Abstract:
A method for supporting a glass substrate comprising providing a substrate support having an aluminum body, a substrate contact area formed on the surface of the substrate support, wherein the process of forming the substrate contact area comprises forming an anodization layer on a surface region of the aluminum body, the coating having a thickness of between about 0.3 mils and about 2.16 mils, wherein the surface region substantially corresponds to the substrate contact area, and preparing the anodization layer disposed over the surface region to a surface roughness between about 88 micro-inches and about 230 micro-inches, followed by anodizing the substrate surface to said thickness, positioning the substrate support adjacent a substrate processing region in a substrate processing chamber, wherein the substrate contact area is adjacent the substrate processing region, positioning the glass substrate on the substrate contact area.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 10/435,182, filed May 9, 2003 now abandoned. 

   BACKGROUND OF THE DISCLOSURE 
   1. Field of the Invention 
   Embodiments of the invention generally provide a substrate support utilized in semiconductor processing and a method of fabricating the same. 
   2. Description of the Background Art 
   Liquid crystal displays or flat panels are commonly used for active matrix displays such as computer and television monitors, personal digital assistants (PDAs), cell phones and the like. Generally, flat panels comprise two glass plates having a layer of liquid crystal material sandwiched therebetween. At least one of the glass plates includes at least one conductive film disposed thereon that is coupled to a power supply. Power supplied to the conductive film from the power supply changes the orientation of the crystal material, creating a pattern such as text or graphics seen on the display. One fabrication process frequently used to produce flat panels is plasma enhanced chemical vapor deposition (PECVD). 
   Plasma enhanced chemical vapor deposition is generally employed to deposit thin films on a substrate such as a flat panel or semiconductor wafer. Plasma enhanced chemical vapor deposition is generally accomplished by introducing a precursor gas into a vacuum chamber that contains a substrate. The precursor gas is typically directed through a distribution plate situated near the top of the chamber. The precursor gas in the chamber is energized (e.g., excited) into a plasma by applying RF power to the chamber from one or more RF sources coupled to the chamber. The excited gas reacts to form a layer of material on a surface of the substrate that is positioned on a temperature controlled substrate support. In applications where the substrate receives a layer of low temperature polysilicon, the substrate support may be heated in excess of 400 degrees Celsius. Volatile by-products produced during the reaction are pumped from the chamber through an exhaust system. 
   Generally, large area substrates utilized for flat panel fabrication are large, often exceeding 550 mm×650 mm, and are envisioned up to and beyond 4 square meters in surface area. Correspondingly, the substrate supports utilized to process large area substrates are proportionately large to accommodate the large surface area of the substrate. The substrate supports for high temperature use typically are casted, encapsulating one or more heating elements and thermocouples in an aluminum body. Due to the size of the substrate support, one or more reinforcing members are generally disposed within the substrate support to improve the substrate support&#39;s stiffness and performance at elevated operating temperatures (i.e., in excess of 350 degrees Celsius and approaching 500 degrees Celsius to minimize hydrogen content in some films). The aluminum substrate support is then anodized to provide a protective coating. 
   Although substrate supports configured in this manner have demonstrated good processing performance, small local variations in film thickness, often manifesting as spots of thinner film thickness, have been observed which may be detrimental to the next generation of devices formed on large area substrates. It is believed that variation is glass thickness and flatness, along with a smooth substrate support surface, typically about 50 micro-inches, creates a local capacitance variation in certain locations across the glass substrate, thereby creating local plasma non-uniformities that results on deposition variation, e.g., spots of thin deposited film thickness. 
   Aging and modifying plasma conditioning of the substrate support has shown to mitigate thin spot formation, particularly when performed in conjunction with an extended chamber vacuum purge before transferring a substrate into the chamber for processing. However, the resultant expenditures of time and materials required by this method and its unfavorable effect on cost and throughput make obtaining a more effective solution desirable. 
