Abstract:
An article having a protective coating for use in semiconductor applications and method for making the same is provided. In one embodiment, a method of coating an aluminum surface of an article utilized in a semiconductor deposition chamber includes the steps of heating a coating material to a semi-liquidous state, the coating material comprising at least one material from the group consisting of aluminum fluoride and magnesium fluoride and depositing the heated coating material on the aluminum surface. The protective coating has a beta phase grain orientation of less than about 10 percent that has good adhesion to aluminum and resists cracking, flaking and peeling. Some articles that may be advantageously coated include showerheads, blocker plates, support assemblies and vacuum chamber bodies, among others.

Description:
FIELD OF THE INVENTION 
     Embodiments of the invention generally relate to an article having a protective coating for use in a semiconductor processing chamber and a method of making the same. 
     BACKGROUND OF THE INVENTION 
     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 that demand increasingly precise fabrication techniques and processes. One fabrication process frequently used is chemical vapor deposition (CVD). 
     Chemical vapor deposition is generally employed to deposit a thin film on a substrate or a semiconductor wafer. Chemical vapor deposition is generally accomplished by introducing a precursor gas into a vacuum chamber. The precursor gas is typically directed through a showerhead situated near the top of the chamber. The precursor gas reacts to form a layer of material on the surface of the substrate that is positioned on a heated substrate support typically fabricated from aluminum. Purge gas is routed through holes in the support to the edge of the substrate to prevent deposition at the substrate&#39;s edge that may cause the substrate to adhere to the support. Deposition by-products produced during the reaction are pumped from the chamber through an exhaust system. One material frequently formed on substrates using a chemical vapor deposition process is tungsten. A precursor gas that may be used to form tungsten generally includes tungsten hexafluoride (WF 6 ) and silane. As the silane and tungsten hexafluoride mix, some “stray” tungsten (i.e., tungsten that does not deposit on the substrate) deposits on the showerhead and other chamber components. The stray tungsten film builds on the showerhead and may become a source of contamination in the chamber. Eventually, the stray tungsten may clog the holes in the showerhead that facilitate passage of the precursor gas therethrough and necessitating the showerhead be removed and cleaned or replaced. 
     To extend the interval of time between routine maintenance of the showerhead, fluorine-based chemistries are generally used to clean (i.e., etch away) the stray tungsten film. However, the use of fluorine, while advantageous for removing tungsten, reacts to form a layer of aluminum fluoride on the heated support and other surfaces that are made of aluminum, a material commonly used in CVD chambers. The aluminum fluoride layer formed in this manner has a generally rough surface topography. The rough surface of an aluminum fluoride layer on the heated aluminum support creates a leak path that impairs the vacuum used to chuck or hold the substrate to the heated support. Additionally, the aluminum fluoride layer often cracks and peels over the course of thermal cycling of the heated support, and thus becomes a source of particulate contamination. 
     One solution to the formation of aluminum fluoride on heated aluminum supports is to fabricate the heater from ceramic materials that are resistant to fluorine. However, ceramic supports are difficult to fabricate and, consequently, are very costly as compared to conventional aluminum heaters used in CVD processes. 
     Another way to prevent fluorine reaction with the aluminum support is to deposit an aluminum fluoride barrier layer on the support. However, conventional methods of applying aluminum fluoride to the support result in aluminum fluoride barrier layers having about 20 to about 30 percent of the grain structure in the beta phase and about 70 to about 80 percent of the grain structure in the alpha phase. Aluminum fluoride layers having greater than about 10 percent of the grain structure in the beta phase do not adhere well to aluminum and are also prone to cracking. As the aluminum fluoride barrier layer cracks, fluorine, reacting with the underlying aluminum, causes additional growth of aluminum fluoride under the layer, eventually causing the barrier layer of aluminum fluoride to separate from the support. Flakes of aluminum fluoride from the peeled barrier layer are a source of particulate contamination which is detrimental to process yields. Other aluminum surfaces within the processing chamber have similar problems. 
     Therefore, there is a need for coating that protects aluminum surfaces in semiconductor processing chambers. 
