflat plate172 and a plurality oflegs176. Theplate172 is supported in thechamber102 above thepedestal124 by thelegs176. Theplate172 defines one or more openings (apertures) that define a desired open area in the surface of theplate172. The open area of theplasma stabilizer170 controls the quantity of ions that pass from a plasma formed in anupper process volume178 of theprocess chamber102 to alower process volume180 located between theplasma stabilizer170 and the substrate122. Thus, the open area of theplasma stabilizer170 controls the spatial distribution of charged and neutral species of the plasma in theprocess chamber102. The greater the open area, the more ions can pass through theplasma stabilizer170. As such, the size of theapertures174 affects the ion density involume180.
• Theapertures174, or open area, of theplasma stabilizer170 also affect the amount of etch by-products created on the surface of the substrate122 from diffusing into theupper process volume178 of theprocess chamber102 where the RF power is being deposited into the plasma. The size of theaperture174 is chosen to allow sufficient ions and radicals created in theupper process volume178 to reach the surface of the substrate122 and to prevent etch by-products from significantly destabilizing the deposition of RF power into the plasma.
• In addition, the greater the open area, the more uniform the spatial distribution of the charged and neutral species of the plasma becomes. A larger open area also reduces the stability of the plasma. Thus, by controlling the open area of theplasma stabilizer170, the stability of the plasma is controlled. In addition, the spatial distribution of charged and neutral species in the upper andlower processing volumes178,180 is controlled, thereby controlling etch uniformity and selectivity.
• FIG. 2 depicts one specific embodiment of theplasma stabilizer170. In this embodiment, theplasma stabilizer170 includes aplate172 having one ormore apertures174 and a plurality oflegs176. Theplate172 should be thick enough to be robust and thin enough to prevent the ions formed in the plasma from recombining. Theplate172 may be fabricated of a ceramic (such as alumina), quartz, anodized aluminum, or other materials compatible with process chemistries and conditions. In another embodiment, theplate172 could comprise a screen or a mesh wherein the open area of the screen or mesh corresponds to the desired open area provided by the one ormore apertures174. Alternatively, a combination of a plate and screen or mesh may also be utilized.
• The one ormore apertures174 may vary in size, spacing and geometric arrangement across the surface of theplate172 to obtain a desired open area. Theapertures174 should be large enough to allow the plasma to sufficiently penetrate through theplate172 and may be arranged to define an open area in the surface of theplate172 of from about 2 percent to about 90 percent. In one embodiment, theapertures174 are greater than 0.2 inches (0.51 cm) in diameter. In one embodiment, the one ormore apertures174 includes a plurality of approximately half-inch (1.25 cm) diameter holes arranged in a square grid pattern. It is contemplated that the holes may be arranged in other geometric or random patterns utilizing other size holes or holes of various sizes. In another embodiment, the one or more apertures220 may comprise a single aperture220. In one embodiment, the single aperture220 may be substantially the same size and shape of the substrate614 disposed on the pedestal616.
• The size, shape and patterning of the holes may vary depending upon the desired ion density in thelower process volume180. For example, more holes of small diameter may be used to increase the radical to ion density ratio in thevolume180. In other situations, the holes may be made larger, or a number of larger holes may be interspersed with small holes to increase the ion density to radical density ratio in thevolume180. Alternatively, the larger holes may be positioned in specific areas of theplate172 to contour the ion distribution in thevolume180. It is also contemplated that the holes are not perpendicular to the surface of the plate, i.e., they may be angled.
• The height at which theplasma stabilizer170 is supported may vary to further control the etch process. The closer theplasma stabilizer170 is located to theceiling108, the smaller theupper process volume178. A smallupper process volume178 promotes a more stable plasma. In one embodiment, theplasma stabilizer170 is disposed approximately 1 inch (2.54 cm) from theceiling108. A faster etch rate may be obtained by locating theplasma stabilizer170 closer to thepedestal124 and, therefore, the substrate122. Alternatively, a lower, but more controlled, etch rate may be obtained by locating theplasma stabilizer170 farther from thepedestal124. In one embodiment, theplasma stabilizer170 is disposed approximately 2 inches from thepedestal124. Alternatively, theplasma stabilizer170 may have a contoured shape to be closer to theceiling108 in certain areas and farther in others, thereby shaping theupper volume178 of theprocess chamber102 in a desired manner to control the shape or contour of the plasma.
• To maintain theplate172 in a spaced-apart relationship with respect to the substrate122, theplate172 is supported by a plurality oflegs176 disposed on thepedestal124. Thelegs176 are generally located around an outer perimeter of thepedestal124 or theedge ring126 and may be fabricated of the same materials as theplate172. In one embodiment, threelegs176 may be utilized to provide a stable support for theplasma stabilizer170. Thelegs176 generally maintain theplate172 in a substantially parallel orientation with respect to the substrate122 orpedestal124. However, it is contemplated that an angled orientation may be used by havinglegs176 of varied lengths.
• An upper end of thelegs176 may be press fit into a corresponding hole formed in theplate172. Alternatively, the upper end of thelegs176 may be threaded into theplate172 or into a bracket secured to an underside of theplate172. Other conventional fastening methods not inconsistent with processing conditions may also be used to secure thelegs176 to theplate176.
• Thelegs176 may rest on thepedestal124 or theedge ring126. Alternatively, thelegs176 may extend into a receiving hole (not shown) formed in thepedestal124 oredge ring126. Other fastening methods are also contemplated for securing theplasma stabilizer170 to thepedestal124 oredge ring126, such as by screwing, bolting, bonding, and the like. When secured to theedge ring126, theplasma stabilizer170 may be part of an easily-replaceable process kit for ease of use, maintenance, replacement, and the like. It is contemplated that theplasma stabilizer170 may be configured to be easily retrofitted in existing process chambers.