   As the size of next generation of substrates continues to grow, the importance of defect reduction becomes increasingly important due to the substantial investment by the flat panel manufacturer represented by each substrate. Moreover, with the continual evolution of device critical dimension reduction demanding closer tolerances for film uniformity, the reduction and/or elimination of film thickness variation becomes an important factor for the economic production of the next generation devices formed on large area substrates. 
   Therefore, there is a need for an improved substrate support. 
   SUMMARY OF THE INVENTION 
   A substrate support and method for fabricating the same are provided. In one embodiment of the invention, a substrate support includes an electrically conductive body having a substrate support surface that is covered by an electrically insulative coating. At least a portion of the coating centered on the substrate support surface has a surface finish of between about 80 to about 200 micro-inches. In another embodiment, a substrate support includes an anodized aluminum body having a surface finish on the portion of the body adapted to support a substrate thereon of between about 80 to about 200 micro-inches. 
   In another embodiment, a substrate support is fabricated by a process including the steps of providing an aluminum body suitable for supporting a large area substrate on a substrate support surface, and forming an anodized coating having a surface roughness of between about 80 to about 200 micro-inches on the substrate support surface. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof that 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  depicts a schematic sectional view of one embodiment of a processing chamber having a substrate support assembly of the present invention; 
       FIG. 2  is a partial sectional view of another embodiment of a substrate support assembly; 
       FIG. 3  is a flow diagram of one embodiment of a method for fabricating a substrate support assembly; 
       FIG. 4  is a flow diagram of another embodiment of a method for fabricating a substrate support assembly; 
       FIG. 5  is a partial sectional view of another embodiment of a substrate support assembly; and 
       FIG. 6  is a partial sectional view of another embodiment of a substrate support assembly. 
   

   To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
   DETAILED DESCRIPTION 
   The invention generally provides a large area substrate support and methods for fabricating the same. The invention is illustratively described below in reference to a plasma enhanced chemical vapor deposition system, such as a plasma enhanced chemical vapor deposition (PECVD) system, available from AKT, a division of Applied Materials, Inc., Santa Clara, Calif. However, it should be understood that the invention has utility in other system configurations such as physical vapor deposition systems, ion implant systems, etch systems, other chemical vapor deposition systems and any other system in which processing a substrate on a substrate support is desired. 
     FIG. 1  is a cross sectional view of one embodiment of a plasma enhanced chemical vapor deposition system  100 . The system  100  generally includes a chamber  102  coupled to a gas source  104 . The chamber  102  has walls  106 , a bottom  108  and a lid assembly  110  that define a process volume  112 . The process volume  112  is typically accessed through a port (not shown) in the walls  106  that facilitates movement of a large area glass substrate  140  into and out of the chamber  102 . The walls  106  and bottom  108  are typically fabricated from an unitary block of aluminum or other material compatible for processing. The lid assembly  110  contains a pumping plenum  114  that couples the process volume  112  to an exhaust port (that is coupled to various pumping components, not shown). 
   The lid assembly  110  is supported by the walls  106  and can be removed to service the chamber  102 . The lid assembly  110  is generally comprised of aluminum. A distribution plate  118  is coupled to an interior side  120  of the lid assembly  110 . The distribution plate  118  is typically fabricated from aluminum. The center section includes a perforated area through which process and other gases supplied from the gas source  104  are delivered to the process volume  112 . The perforated area of the distribution plate  118  is configured to provide uniform distribution of gases passing through the distribution plate  118  into the chamber  102 . 
   A heated substrate support assembly  138  is centrally disposed within the chamber  102 . The support assembly  138  supports the large area glass substrate  140  (herein after “substrate  140 ”) during processing. The substrate support assembly  138  generally includes an electrically conductive body  124  that is covered with an electrically insulative coating  180  over at least the portion of the body  124  that supports the substrate  140 . The coating  180  has a surface finish of about 80 to about 200 micro-inches that has been demonstrated to improve deposition uniformity without expensive aging or plasma treatment of the support assembly  138 . The coating  180  may also cover other portions of the body  124 . It is believed that the rougher surface offsets the effect of glass substrate thickness variation to provide a more uniform capacitance across the substrate, thereby enhancing plasma and deposition uniformity, and substantially eliminating the formation of thin spots in the deposited film. 
