Patent Publication Number: US-2011076400-A1

Title: Nanocrystalline diamond-structured carbon coating of silicon carbide

Description:
This application claims the benefit of and priority to Provisional Application Ser. No. 61/247,495, filed Sep. 30, 2009 which is hereby incorporated by reference. 
    
    
     BACKGROUND 
     1. Field 
     Embodiments of the present invention relate to forming a nanocrystalline diamond-structured carbon layer on a silicon carbide layer. 
     2. Discussion of Related Art 
     Chemical vapor deposition (CVD) reactor parts made of silicon carbide can deteriorate over time when exposed to chlorinated environments at high temperature. One example of this is during an insitu clean of a CVD reactor, which typically uses HCl or Cl 2  at elevated temperatures to clean the CVD reactor. Deterioration of CVD reactor parts can occur in a variety of processing chambers including CVD reactor chambers, metal organic chemical vapor deposition (MOCVD) reactor chambers, and hydride vapor phase epitaxy (HVPE) reactor chambers. Hence, a chemically inert and mechanically stable protective layer on silicon carbide is desirable to prevent deterioration of silicon carbide CVD reactor parts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a carbon-silicon carbide structure in accordance with an embodiment of the present invention. 
         FIG. 2  is an illustration of process steps for forming a carbon layer on a silicon carbide layer in accordance with an embodiment of the present invention. 
         FIG. 3  is a FIB XSEM/EDX showing a carbon-silicon carbide structure formed in accordance with an embodiment of the present invention. 
         FIG. 4A  is a chart of minimum/maximum thickness of a carbide derived carbon (CDC) film formed in accordance with an embodiment of the present invention 
         FIG. 4B  is a high resolution Auger Electron Spectroscopy (AES) study of a carbon layer formed in accordance with an embodiment of the present invention. 
         FIG. 5  is an isometric view illustrating a processing system according to an embodiment of the invention. 
         FIG. 6  is a plan view of the processing system illustrated in  FIG. 7 . 
         FIG. 7  is an isometric view illustrating a load station and loadlock chamber according to an embodiment of the invention. 
         FIG. 8  is a schematic view of a loadlock chamber according to an embodiment of the invention. 
         FIG. 9  is an isometric view of a carrier plate according to an embodiment of the invention. 
         FIG. 10  is a schematic view of a batch loadlock chamber according to an embodiment of the invention. 
         FIG. 11  is an isometric view of a work platform according to an embodiment of the invention. 
         FIG. 12  is a plan view of a transfer chamber according to an embodiment of the invention. 
         FIG. 13  is a schematic cross-sectional view of a HVPE chamber according to an embodiment of the invention. 
         FIG. 14  is a schematic cross-sectional view of an MOCVD chamber according to an embodiment of the invention. 
         FIG. 15  is a schematic view illustrating another embodiment of a processing system for fabricating compound nitride semiconductor devices. 
         FIG. 16  is a schematic view illustrating yet another embodiment of a processing system for fabricating compound nitride semiconductor devices. 
     
    
    
     SUMMARY 
     A method of forming a nanocrystalline diamond structure-carbon layer is described. According to embodiments of the present invention, a silicon carbide layer is exposed to a chlorine containing gas for an exposure time period sufficient to allow the formation of a nanocrystalline diamond-structure carbon layer. In an embodiment of the present invention, a silicon carbide layer is exposed to a chlorine containing gas, such as but not limited to Cl 2  or HCl while the silicon carbide layer is heated to a temperature greater than 600° C. and generally between 600-1000° C. 
     DETAILED DESCRIPTION 
     Embodiments of the present invention relate to a method of forming a nanocrystalline diamond-structured carbon layer. In the present description, numerous specific details have been set forth in order to provide a thorough understanding of the present invention. In other instances, well known semiconductor processes and equipment have not been described in specific detail in order to not unnecessarily obscure the present invention. 
     Embodiments of the present invention describe a method of forming a nanocrystalline diamond-structured carbon layer on a silicon carbide layer. In an embodiment of the present invention, a silicon carbide layer is provided in a reaction chamber and exposed to a chlorine containing gas for an exposure time period at a temperature sufficiently high to allow for the formation of a nanocrystalline diamond-structured carbon layer on the silicon carbide (SiC) layer. In an embodiment of the present invention, the limited reaction kinetics of the chlorine (Cl) and silicon carbide (SiC) reaction allows for the controlled formation of the nanocrystalline diamond-structured carbon layer on the silicon carbide (SiC) layer. The nanocrystalline diamond-structured carbon layer can be formed to a desired thickness by controlling the exposure time period and temperature of the silicon carbide layer to the chlorine containing gas in accordance with an embodiment of the present invention. 