     SUMMARY OF THE INVENTION 
     An article having a protective coating for use in semiconductor applications and method for making the same is provided. In one aspect, an article for use in a semiconductor processing chamber includes a coating comprising an aluminum fluoride or a magnesium fluoride layer applied in a semi-liquid, semi-solid state to the aluminum surface of a chamber component. 
     In another aspect, a substrate support is provided having a protective coating. In one embodiment, the substrate support includes a support body having a heating element disposed therein. A coating comprising an aluminum fluoride or magnesium fluoride layer is applied to an aluminum surface of the support body in a semi-liquid, semi-solid state. 
     In another aspect, a method of coating an aluminum surface of an article utilized in a semiconductor deposition chamber is provided. In one embodiment, a method of coating an aluminum surface of an article utilized in a semiconductor deposition chamber includes the steps of heating a coating material to a semi-liquid, semi-solid state, the coating material comprising at least one material from the group consisting of aluminum fluoride and magnesium fluoride and depositing the heated coating material on the aluminum surface. The protective coating has a beta phase grain orientation of less than about 10 percent that provides good adhesion to aluminum and resists cracking, flaking and peeling. Some articles that may be advantageously coated using this method include showerheads, blocker plates, support assemblies and vacuum chamber bodies among others. 
     In another aspect, a method of coating an aluminum surface on a substrate support includes the steps of forming a plasma from an inert gas, heating aluminum fluoride with the plasma, and spraying the heated aluminum fluoride on the aluminum 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 which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of the invention and are, therefore, not to be considered limiting in 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 heater assembly disposed therein; 
     FIG. 2 depicts a partial sectional view of one embodiment of the heater assembly depicted in FIG. 1; 
     FIG. 3 depicts a top view of the heater assembly depicted in FIG. 2; 
     FIG. 4 depicts a flow diagram of one embodiment of a method of fabricating a heater assembly; 
     FIG. 5 depicts a flow diagram of another embodiment of a method of fabricating a heater assembly; and 
     FIG. 6 depicts a partial sectional view of another embodiment of a heater assembly. 
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention generally provides a processing system having coated aluminum surfaces that is advantageous for the deposition of tungsten and other films. The invention is illustratively described below as a chemical vapor deposition system, such as a WxZ™ metal chemical vapor deposition (MCVD) system, available from Applied Materials, Inc. of Santa Clara, Calif. However, it should be understood that while the invention has particular utility for protecting aluminum surfaces of substrate supports against reactions with fluorine and fluorine comprising fluids, the invention is contemplated for use on substrate supports utilized on other deposition systems, etch systems and other surfaces within semiconductor processing chambers. It should be noted that the term aluminum used herein is intended to include aluminum and its alloys. 
     FIG. 1 is a cross-sectional view of one embodiment of a 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  110  that define a process volume  112 . The walls  106  and bottom  108  are typically fabricated from a unitary block of aluminum. The chamber  102  contains a pumping ring  114  that couples the process volume  112  to an exhaust port  116 . The exhaust port  116  is coupled to various pumping components (not shown) that exhaust and control the pressure within the process volume  112 . 
     The lid  110  is supported by the walls  106  and can be removed to service the chamber  102 . The lid  110  is generally comprised of aluminum and may additionally contain heat transfer fluid channels for regulating the temperature of the lid  110  by flowing a heat transfer fluid therethrough. 
     A showerhead  118  is coupled to an interior side  120  of the lid  110 . The showerhead  118  is typically fabricated from aluminum. The showerhead  118  generally includes a perimeter mounting ring  122  that surrounds a “dish-shaped” center section  124 . The mounting ring  122  includes a plurality of mounting holes  126  that pass therethrough, each accepting a vented mounting screw  128  that threads into a mating hole  130  in the lid  110 . The center section  124  includes a perforated area  132  that facilitates passage of gases therethrough. 
     A mixing block  134  is disposed in the lid  110 . The mixing block  134  is coupled to the gas source  104 , such that process and other gases may be introduced to the process volume  112  by passing through the mixing block  134  and showerhead  118 . Typically, cleaning gases from a cleaning source (not shown) are also introduced through the mixing block  134  to the process volume  112 . A perforated blocker plate  136  is disposed between the showerhead  118  and mixing block  134  to enhance the uniform distribution of gases passing through the showerhead  118  and into the chamber  102 . The blocker plate  136  is typically fabricated from aluminum. 