   The conductive body  124  may be fabricated from metals or other comparably electrically conductive materials. The coating  180  may be a dielectric material such as oxides, silicon nitride, silicon dioxide, aluminum dioxide, tantalum pentoxide, silicon carbide, polyimide, among others, which may be applied by various deposition or coating processes, including but not limited to, flame spraying, plasma spraying, high energy coating, chemical vapor deposition, spraying, adhesive film, sputtering and encapsulating. 
   In one embodiment, the substrate support assembly  138  includes an aluminum conductive body  124  that encapsulates at least one embedded heating element  132  and a thermocouple. At least a first reinforcing member  116  is generally embedded in the body  124  proximate the heating element  132 . A second reinforcing member  166  may be disposed within the body  124  on the side of the heating element  132  opposite the first reinforcing member  116 . The reinforcing members  116  and  166  may be comprised of metal, ceramic or other stiffening materials. In one embodiment, the reinforcing members  116  and  166  are comprised of aluminum oxide fibers. Alternatively, the reinforcing members  116  and  166  may be comprised of aluminum oxide fibers combined with aluminum oxide particles, silicon carbide fibers, silicon oxide fibers or similar materials. The reinforcing members  116  and  166  may include loose material or may be a pre-fabricated shape such as a plate. Alternatively, the reinforcing members  116  and  166  may comprise other shapes and geometry. Generally, the reinforcing members  116  and  166  have some porosity that allows aluminum to impregnate the members  116 ,  166  during a casting process described below. 
   The heating element  132 , such as an electrode disposed in the support assembly  138 , is coupled to a power source  130  and controllably heats the support assembly  138  and substrate  140  positioned thereon to a predetermined temperature. Typically, the heating element  132  maintains the substrate  140  at an uniform temperature of about 150 to at least about 460 degrees Celsius. 
   Generally, the support assembly  138  has a lower side  126  and an upper side  134  that supports the substrate. The lower side  126  has a stem cover  144  coupled thereto. The stem cover  144  generally is an aluminum ring coupled to the support assembly  138  that provides a mounting surface for the attachment of a stem  142  thereto. 
   Generally, the stem  142  extends from the stem cover  144  and couples the support assembly  138  to a lift system (not shown) that moves the support assembly  138  between an elevated position (as shown) and a lowered position. A bellows  146  provides a vacuum seal between the process volume  112  and the atmosphere outside the chamber  102  while facilitating the movement of the support assembly  138 . The stem  142  additionally provides a conduit for electrical and thermocouple leads between the support assembly  138  and other components of the system  100 . 
   The support assembly  138  generally is grounded such that RF power supplied by a power source  122  to the distribution plate  118  (or other electrode positioned within or near the lid assembly of the chamber) may excite the gases disposed in the process volume  112  between the support assembly  138  and the distribution plate  118 . The RF power from the power source  122  is generally selected commensurate with the size of the substrate to drive the chemical vapor deposition process. 
   The support assembly  138  additionally supports a circumscribing shadow frame  148 . Generally, the shadow frame  148  prevents deposition at the edge of the substrate  140  and support assembly  138  so that the substrate does not stick to the support assembly  138 . 
   The support assembly  138  has a plurality of holes  128  disposed therethrough that accept a plurality of lift pins  150 . The lift pins  150  are typically comprised of ceramic or anodized aluminum. Generally, the lift pins  150  have first ends  160  that are substantially flush with or slightly recessed from an upper side  134  of the support assembly  138  when the lift pins  150  are in a normal position (i.e., retracted relative to the support assembly  138 ). The first ends  160  are generally flared to prevent the lift pins  150  from falling through the holes  128 . Additionally, the lift pins  150  have a second end  164  that extends beyond the lower side  126  of the support assembly  138 . The lift pins  150  may be actuated relative to the support assembly  138  by a lift plate  154  to project from the upper side  134 , thereby placing the substrate in a spaced-apart relation to the support assembly  138 . 