       FIG. 1  illustrates a carbon-silicon carbide structure  100  in accordance with an embodiment of the present invention. In an embodiment of the present invention, the carbon-silicon carbide structure  100  may comprise a silicon carbide layer  102  with a carbon layer  104  formed on silicon carbide layer  102 . In a specific embodiment of the present invention, the silicon carbide layer  102  is a single crystalline silicon carbide layer. In other embodiments the silicon carbide layer may be a pressed silicon carbide layer or a polycrystalline silicon carbide layer. In embodiments of the present invention, the silicon carbide layer  102  can be a silicon carbide substrate or wafer, a silicon carbide layer on a different type of substrate or wafer, or can be a CVD reactor part. In an embodiment of the present invention, a surface portion of silicon carbide layer  102  is transformed into carbon layer  104  thereby forming a carbide derived carbon (CDC) layer  104 . In a specific embodiment of the present invention, the carbon layer  104  is a nanocrystalline diamond-structured carbon layer or a “diamond like” carbon layer  104 . 
       FIG. 2  illustrates process steps  200  of forming carbon layer  104  on silicon carbide layer  102  in accordance with an embodiment of the present invention. Embodiments of process steps  200  may comprise providing silicon carbide layer  102  in a reaction chamber, as set forth in block  202 ; reducing the pressure inside the reaction chamber, as set forth in block  204 ; heating the silicon carbide layer  102 , as set forth in block  206 ; flowing a chlorine containing gas and an inert gas into the reaction chamber, as set forth in block  208 ; and exposing the silicon carbide layer  102  to a chlorine containing gas for an exposure time period, as set forth in block  210 . 
     In an embodiment of the present invention, block  204  may comprise reducing the reaction chamber pressure to a pressure sufficiently low to facilitate the formation of carbon layer  104  on silicon carbide layer  102 . In a specific embodiment of the present invention, the reaction chamber pressure can be between 5 torr and 760 torr. In an embodiment of the present invention, block  206  may comprise heating the silicon carbide layer  102  to a temperature sufficiently high to allow the formation of carbon layer  104  on the silicon carbide layer  102 . In an embodiment of the present invention silicon carbide layer  102  is heated to a temperature greater than 600° C. In a specific embodiment of the present invention the silicon carbide layer  104  is heated to a temperature between 600° C. and 1000° C. In an embodiment of the present invention, the temperature of the silicon carbide layer  102  is constant throughout process steps  200 . 
     In an embodiment of the present invention, as set forth in block  208  the silicon carbide layer  102  is exposed to a chlorinated ambient by flowing a chlorine containing gas and an inert gas into the reaction chamber. The chlorine containing gas can be any suitable chlorine containing gas, such as but not limited to gaseous HCl or Cl 2 . The inert gas can be any suitable inert gas, such as but not limited to N 2 , Ar or He. In embodiments of the present invention, the chlorine containing gas and the inert gas can be introduced into the reaction chamber at a flow rate between 1.0 and 7.0 standard liter per minute (SLM). In a specific embodiment of the present invention, the silicon carbide layer is exposed to Cl 2  at a flow rate of 1 SLM and N 2  at a flow rate of 6 SLM. 
     In one embodiment, the chlorine containing gas reacts with an exposed surface portion of silicon carbide layer  102 . However, the chlorine containing gas reacts more favorably with the silicon atoms than the carbon atoms of the silicon carbide layer  102 . As a result, chlorine atoms from the chlorine containing gas form silicon-chlorine bonds with silicon atoms of the silicon carbide layer  102  to form gaseous silicon tetrachloride (SiCl 4 ). Meanwhile, carbon atoms of the silicon carbide layer  102  remain unreacted. In an example using gaseous Cl 2 , one molar equivalent of silicon carbide layer  102  (SiC) reacts with two molar equivalents of gaseous chlorine (Cl 2 ) to provide one molar equivalent of gaseous silicon tetrachloride (SiCl 4 ), while one molar equivalent of carbon (C) remains unreacted. The balanced reaction equation is: 
       SiC+2Cl 2 ( g )=SiCl 4 ( g )+C 
     The gaseous silicon tetrachloride (SiCl 4 ) is removed from the reaction chamber while the carbon remains to provide carbon layer  104  on the silicon carbide layer  102 , in accordance with an embodiment of the present invention. Thus, the exposed surface portion of silicon carbide layer  102  is transformed into carbon layer  104 . In one embodiment, carbon layer  104  is a diamond layer and has a three-dimensional network of ordered carbon atoms, as opposed to a two-dimensional network of carbon atoms as is found in graphite. In a specific embodiment, carbon layer  104  is a nano-structured diamond layer. 
     The chlorine containing gas may react more favorably with the silicon atoms than the carbon atoms of silicon carbide layer  102  for kinetic reasons. For example, the formation of gaseous silicon tetrachloride (SiCl 4 ) is much more favorable than the formation of gaseous carbon tetrachloride (CCl 4 ). In other words, chlorine reacts faster with silicon than carbon because less energy is required to activate the reaction. Furthermore, the kinetic energetics of silicon-chlorine bond formation is more rapid than for carbon-chlorine bond formation. In one embodiment, kinetic factors allow the chlorine containing gas to selectively react with the silicon atoms, instead of the carbon atoms, present at the surface of silicon carbide layer  102 . 