• Alternatively, theplate172 may be supported above thepedestal124 by other means such as by using a bracket (not shown) attached to thewall104 or other structure within theprocess chamber102—as long as theplate172 is insulated from the ground path.
• Returning toFIG. 1, one or more process gases are provided to theprocess chamber102 from agas panel120. The process gases are typically supplied through one or more inlets116 (e.g., openings, injectors, and the like) located above thesubstrate pedestal124. In the embodiment depicted inFIG. 1, the process gases are provided to theinlets116 using anannular gas channel118. Thegas channel118 may be formed in thewall104 or in gas rings (as shown) that are coupled to thewall104. During an etch process, the process gases are ignited into a plasma by applying power from theplasma source112 to theantenna110.
• The pressure in thechamber102 is controlled using athrottle valve162 and avacuum pump164. The temperature of thewall104 may be controlled using liquid-containing conduits (not shown) that run through thewall104. Typically, thechamber wall104 is formed from a metal (e.g., aluminum, stainless steel, and the like) and is coupled to anelectrical ground106. Theprocess chamber102 also comprises conventional systems for process control, internal diagnostic, end point detection, and the like. Such systems are collectively shown assupport systems154.
• Thecontroller146 comprises a central processing unit (CPU)644, amemory148, and supportcircuits152 for theCPU150 and facilitates control of the components of theprocess chamber102 and, as such, of the etch process, as discussed below in further detail. Thecontroller146 may be one of any form of general-purpose computer processor that can be used in an industrial setting for controlling various chambers and sub-processors. The memory, or computer-readable medium, 642 of theCPU150 may be one or more of readily available memory such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or any other form of digital storage, local or remote. Thesupport circuits152 are coupled to theCPU150 for supporting the processor in a conventional manner. These circuits include cache, power supplies, clock circuits, input/output circuitry and subsystems, and the like. The inventive method is generally stored in thememory148 as a software routine. Alternatively, such software routine may also be stored and/or executed by a second CPU (not shown) that is remotely located from the hardware being controlled by theCPU150.
• Oneexemplary method300 for using theplasma stabilizer170 to etch a layer of tungsten disposed on a substrate is depicted in the flow chart ofFIG. 3 and illustrated with respect toFIG. 1. Themethod300 begins atstep302 where a substrate122 is placed in aprocess chamber102 on asupport pedestal124 beneath aplasma stabilizer170. The substrate122 is generally a semiconductor substrate having an at least partially exposed layer of tungsten disposed thereon. A bias power of from about 0 to about 200 W may be applied by thebias power source140 to theelectrostatic chuck160 to assist in retaining thesubstrate124 in place on thepedestal124 during processing. In one embodiment, about 50 W of bias power is applied. Although tungsten is described as one example of a material that can be beneficially etched using theplasma stabilizer170 of the present invention, other materials, especially metals, can also be beneficially etched using thestabilizer170 and the quasi-remote plasma generated thereby.
• Atstep304, a process gas is introduced into theprocess chamber102. The process gas may be sulfur hexafluoride (SF₆) and may also include nitrogen (N₂). The SF₆may be provided at a rate of from about 20 to about 300 standard cubic centimeters per minute (sccm). In one embodiment, SF₆is provided at a rate of about 48 sccm. The N₂may be provided at a rate of from about 0 to about 30 sccm. In one embodiment, the N₂is provided at a rate of about 12 sccm. Other suitable process gases for etching include chlorine (Cl₂), nitrogen trifluoride (NF₃), carbon tetrafluoride (CF₄), hydrogen chloride (HCl), and the like. These process gases may be provided in similar ranges as the SF₆and may also be part of a gaseous compound or introduced along with other process gases, such as N₂. The pressure inside theprocess chamber102 is generally controlled to be within the range of from about 3 to about 50 mTorr. In one embodiment, the pressure inside theprocess chamber102 is controlled to be about 10 mTorr.
• Atstep306, a plasma is formed in thechamber102 by applying RF power from theplasma power source112 to theantenna110. Power is typically provided in a range of from about 100 to about 1200 W. In one embodiment, RF power at a power level of about 600 W is applied to theantenna110 at a frequency of about 13.56 MHz.
• When the plasma is formed duringstep306, theplasma stabilizer170 provides for a dense, stable plasma in theupper process volume178. Thus, enabling the substrate122 to be etched at lower pressures and power requirements. Specifically, plasma stability measurements taken over a blanket tungsten substrate in etch chambers not containing theplasma stabilizer170 have revealed that, over a range of pressures of from about 0 to about 60 mTorr, RF power of about 1500 W and higher was required to maintain a stable plasma. At pressures in the range of from about 10 to about 30 mTorr, significantly higher power was required to stabilize the plasma, and in some cases, the plasma was not able to be stabilized even at power levels in excess of 3000 W. A similar set of plasma stability measurements were taken in the same chamber, but with aplasma stabilizer170 installed. Using theplasma stabilizer170, the plasma was found to be stable over a range of pressures from about 0 to about 60 mTorr at about 500 W of RF power. Thus, use of theplasma stabilizer170 widens the process window, enabling etch processes at pressures and power levels previously unattainable. Furthermore, the more stable plasma, in combination with the control of the spatial distribution of the charged and neutral species in the upper andlower processing volumes178,180, improves etch uniformity and selectivity.
• For other plasma processing applications, by-products created by the processing of the substrate may detrimentally affect the process results. For example, when etching chrome using a chlorine and oxygen plasma, the chrome-oxy-chloride etch by-product generated by the substrate can become dissociated by the plasma, which then inhibits the etching process. In this application, use of the plasma stabilizer prevents the etch by-products from traveling to the region where the RF power is being deposited and thereby improves the uniformity and selectivity of the chrome etch process.
• Similar improvements in the stability and uniformity of other plasma processing applications such as CVD, PVD, gate nitridation, and plasma implant could be achieved by using a plasma stabilizer structure as described above.
• While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims (20)