   The lift plate  154  is disposed proximate the lower side  126  of the support surface. The lift plate  154  is connected to the actuator by a collar  156  that circumscribes a portion of the stem  142 . The bellows  146  includes an upper portion  168  and a lower portion  170  that allow the stem  142  and collar  156  to move independently while maintaining the isolation of the process volume  112  from the environment outside the chamber  102 . Generally, the lift plate  154  is actuated to cause the lift pins  150  to extend from the upper side  134  as the support assembly  138  and the lift plate  154  move closer together relative to one another. 
     FIG. 2  is a partial sectional view of one another embodiment of a support assembly  200 . The support assembly  200  includes an aluminum body  202  substantially covered with an anodized coating  210 . The body  202  may be comprised of one or more coupled members or an unitary casted body having the heating element  132  embedded therein. Examples of substrate support assemblies that may be adapted to benefit from the invention are described in U.S. patent application Ser. No. 10/308,385 filed Dec. 2, 2002, and Ser. No. 09/921,104 filed Aug. 1, 2001, both of which are hereby incorporated by reference in there entireties. 
   The body  202  generally includes a substrate support surface  204  and an opposing mounting surface  206 . The mounting surface  206  is coupled to the stem  142  (seen in  FIG. 1 ). The anodized coating  210  covers at least the support surface  204  of the body  202  and provides a separating layer between the substrate  140  and the support surface  204 . 
   The coating  210  includes an outer surface  212  and an inner surface  214 . The inner surface  214  is generally disposed directly on the body  202 . In one embodiment, the anodized coating has a thickness of between about 0.3 to about 2.16 mils. Anodized coatings having a thickness falling outside of this range tend to either fail during temperature cycling or do not sufficiently reduce spotting in SiN, αSi and n+α-Si large area films formed by PECVD deposition. 
   A portion  218  of the outer surface  212  positioned above the substrate support surface  204  has a geometry configured to support the substrate  140  thereon. The portion  218  of the outer surface  212  has a surface finish  216  of a predefined roughness that promotes uniform thickness of films deposited on the substrate  140 . The surface finish  216  has a roughness of about 80 to about 200 micro-inches. The surface finish  216  advantageously results in improved film thickness uniformity and particularly has been found to substantially eliminate local thickness non-uniformity (spots of thin deposition) without conditioning (e.g., aging) the substrate support. The elimination of substrate support conditioning conserves both time and materials normally consumed in a plasma aging process and eliminates vacuum purges between cycles, the elimination of which results in improved system throughput. In one embodiment, the surface finish  216  has a roughness of about 130 micro-inches. 
   The surface finish  216  of the anodized coating  210  may be achieved by treating at least a portion  220  of the outer substrate support surface  204  underlying the substrate  140  and/or by treating at least the anodized coating  210  that supports the substrate  140  (to obtain a pre-defined surface finish  208 ). The surface finish  208  of the substrate support surface  204  may be formed in a number of manners, including bead blasting, abrasive blasting, grinding, embossing, sanding, texturing, etching or other method for providing a pre-defined surface roughness. In one embodiment, the surface finish  208  of the support surface  204  of the body  202  is about 88 to about 230 micro-inches. In another embodiment, the surface finish  208  is about 145 micro-inches. 
   Optionally, a strip  224  of the support surface  204  bounding the portion  220  positioned out from under the substrate  140  may be left untreated to minimize the fabrication costs. This results in a strip  222  of the anodized coating  210  above the untreated strip  224  that may have a finish different than the finish  216 , but as the strip  222  is beyond the substrate  140 , the surface finish of the strip  222  has no effect on film deposition uniformity. In one embodiment, the strip  222  of the anodized coating  210  has a smoother surface finish than the portion  218  of the coating  210  it bounds. 
     FIG. 3  depicts one embodiment of a method  300  for fabricating the support assembly  138 . The method begins at step  302  by preparing the support surface  204  of the body  202 . The preparing step  302  generally entails working or otherwise treating the support surface  204  so that the finish  208  is between about 80 to about 200 micro-inches. In one embodiment, the preparing step  302  may include bead blasting, abrasive blasting, grinding, embossing, sanding, texturing, etching or other method for providing a pre-defined surface roughness, for example, about 130 micro-inches. 