     In an embodiment of the present invention, block  210  may comprise exposing the silicon carbide layer  102  to the chlorine containing gas for an exposure time period. The reaction between the chlorine containing gas and the silicon carbide layer  102  is a kinetically limited reaction. The limited reaction kinetics of the chlorine and silicon carbide reaction allows for controlled transformation of the silicon carbide into a carbon layer  104  of a desired thickness in accordance with an embodiment of the present invention. In an embodiment of the present invention, carbon layer  104  can be formed, in the manner described above, to a desired thickness by controlling the exposure time period of the silicon carbide layer  102  to the chlorine containing gas. In an embodiment of the present invention, the silicon carbide layer  102  is exposed to a chlorinated ambient for between one minute to 12 hours to form a carbon layer having a thickness between 3-15 μm. In an embodiment of the present invention, the transformation of silicon carbide to carbon begins to saturates after an exposure period of about 3.0 hours. 
       FIG. 3  illustrates a FIB XSEM/EDX showing a carbon-silicon carbide structure  300  formed in accordance with an embodiment of the present invention. Carbon-silicon carbide structure  300  includes a silicon carbide layer  302  and a carbon layer  304 . In a specific embodiment of the present invention, a carbide derived carbon (CDC) layer  304  was produced by C12 treatment of a Bridgestone Silicon Carbide (SiC) film  302  (Bridgestone SiC films are currently used as susceptors and carrier materials in Applied Materials reactors, such as chemical vapor deposition (CVD) reactors). Specifically the carbide derived carbon (CDD) layer  304  was formed by reducing the chamber pressure to 450 torr, heating the silicon carbide layer  302  to a temperature of 950° C., introducing Cl 2  into the reaction chamber at a flow rate of 1 SLM, introducing N 2  into the chamber at a flow rate of 7 SLM, and exposing the silicon carbide layer  302  to the chlorine containing gas for an exposure time period of 12 hours. Carbon layer  304 , formed on silicon carbide layer  302 , is nanocrystalline diamond-structured carbon layer in accordance with an embodiment of the present invention. 
       FIG. 4A  is an illustration of the minimum and maximum thickness plots of the resulting carbon layer  304  when silicon carbide layer  302  is exposed to chlorine ambient under the condition set forth above for 1, 3, 6 and 12 hours. In embodiment of the present invention, carbon layer  304  can be formed to a thickness of between 3.0 microns and 15.0 microns with an exposure time period between 1.0 hours and 12.0 hours. In a specific embodiment of the present an exposure time period of 1.0 hours formed a carbon layer with a minimum thickness of about 3.0 microns and a maximum thickness of about 3.0 microns. In other embodiments of the present invention, an exposure time period of 3.0 hours formed a carbon layer with a minimum thickness of 10.0 microns and a maximum thickness of 15.0 microns, an exposure time period of 6.0 hours formed a carbon layer with a minimum thickness of 14.0 microns and a maximum thickness of 17.0 microns, and an exposure time period of 12.0 hours formed a carbon layer with a minimum thickness of 13.5 microns and a maximum thickness of 15.0 microns. 
       FIG. 4B  illustrates a high resolution Auger Electro Spectroscopy (AES) study  400  of the carbon layer  304 . Diamond-like carbon reference line  402  depicts the AES spectra of a carbon layer having a diamond-like structure. Graphitic carbon reference line  404  depicts the AES spectra of a carbon layer having a graphitic structure. Carbon layer spectra line  406  depicts the AES spectra of carbon layer  304  formed in the manner described above with an exposure time of one hour. Diamond-like carbon reference line  402  and graphitic carbon reference line  404  are overlaid on carbon layer spectra line  406  to illustrate the type of carbon structure carbon layer  304  comprises. Graphitic carbon reference line  404  has a notable double peak  408  at higher kinetic energy, in the AES study, that is characteristic of graphitic structures. Absence of the double peak  408  in the carbon layer spectra line  406  and the similarity of the carbon layer spectra line  406  to the diamond-like reference line  402  indicate that carbon layer  304  is a nanocrystalline diamond-structured carbon layer that was formed in accordance with an embodiment of the present invention. 
     Thus, the process method  200  described above transforms the exposed surface of a silicon carbide layer into a nanocrystalline diamond-structured carbon layer in accordance with an embodiment of the present invention. A nanocrystalline diamond-structured carbon layer is mechanically stable and chemically inert. Such characteristics make a nanocrystalline diamond-structured carbon layer useful in a wide variety of industrial and commercial applications due to the high corrosion resistance of such a layer. Specifically, these characteristics are desirable for CVD or HVPE reactor parts which are exposed to chlorinated environments at high temperature. Silicon carbide coated with a nanocrystalline diamond-structured layer can be used in any application where corrosion resistance is desirable. Additionally, in embodiments of the present application, the nanocrystalline diamond-structured layer may be harvested from the silicon carbide layer and used in a wide variety of industrial and commercial applications in addition to those mentioned above. 