     An at least partially coated support assembly  138  is disposed beneath the showerhead  118 . The support assembly  138  includes a shaft  142  coupled thereto and supports a substrate  140  during processing. The support assembly is typically accessed by the substrate  140  through a port (not shown) in the walls  106 . A shaft  142  is coupled between the support assembly  138  and a lift mechanism  144 . The lift mechanism  144  moves the support assembly  138  between an elevated position as shown and a lowered position. A bellows  146  disposed between the support assembly  138  or shaft  142  and the chamber bottom  108  provides a vacuum seal between the process volume  112  and the atmosphere outside the chamber  102  while facilitating movement of the support assembly  138 . Lift pins and associated mechanisms have been omitted for clarity. 
     In operation, the semiconductor substrate  140  is secured to the support assembly  138  by providing a vacuum therebetween. The temperature of the substrate is elevated to a pre-determined process temperature by regulating thermal transfer to the support assembly by a heating element described below. During the deposition process, the substrate is heated to a steady temperature, typically between 300° C. and 550° C. 
     Gaseous components, which in one embodiment may include silane and tungsten hexafluoride, are supplied from a gas panel to the process chamber through the mixing block  134  and showerhead  118  to form a gaseous mixture. The gaseous mixture reacts to form a layer of tungsten on the substrate  140 . To prevent deposition at the substrate&#39;s edge and possible adherence of the substrate  140  to the support assembly  138 , purge gases flow from the support assembly  138  around the perimeter of the substrate  140 . 
     FIG. 2 depicts the support assembly  138  in cross-section. The support assembly  138  is generally comprised of aluminum. A heating element  234  is typically embedded or coupled to the support assembly  138 . The heating element  234  may be any number of devices or component that facilitates heat transfer with the support assembly  138 , for example, thermoelectric devices, resistive heaters and conduits for flowing heat transfer fluid, among others. 
     In the embodiment depicted in FIG. 2, the support assembly  138  includes an upper portion  212  and a lower portion  214  having a heating element  234  in the form of an resistive element  210  disposed therebetween. The upper and lower portions  212 ,  214  are coupled by clamping, fastening, welding, brazing and adhering, among other methods. The resistive element  210  is typically fabricated from a conductive material. A power source  232  is coupled to the resistive element  210 . A thermocouple  250  is disposed in the support assembly  138  and is coupled to a controller  252 . The controller  252 , in response to information provided by the thermocouple  250 , controls the power applied to the resistive element  210  from the power source  232  to controllably heat the support assembly  138  and substrate seated thereon to a predetermined temperature. 
     As depicted in FIGS. 2 and 3, a vacuum passage  222  is disposed through the support assembly  138 , coupling a support surface  216  that supports the substrate  140  to a vacuum source  230 . The support surface  216  may include one or more channels  218  disposed therein and coupled to the vacuum passage  222  to uniformly distribute the vacuum applied between the support assembly  138  and the substrate  140 . 
     Returning to FIG. 2, a purge passage  224  is disposed through the support assembly  138 . The purge passage  224  is generally disposed between a lower surface  226  of the lower portion  214  and a side  236  of the support assembly  138 . A purge ring  204  is coupled to the support assembly  138  and defines an annular plenum  238  therebetween. The purge ring  204  is typically fabricated from a material similar or identical to the support assembly  138 , but may alternatively be fabricated from other materials. Purge gas flowing from the purge passage  224  is uniformly distributed in the plenum  238  around the side  236  of the support assembly  138 . One or more purge channels fluidly couple the plenum  238  to the support surface  216  at the circumference of the substrate  140 . In the embodiment depicted in FIG. 2, an annular purge channel  208  is formed between the purge ring  204  and support assembly  138 . Typically, a restrictor  240  is disposed in the flow path between the plenum  238  and purge channel  208  to enhance uniform distribution of gas within the plenum  238 . The purge channel  208  provides purge gas uniformly around the substrate  140  and prevents edge deposition that may adhere the substrate to the support surface  216 . 