   In one embodiment, the substrate support surface  204  is bead blasted to a pre-determined surface finish. Bead blasting may include impacting the body  202  with a ceramic or oxide bead. 
   In another embodiment, the bead is aluminum oxide, having an average diameter of about 125 to about 375 micron. The beads are provided through a nozzle having an exit velocity sufficient to produce a surface finish  208  of about 88 to about 230 micro-inches. 
   After the completion of the preparing step  302 , the body is anodized at step  304 . The anodizing step  304  generally includes applying an anodized layer having a thickness between about 0.3 to about 2.16 mils. The resultant surface finish  216  on the outer surface  212  of the anodized coating  212  is about 80 to about 200 micro-inches, and in one embodiment is about 130 micro-inches. 
     FIG. 4  depicts another embodiment of a method  400  of fabricating a support assembly  138 . The method begins at step  402  by anodizing the aluminum body  202 . At step  404 , at least a portion  218  of the outer surface  212  of the anodized coating  210  is treated to provide a roughened surface finish  216 . Alternatively, other portions of the outer surface  212  may be treated. 
   The treating step  404  may include bead blasting, abrasive blasting, grinding, embossing, sanding, texturing, etching or other method for providing a pre-defined surface roughness. In one embodiment, the treating step  404  results in a surface finish of the outer surface of about between about 80 to about 200 micro-inches. 
     FIG. 5  depicts a partial sectional view of another embodiment of a support assembly  500  configured to enhance uniform deposition thickness. The support assembly  500  includes an aluminum support body  502  substantially encapsulated by an anodized coating  506 . A heating element  504  is coupled to the support body  502  to control the temperature of the substrate  140  positioned on the upper surface of the support assembly  500 . The heating element  504  may be a resistive heater or other temperature control device coupled to or disposed against the body  502 . Alternatively, a lower portion  512  of the body  502  may be free from anodization to provide direct contact between the heating element  504  and the body  502 . Optionally, an intervening layer (not shown) of thermally conductive material may be disposed between the heating element  504  and the lower portion  512  of the body  502 . 
   An upper portion  508  of the anodized coating  506  that supports the substrate  140  has a surface finish  510  configured to enhance uniform deposition of films on the substrate  140 . In one embodiment, the surface finish  510  has a roughness between about 80 to about 200 micro-inches. The surface finish  510  may be created through a number of methods, including the methods described above. 
     FIG. 6  depicts another embodiment of a heater assembly  600 . The heater assembly  600  includes an aluminum body  602  having an anodized coating  606  at least partially formed thereon. A heating element  604 , i.e., a conduit through which a temperature-controlled fluid is circulated, is disposed against a bottom surface of the body  602  to facilitate temperature control of the substrate  140 . Optionally, a thermally conductive plate  614  may be disposed between the heating element  604  and the body  602  in order to enhance temperature uniformity between the heating element  604  and the body  602 . In one embodiment, the intervening layer  614  is a copper plate. 
   A clamp plate  608  is coupled to the body  602  by a plurality of fasteners  610  (one of which is shown in  FIG. 6 ) that thread into a threaded hole  612  formed in the body  602 . The clamp plate  608  sandwiches the heating element  604  with the body  602 , thereby enhancing heat transfer. 
   A portion  620  of the anodized coating  606  that supports the substrate  140  has a surface finish  622  configured to enhance uniform deposition of films on the substrate  140 . The surface finish  622  may be created similar to that described above. 
   Thus, a support assembly that enhances uniform deposition of films disposed on a large area substrate is provided. At least a portion of an anodized coating covering the aluminum body of the support assembly which supports the substrate is textured to a pre-determined surface roughness that enhances deposition uniformity, thereby substantially eliminating time-consuming aging of the support assembly and its associated costs. 
   Although several preferred embodiments which incorporate the teachings of the present invention have been shown and described in detail, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.