     The process of forming a nanocrystalline diamond structure carbon layer can be carried out in any chamber which as chlorine (Cl 2 ) gas, such as but not limited to, a chemical vapor deposition chamber (CVD), a metal organic chemical vapor deposition chamber (MOCVD) and a hydride vapor phase epitaxial (HVPE) chamber. In an embodiment of the present invention, the nanocrystalline diamond structure carbon layer can be formed in a process system  500 , such as illustrated in  FIG. 5 , which contains an HVPE chamber and a MOCVD chamber, typically used to form light emitting diodes. 
       FIG. 5  is an isometric view of one embodiment of a processing system  500  that illustrates a number of aspects of the present invention that may be advantageously used.  FIG. 6  illustrates a plan view of one embodiment of a processing system  500  illustrated in  FIG. 5 . With reference to  FIG. 5  and  FIG. 6 , the processing system  500  comprises a transfer chamber  506  housing a substrate handler, a plurality of processing chambers coupled with the transfer chamber, such as a MOCVD chamber  502  and a HVPE chamber  504 , a loadlock chamber  508  coupled with the transfer chamber  506 , a batch loadlock chamber  509 , for storing substrates, coupled with the transfer chamber  506 , and a load station  510 , for loading substrates, coupled with the loadlock chamber  508 . The transfer chamber  506  comprises a robot assembly  530  operable to pick up and transfer substrates between the loadlock chamber  508 , the batch loadlock chamber  509 , the MOCVD chamber  502  and the HVPE chamber  504 . The movement of the robot assembly  530  may be controlled by a motor drive system (not shown), which may include a servo or stepper motor. 
     Each processing chamber comprises a chamber body (such as element  512  for the MOCVD chamber  502  and element  514  for the HVPE chamber  504 ) forming a processing region where a substrate is placed to undergo processing, a chemical delivery module (such as element  516  for the MOCVD chamber  502  and element  518  for the HVPE chamber  504 ) from which gas precursors are delivered to the chamber body, and an electrical module (such as element  520  for the MOCVD chamber  502  and element  522  for the HVPE chamber  504 ) that includes the electrical system for each processing chamber of the processing system  500 . The MOCVD chamber  502  is adapted to perform CVD processes in which metalorganic elements react with metal hydride elements to form thin layers of compound nitride semiconductor materials. The HVPE chamber  504  is adapted to perform HVPE processes in which gaseous metal halides are used to epitaxially grow thick layers of compound nitride semiconductor materials on heated substrates. The nanocrystalline diamond structure carbon coating of the present invention may be formed on silicon carbide containing substrates placed in MOCVD chamber  502  and/or HVPE chamber  504  or may be formed on silicon carbide components or parts, such as substrate carriers, of MOCVD chamber  502  and/or HVPE chamber  504 . In alternate embodiments, one or more additional chambers may  570  be coupled with the transfer chamber  506 . These additional chambers may include, for example, anneal chambers, clean chambers for cleaning carrier plates, or substrate removal chambers. The structure of the processing system permits substrate transfers to occur in a defined ambient environment, including under vacuum, in the presence of a selected gas, under defined temperature conditions, and the like. 
       FIG. 7  is an isometric view illustrating a load station  510  and a loadlock chamber  508  according to an embodiment of the invention. The load station  510  is configured as an atmospheric interface to allow an operator to load a plurality of substrates for processing into the confined environment of the loadlock chamber  508 , and unload a plurality of processed substrates from the loadlock chamber  508 . The load station  510  comprises a frame  702 , a rail track  704 , a conveyor tray  706  adapted to slide along the rail track  704  to convey substrates into and out of the loadlock chamber  508  via a slit valve  710 , and a lid  711 . In one embodiment, the conveyor tray  706  may be moved along the rail track  704  manually by the operator. In another embodiment, the conveyor tray  706  may be driven mechanically by a motor. In yet another embodiment, the conveyor tray  706  is moved along the rail track  704  by a pneumatic actuator. 
     Substrates for processing may be grouped in batches and transported on the conveyor tray  706 . For example, each batch of substrates  714  may be transported on a carrier plate  712  that can be placed on the conveyor tray  706 . The lid  711  may be selectively opened and closed over the conveyor tray  706  for safety protection when the conveyor tray  706  is driven in movement. In operation, an operator opens the lid  711  to load the carrier plate  712  containing a batch of substrates on the conveyor tray  706 . A storage shelf  716  may be provided for storing carrier plates containing substrates to be loaded. The lid  711  is closed, and the conveyor tray  706  is moved through the slit valve  710  into the loadlock chamber  508 . The lid  711  may comprise a glass material, such as Plexiglas or a plastic material to facilitate monitoring of operations of the conveyor tray  706 . 