     A plurality of alignment pins  206  are typically coupled to the support surface  216  and/or purge ring  204 . The alignment pins  206  may alternatively be an integral part of the purge ring  204 . The alignment pins  206  generally have a sloped face  242  that centers the substrate  140  on the support assembly  138 . 
     A protective coating  220  is typically disposed on at least the upper surface  216  of the support assembly  138 . The coating  220  is typically applied to the upper surface  216  before the purge ring  204  is attached and may additionally cover the side  336 , lower surface  226  and other portions of the support assembly  138  exposed prior to final assembly (i.e., portions of the purge channel  208 , restrictor  240  and plenum  238 ). The coating  220  may additionally be applied to the purge ring  204  and/or alignment pins  206 , either individually, as an assembly. Optionally, the coating  220  may be applied to other aluminum surfaces within the chamber  102 . For examples chamber itself, the showerheads (including gas distribution plates and faceplates), blocker plate among others. 
     Generally, the coating  220  typically comprises a layer of aluminum fluoride (AIF 3 ), magnesium fluoride (MgF 2 ) or other material that prevents penetration of fluoride and/or fluoride containing compounds therethrough. The coating thickness is sufficient to prevent such penetration and is typically between about 12 to 25 μm for AIF 3  and MgF 2  coatings. The coating  220  comprised of AIF 3  generally has a grain structure comprising less than about 6 percent in the beta phase. In one embodiment, the coating has a grain structure comprising less than about 10 percent in the beta phase. The coating typically has an alpha phase grain structure of greater than about 90 percent. The low percentage of grain structure in the beta phase improves adhesion of the coating to the support assembly  138  thereby substantially reducing flaking, peeling and particulate generation associated with conventional coatings having a higher percentage of beta phase grain orientation. 
     The coating  220  may be applied through a number of thermal methods wherein AIF 3  or other coating material is heated to about a semi-liquid, semi-solid state. For example, FIG. 4 depicts one embodiment of a method  400  for applying an AIF 3  coating to a substrate support having an aluminum surface. The method  400  begins at step  402  by heating aluminum fluoride to about a semi-liquid, semi-solid state. Then, at step  404 , the heated aluminum fluoride is applied to the aluminum surface of the support assembly  138 . The applied aluminum fluoride generally forms a layer of material that has less than about 6 percent of the grain structure in the beta phase. In another embodiment, the grain structure of the applied aluminum fluoride is less than about 10 percent in the beta phase. The applied aluminum fluoride having less than about 10 percent of its grain structure in the beta phase has shown good adhesion to aluminum while aluminum fluoride having less than about 8 percent of its grain structure in the beta phase has shown excellent adhesion to aluminum and resistance to cracking and peeling, particularly when utilized in processing equipment operated in a temperature range of between about 425 to about 480 degrees Celsius. Moreover, the resulting surface finish of the coating applied by this process is generally less than or equal to about 24 RA, which minimizes scratching or particular generation of the substrate when seated thereon during processing. Optionally, a grinding or polishing step may be employed to improve the surface finish of the coating  220 . Generally, if a grinding or polishing step is employed, the thickness of the coating  220  should not be reduced to less than about 12 μm thick. 
     The heating step  402  may be accomplished by exposing AIF 3  in powder form to a plasma formed from an inert gas. The plasma may be formed in a chamber where the applying step  404  occurs or may be remotely generated. Typically, argon, neon and/or helium may be utilized to form the plasma. In one embodiment, the temperature of the plasma is about 1450 to about 1600 degrees Celsius. 
     The grain size of the AIF 3  powder used in the plasma heated deposition process is typically in the range of about +100 to −325 mesh. In one embodiment, the AIF 3  powder generally has a grain orientation of at least about 90 percent in the alpha phase. Step  404  of applying the heated AIF 3  to the support assembly  138  is generally accomplished by spraying the heated AIF 3  onto the support surface  216  that is typically at room temperature. The sprayed AIF 3  reaches the support surface  216  in a semi-solid, semi-liquid state. The support assembly  138  having the coating  220  disposed thereon is then cooled at room temperature. 
     FIG. 5 depicts another embodiment of a method for fabricating a substrate support. The method  500  generally begins at step  502  by forming a plasma from an inert gas. At step  504 , AIF 3  is heated with the plasma. At step  506 , the heated AIF 3  is sprayed on the support surface  216  of the support assembly  138 . In one embodiment, AIF 3  is sprayed through the plasma onto the support surface  216 . 