1. An apparatus for plasma processing a substrate, comprising:

a plasma processing chamber;

a substrate support pedestal disposed in the plasma processing chamber;

an inductive antenna for forming a plasma within the plasma processing chamber;

a plasma stabilizer member disposed in the plasma processing chamber above the substrate support pedestal, the plasma stabilizer member electrically isolated from the plasma processing chamber and having a diameter greater than a diameter of the pedestal and a plurality of apertures formed through the member; and

a plurality of support legs supporting the plasma stabilizer member above the substrate support pedestal; and

an edge ring disposed on the substrate support pedestal and having the plurality of support legs extending from the edge ring, wherein the plasma stabilizer member is secured to the edge ring.

2. The apparatus ofclaim 1, wherein the antenna inductively couples RF power to the plasma processing chamber.

3. The apparatus ofclaim 1, wherein the plasma stabilizer member is disposed about 1.25 cm below a ceiling of the plasma processing chamber.

4. The apparatus ofclaim 1, wherein the plurality of apertures is arranged in a square grid pattern.

5. The apparatus ofclaim 1, wherein the apertures are about 1.25 cm in diameter.

6. The apparatus ofclaim 1, wherein the plasma stabilizer member is non-parallel to the upper surface of the substrate support pedestal.

7. The apparatus ofclaim 1, wherein the apertures have a hole size, shape, position, and distribution over the surface of the plasma stabilizer member to define an ion density to radical density ratio proximate the substrate support pedestal.

8. The apparatus ofclaim 1, wherein the edge ring is disposed about an upper portion of the substrate support pedestal.

9. The apparatus ofclaim 1, wherein the legs support the plasma stabilizer member in a substantially parallel, spaced apart relation with respect to the substrate support pedestal.

10. The apparatus ofclaim 1, wherein the plasma stabilizer member is fabricated from at least one of ceramic, quartz, or anodized aluminum.

11. The apparatus ofclaim 1, wherein the plasma stabilizer member is electrically isolated from ground.

12. The apparatus ofclaim 1, wherein the plasma stabilizer member is operable to form a plasma having an ion density to radical density ratio in a first region above the plasma stabilizer member that is different from the ion density to radical density in a second region below the plasma stabilizer member.

13. The apparatus ofclaim 12, wherein the ion density to radical density ratio is lower in the second region.

14. An apparatus for plasma etching, comprising:

a process chamber;

a substrate support disposed in the process chamber, wherein the substrate support comprises an edge ring;

an inductive antenna for forming a plasma within the process chamber;

a member secured to the edge ring and having a diameter greater than a diameter of the substrate support and a plurality of apertures, wherein the member is electrically isolated from the process chamber; and

a plurality of support legs extending from the edge ring and maintaining the member in a spaced apart relation to the substrate support.

15. The apparatus ofclaim 14, wherein the antenna inductively couples RF power to the process chamber.

16. The apparatus ofclaim 14, wherein the plurality of apertures comprises a first group of apertures arranged in a first aperture density and a second group of apertures arranged in a second aperture density that is different than the first aperture density.

17. The apparatus ofclaim 15, wherein the legs maintain the member in a substantially parallel relation with respect to the substrate support.

18. The apparatus ofclaim 16, wherein the plasma has an ion density to radical density ratio in a first region above the member that is different from the ion density to radical density in a second region below the member.

19. The apparatus ofclaim 17, wherein the member is fabricated from at least one of ceramic, quartz, or anodized aluminum.

20. The apparatus ofclaim 18, wherein the apertures are arranged in a square grid pattern.

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