       FIG. 8  is a schematic view of a loadlock chamber  508  according to an embodiment of the invention. The loadlock chamber  508  provides an interface between the atmospheric environment of the load station  510  and the controlled environment of the transfer chamber  506 . Substrates are transferred between the loadlock chamber  508  and the load station  510  via the slit valve  710  and between the loadlock chamber  508  and the transfer chamber  506  via a slit valve  842 . The loadlock chamber  508  comprises a carrier support  844  adapted to support incoming and outgoing carrier plates thereon. In one embodiment, the loadlock chamber  508  may comprise multiple carrier supports that are vertically stacked. To facilitate loading and unloading of a carrier plate, the carrier support  844  may be coupled to a stem  846  vertically movable to adjust the height of the carrier support  844 . The loadlock chamber  508  is coupled to a pressure control system (not shown) which pumps down and vents the loadlock chamber  508  to facilitate passing the substrate between the vacuum environment of the transfer chamber  506  and the substantially ambient (e.g., atmospheric) environment of the load station  510 . In addition, the loadlock chamber  508  may also comprise features for temperature control, such as a degas module  848  to heat substrates and remove moisture, or a cooling station (not shown) for cooling substrates during transfer. Once a carrier plate loaded with substrates has been conditioned in the loadlock chamber  508 , the carrier plate may be transferred into the MOCVD chamber  502  or the HVPE chamber  504  for processing, or to the batch loadlock chamber  509  where multiple carrier plates are stored in standby for processing. 
     During operation, a carrier plate  712  containing a batch of substrates is loaded on the conveyor tray  706  in the load station  510 . The conveyor tray  706  is then moved through the slit valve  710  into the loadlock chamber  508 , placing the carrier plate  712  onto the carrier support  844  inside the loadlock chamber  508 , and the conveyor tray returns to the load station  510 . While the carrier plate  712  is inside the loadlock chamber  508 , the loadlock chamber  508  is pumped and purged with an inert gas, such as nitrogen, in order to remove any remaining oxygen, water vapor, and other types of contaminants. After the batch of substrates have been conditioned in the loadlock chamber, the robot assembly  530  may transfer the carrier plate  712  to either the MOCVD chamber  502  or, the HVPE chamber  504  to undergo deposition processes. In alternate embodiments, the carrier plate  712  may be transferred and stored in the batch loadlock chamber  509  on standby for processing in either the MOCVD chamber  502  or the HVPE chamber  504 . After processing of the batch of substrates is complete, the carrier plate  712  may be transferred to the loadlock chamber  508 , and then retrieved by the conveyor tray  706  and returned to the load station  510 . 
       FIG. 9  is an isometric view of a carrier plate according to an embodiment of the invention. In one embodiment, the carrier plate  712  may include one or more circular recesses  910  within which individual substrates may be disposed during processing. The size of each recess  910  may be changed according to the size of the substrate to accommodate therein. In one embodiment, the carrier plate  712  may carry six or more substrates. In another embodiment, the carrier plate  712  carries eight substrates. In yet another embodiment, the carrier plate  712  carries 18 substrates. It is to be understood that more or less substrates may be carried on the carrier plate  712 . Typical substrates may include sapphire, silicon carbide (SiC), silicon, or gallium nitride (GaN). It is to be understood that other types of substrates, such as glass substrates, may be processed. Substrate size may range from 50 mm-200 mm in diameter or larger. In one embodiment, each recess  910  may be sized to receive a circular substrate having a diameter between about 2 inches and about 6 inches. The diameter of the carrier plate  712  may range from 200 mm-750 mm, for example, about 300 mm. The carrier plate  712  may be formed from a variety of materials, including SiC, SiC-coated graphite, or other materials resistant to the processing environment. Substrates of other sizes may also be processed within the processing system  500  according to the processes described herein. 
       FIG. 10  is a schematic view of the batch loadlock chamber  509  according to an embodiment of the invention. The batch loadlock chamber  509  comprises a body  1005  and a lid  1034  and bottom  1016  disposed on the body  1005  and defining a cavity  1007  for storing a plurality of substrates placed on the carrier plates  712  therein. In one aspect, the body  1005  is formed of process resistant materials such as aluminum, steel, nickel, and the like, adapted to withstand process temperatures and is generally free of contaminates such as copper. The body  1005  may comprise a gas inlet  1060  extending into the cavity  1007  for connecting the batch loadlock chamber  509  to a process gas supply (not shown) for delivery of processing gases therethrough. In another aspect, a vacuum pump  1090  may be coupled to the cavity  1007  through a vacuum port  1092  to maintain a vacuum within the cavity  1007 . 
     A storage cassette  1010  is moveably disposed within the cavity  1007  and is coupled with an upper end of a movable member  1030 . The moveable member  1030  is comprised of process resistant materials such as aluminum, steel, nickel, and the like, adapted to withstand process temperatures and generally free of contaminates such as copper. The movable member  1030  enters the cavity  1007  through the bottom  1016 . The movable member  1030  is slidably and sealably disposed through the bottom  1016  and is raised and lowered by the platform  1087 . The platform  1087  supports a lower end of the movable member  1030  such that the movable member  1030  is vertically raised or lowered in conjunction with the raising or lowering of the platform  1087 . The movable member  1030  vertically raises and lowers the storage cassette  1010  within the cavity  1007  to move the substrates carrier plates  712  across a substrate transfer plane  1032  extending through a window  1035 . The substrate transfer plane  1032  is defined by the path along which substrates are moved into and out of the storage cassette  1010  by the robot assembly  530 . 