     Although two examples have been illustrated for heating AIF 3  to a semi-liquid, semi-solid state before applying the AIF 3  to the support assembly  138 , other methods of heating AIF 3 to a semi-liquid, semi-solid state before or after application to the substrate support  138  may exist or be developed that produce the coating  220  having a grain orientation of less than about 10 percent in the beta phase and accordingly are contemplated within the scope of the invention. Additionally, the methods  400  and  500  may be adapted to apply MgF 2  or other material that prevents penetration of fluoride and/or fluoride containing compounds therethrough. 
     FIG. 6 depicts another support assembly  600  having a protective coating  602  disposed at least on a support surface  604  of the support assembly  600 . The support assembly  600  is generally fabricated from aluminum and has a heater element  606  embedded therein. In the embodiment depicted in FIG. 6, the heater element  606  is a conduit  608  disposed in a groove  610  formed in a lower surface  612  of the support assembly  600 . The groove  610  has a plug  614  coupled thereto that encloses the conduit  608  in the groove  610 . 
     The conduit  608  is coupled to a heat transfer fluid source  616 . The heat transfer fluid source  616  flows heat transfer fluid through the conduit  608  to thermally regulate the substrate  140  seated on the support surface  604 . 
     A vacuum passage  618  is disposed through the support assembly  600  similar to the passage  222  described above with reference to FIG. 2. A vacuum source  634  is coupled to the vacuum passage  618  and allows for a vacuum to be established between the substrate and the support surface  604  to retain the substrate. The support surface  614  may additionally include channels  632  to distribute the vacuum uniformly under the substrate. 
     A purge ring  620  circumscribes the support surface  604  and forms a purge gas channel  622  with the support assembly  600 . The purge gas channel  622  is coupled to a purge gas source  624  by a purge gas passage  626  formed through the support assembly  600 . The purge ring  620  is coupled to the support assembly  600  by a clamp  628  and pin  630 . Use of a clamp and pin to secure a purge ring to a support assembly is described in greater detail in U.S. Pat. No. 6,223,447, issued May 1, 2001, which is hereby incorporated by reference in its entirety. 
     The coating  602  is generally disposed on at least the support surface  604  but may be additionally disposed on other portions of the support assembly  600 , purge ring  620  and/or clamp  628 . The coating  602  is generally identical to the coating  220  described above with reference to FIGS. 2,  4  and  5 . The coating is more capable of resisting cracking, flaking and the like when exposed to aggressive materials, such as fluorine, while simultaneously protecting the underlying material on which it rests from attack from the aggressive environment. Thus, the coating enhances the service life of coated surfaces while preventing contamination of substrates during processing. 
     The coating  602  applied by the method described above has demonstrated resistance to degradation when exposed to harsh environments, for example environments containing NF 3 . For example, a cleaning cycle in a WxZ™ metal chemical vapor deposition (MCVD) system generally exposes the coating  602  to NF 3  for approximately 40 second per cycle. After by subjecting the coating  602  to  360  cleaning cycles, the coating  602  illustrated no signs of deterioration, cracking, flaking or other detrimental condition. 
     The coating  602  has additionally demonstrated stability under thermal shock conditions. For example, the coating  602  can be rapidly heated to about 475 degrees Celsius. After holding this temperature for about 1.5 hours and allowed to cool at room temperature, no peeling, delamination, cracks or other detrimental condition was evident when examined. 
     A heater or other chamber component coated as described above is advantageous over a component having conventionally applied AIF 3  protective layer. For example, thermal application (e.g., seasoning) of an aluminum heater (substrate supports) costs approximately 10 times as much as applying an AIF 3  coating as described above. Moreover, testing has demonstrated that a heater coated as described above has at least comparable longevity as compared to seasoned heaters, lasting upwards of 10,000 deposition cycles, and accordingly may readily replace existing heaters with substantially no impact on substrate throughput. 
     Although teachings of the present invention that have been shown and described in detail herein, those skilled in the art can readily devise other varied embodiments that still incorporate the teachings and do not depart from the scope and spirit of the invention.