     The storage cassette  1010  comprises a plurality of storage shelves  1036  supported by a frame  1025 . Although in one aspect,  FIG. 10  illustrates twelve storage shelves  1036  within storage cassette  1010 , it is contemplated that any number of shelves may be used. Each storage shelf  1036  comprises a substrate support  1040  connected by brackets  1017  to the frame  1025 . The brackets  1017  connect the edges of the substrate support  1040  to the frame  1025  and may be attached to both the frame  1025  and substrate support  1040  using adhesives such as pressure sensitive adhesives, ceramic bonding, glue, and the like, or fasteners such as screws, bolts, clips, and the like that are process resistant and are free of contaminates such as copper. The frame  1025  and brackets  1017  are comprised of process resistant materials such as ceramics, aluminum, steel, nickel, and the like that are process resistant and are generally free of contaminates such as copper. While the frame  1025  and brackets  1017  may be separate items, it is contemplated that the brackets  1017  may be integral to the frame  1025  to form support members for the substrate supports  1040 . 
     The storage shelves  1036  are spaced vertically apart and parallel within the storage cassette  1010  to define a plurality of storage spaces  1022 . Each substrate storage space  1022  is adapted to store at least one carrier plate  712  therein supported on a plurality of support pins  1042 . The storage shelves  1036  above and below each carrier plate  712  establish the upper and lower boundary of the storage space  1022 . 
     In another embodiment, substrate support  1040  is not present and the carrier plates  712  rest on brackets  1017 . 
       FIG. 11  is an isometric view of a work platform  1100  according to one embodiment of the invention. In one embodiment, the processing system  500  further comprises a work platform  1100  enclosing the load station  510 . The work platform  1100  provides a particle free environment during loading and unloading of substrates into the load station  510 . The work platform  1100  comprises a top portion  1102  supported by four posts  1104 . A curtain  1110  separates the environment inside the work platform  1100  from the surrounding environment. In one embodiment, the curtain  1110  comprises a vinyl material. In one embodiment the work platform comprises an air filter, such as a High Efficiency Particulate Air Filter (“HEPA”) filter for filtering airborne particles from the ambient inside the work platform. In one embodiment, air pressure within the enclosed work platform  1100  is maintained at a slightly higher pressure than the atmosphere outside of the work platform  1100  thus causing air to flow out of the work platform  1100  rather than into the work platform  1100 . 
       FIG. 12  is a plan view of a robot assembly  530  shown in the context of the transfer chamber  506 . The internal region (e.g., transfer region  1240 ) of the transfer chamber  506  is typically maintained at a vacuum condition and provides an intermediate region in which to shuttle substrates from one chamber to another and/or to the loadlock chamber  508  and other chambers in communication with the cluster tool. The vacuum condition is typically achieved by use of one or more vacuum pumps (not shown), such as a conventional rough pump, Roots Blower, conventional turbo-pump, conventional cryo-pump, or combination thereof. Alternately, the internal region of the transfer chamber  506  may be an inert environment that is maintained at or near atmospheric pressure by continually delivering an inert gas to the internal region. Three such platforms are the Centura, the Endura and the Producer system all available from Applied Materials, Inc., of Santa Clara, Calif. The details of one such staged-vacuum substrate processing system are disclosed in U.S. Pat. No. 5,186,718, entitled “Staged-Vacuum Substrate Processing System and Method,” Tepman et al., issued on Feb. 16, 1993, which is incorporated herein by reference. The exact arrangement and combination of chambers may be altered for purposes of performing specific steps of a fabrication process. 
     The robot assembly  530  is centrally located within the transfer chamber  506  such that substrates can be transferred into and out of adjacent processing chambers, the loadlock chamber  508 , and the batch loadlock chamber  509 , and other chambers through slit valves  842 ,  1212 ,  1214 ,  1216 ,  1218 , and  1220  respectively. The valves enable communication between the processing chambers, the loadlock chamber  508 , the batch loadlock chamber  509 , and the transfer chamber  506  while also providing vacuum isolation of the environments within each of the chambers to enable a staged vacuum within the system. The robot assembly  530  may comprise a frog-leg mechanism. In certain embodiments, the robot assembly  530  may comprise any variety of known mechanical mechanisms for effecting linear extension into and out of the various process chambers. A blade  1210  is coupled with the robot assembly  530 . The blade  1210  is configured to transfer the carrier plate  712  through the processing systems. In one embodiment, the processing system  500  comprises an automatic center finder (not shown). The automatic center finder allows for the precise location of the carrier plate  712  on the robot assembly  530  to be determined and provided to a controller. Knowing the exact center of the carrier plate  712  allows the computer to adjust for the variable position of each carrier plate  712  on the blade and precisely position each carrier plate  712  in the processing chambers. 
       FIG. 13  is a schematic cross-sectional view of a HVPE chamber  504  according to an embodiment of the invention. The HVPE chamber  504  includes the chamber body  514  that encloses a processing volume  1308 . A showerhead assembly  1304  is disposed at one end of the processing volume  1308 , and the carrier plate  712  is disposed at the other end of the processing volume  1308 . The showerhead assembly, as described above, may allow for more uniform deposition across a greater number of substrates or larger substrates than in traditional HVPE chambers, thereby reducing production costs. The showerhead may be coupled with a chemical delivery module  518 . The carrier plate  712  may rotate about its central axis during processing. In one embodiment, the carrier plate  712  may be rotated at about 2 RPM to about 100 RPM. In another embodiment, the carrier plate  712  may be rotated at about 30 RPM. Rotating the carrier plate  712  aids in providing uniform exposure of the processing gases to each substrate. 
     A plurality of lamps  1330   a ,  1330   b  may be disposed below the carrier plate  712 . For many applications, a typical lamp arrangement may comprise banks of lamps above (not shown) and below (as shown) the substrate. One embodiment may incorporate lamps from the sides. In certain embodiments, the lamps may be arranged in concentric circles. For example, the inner array of lamps  1330   b  may include eight lamps, and the outer array of lamps  1330   a  may include twelve lamps. In one embodiment of the invention, the lamps  1330   a ,  1330   b  are each individually powered. In another embodiment, arrays of lamps  1330   a ,  1330   b  may be positioned above or within showerhead assembly  1304 . It is understood that other arrangements and other numbers of lamps are possible. The arrays of lamps  1330   a ,  1330   b  may be selectively powered to heat the inner and outer areas of the carrier plate  712 . In one embodiment, the lamps  1330   a ,  1330   b  are collectively powered as inner and outer arrays in which the top and bottom arrays are either collectively powered or separately powered. In yet another embodiment, separate lamps or heating elements may be positioned over and/or under the source boat  1380 . It is to be understood that the invention is not restricted to the use of arrays of lamps. Any suitable heating source may be utilized to ensure that the proper temperature is adequately applied to the processing chamber, substrates therein, and a metal source. For example, it is contemplated that a rapid thermal processing lamp system may be utilized such as is described in United States Patent Publication No. 2006/0018639, published Jan. 26, 2006, entitled PROCESSING MULTILAYER SEMICONDUCTORS WITH MULTIPLE HEAT SOURCES, which is incorporated by reference in its entirety. 
     In yet another embodiment, the source boat  1380  is remotely located with respect to the chamber body  514 , as described in U.S. Provisional Patent Application Ser. No. 60/978,040, filed Oct. 5, 2007, titled METHOD FOR DEPOSITING GROUP III/V COMPOUNDS, which is incorporated by reference in its entirety. 
     One or more lamps  1330   a ,  1330   b  may be powered to heat the substrates as well as the source boat  1380 . The lamps may heat the substrate to a temperature of about 900° C. to about 1200° C. In another embodiment, the lamps  1330   a ,  1330   b  maintain a metal source within the source boat  1380  at a temperature of about 350° C. to about 900° C. A thermocouple may be used to measure the metal source temperature during processing. The temperature measured by the thermocouple may be fed back to a controller that adjusts the heat provided from the heating lamps  1330   a ,  1330   b  so that the temperature of the metal source may be controlled or adjusted as necessary. 
     Precursor gases  1306  flow from the showerhead assembly  1304  towards the substrate surface. Reaction of the precursor gases  1306  at or near the substrate surface may deposit various metal nitride layers upon the substrate, including GaN, AlN, and InN. Multiple metals may also be utilized for the deposition of “combination films” such as AlGaN and/or InGaN. The processing volume  1308  may be maintained at a pressure of about 760 torr down to about 100 torr. In one embodiment, the processing volume  1308  is maintained at a pressure of about 450 torr to about 760 torr. Exemplary embodiments of the showerhead assembly  1304  and other aspects of the HVPE chamber are described in U.S. patent application Ser. No. 11/767,520, filed Jun. 24, 2007, entitled HVPE TUBE SHOWERHEAD DESIGN, which is herein incorporated by reference in its entirety. Exemplary embodiments of the HVPE chamber  504  are described in U.S. Patent Application Ser. No. 61/172,630, filed Apr. 24, 2009, entitled HVPE CHAMBER HARDWARE, which is herein incorporated by reference in its entirety. Alternatively, Cl 2  gas may be fed into the processing volume under conditions set forth above to form a nanocrystalline diamond-structure carbon coating on a silicon carbide substrate or silicon carbide layer on a substrate contained within volume  1308  or on silicon carbide chamber components or parts within volume  1308 . 
       FIG. 14  is a schematic cross-sectional view of an MOCVD chamber according to an embodiment of the invention. The MOCVD chamber  502  comprises a chamber body  512 , a chemical delivery module  516 , a remote plasma source  1426 , a substrate support  1414 , and a vacuum system  1412 . The chamber  502  includes a chamber body  512  that encloses a processing volume  1408 . A showerhead assembly  1404  is disposed at one end of the processing volume  1408 , and a carrier plate  712  is disposed at the other end of the processing volume  1408 . The carrier plate  712  may be disposed on the substrate support  1414 . In an embodiment of the present invention, Cl 2  gas may be fed into processing volume  1408  under conditions set forth above to form a nanocrystalline diamond structure carbon coating on a silicon carbide substrate or silicon carbide layer on a substrate contained in processing volume  1408  or onto silicon carbide chamber components or parts within volume  1408 . Exemplary showerheads that may be adapted to practice the present invention are described in U.S. patent application Ser. No. 11/873,132, filed Oct. 16, 2007, entitled MULTI-GAS STRAIGHT CHANNEL SHOWERHEAD, U.S. patent application Ser. No. 11/873,141, filed Oct. 16, 2007, entitled MULTI-GAS SPIRAL CHANNEL SHOWERHEAD, and 11/873,170, filed Oct. 16, 2007, entitled MULTI-GAS CONCENTRIC INJECTION SHOWERHEAD, all of which are incorporated by reference in their entireties. 
     A lower dome  1419  is disposed at one end of a lower volume  1410 , and the carrier plate  712  is disposed at the other end of the lower volume  1410 . The carrier plate  712  is shown in process position, but may be moved to a lower position where, for example, the substrates  1440  may be loaded or unloaded. An exhaust ring  1420  may be disposed around the periphery of the carrier plate  712  to help prevent deposition from occurring in the lower volume  1410  and also help direct exhaust gases from the chamber  502  to exhaust ports  1409 . The lower dome  1419  may be made of transparent material, such as high-purity quartz, to allow light to pass through for radiant heating of the substrates  1440 . The radiant heating may be provided by a plurality of inner lamps  1421 A and outer lamps  1421 B disposed below the lower dome  1419  and reflectors  1466  may be used to help control the chamber  502  exposure to the radiant energy provided by inner and outer lamps  1421 A,  1421 B. Additional rings of lamps may also be used for finer temperature control of the substrates  1440 . 
     A purge gas (e.g., nitrogen) may be delivered into the chamber  502  from the showerhead assembly  1404  and/or from inlet ports or tubes (not shown) disposed below the carrier plate  712  and near the bottom of the chamber body  512 . The purge gas enters the lower volume  1410  of the chamber  502  and flows upwards past the carrier plate  712  and exhaust ring  1420  and into multiple exhaust ports  1409  which are disposed around an annular exhaust channel  1405 . An exhaust conduit  1406  connects the annular exhaust channel  1405  to a vacuum system  1412  which includes a vacuum pump (not shown). The chamber  502  pressure may be controlled using a valve system  1407  which controls the rate at which the exhaust gases are drawn from the annular exhaust channel  1405 . Other aspects of the MOCVD chamber are described in U.S. patent application Ser. No. 12/023,520, filed Jan. 31, 2008, (attorney docket no. 011977) entitled CVD APPARATUS, which is herein incorporated by reference in its entirety. 
     Various metrology devices, such as, for example, reflectance monitors, thermocouples, or other temperature devices may also be coupled with the chamber  502 . The metrology devices may be used to measure various film properties, such as thickness, roughness, composition, temperature or other properties. These measurements may be used in an automated real-time feedback control loop to control process conditions such as deposition rate and the corresponding thickness. Other aspects of chamber metrology are described in U.S. Patent Application Ser. No. 61/025,252, filed Jan. 31, 2008, (attorney docket no. 011007) entitled CLOSED LOOP MOCVD DEPOSITION CONTROL, which is herein incorporated by reference in its entirety. 
     The chemical delivery modules  516 ,  518  supply chemicals to the MOCVD chamber  502  and HVPE chamber  504  respectively. Reactive and carrier gases are supplied from the chemical delivery system through supply lines into a gas mixing box where they are mixed together and delivered to respective showerheads  1404  and  1304 . Generally supply lines for each of the gases include shut-off valves that can be used to automatically or manually shut-off the flow of the gas into its associated line, and mass flow controllers or other types of controllers that measure the flow of gas or liquid through the supply lines. Supply lines for each of the gases may also include concentration monitors for monitoring precursor concentrations and providing real time feedback, backpressure regulators may be included to control precursor gas concentrations, valve switching control may be used for quick and accurate valve switching capability, moisture sensors in the gas lines measure water levels and can provide feedback to the system software which in turn can provide warnings/alerts to operators. The gas lines may also be heated to prevent precursors and etchant gases from condensing in the supply lines. Depending upon the process used some of the sources may be liquid rather than gas. When liquid sources are used, the chemical delivery module includes a liquid injection system or other appropriate mechanism (e.g. a bubbler) to vaporize the liquid. Vapor from the liquids is then usually mixed with a carrier gas as would be understood by a person of skill in the art. 
     While the foregoing embodiments have been described in connection to a processing system that comprises one MOCVD chamber and one HVPE chamber, alternate embodiments may integrate one or more MOCVD and HVPE chambers in the processing system, as shown in  FIGS. 15 and 16 .  FIG. 15  illustrates an embodiment of a processing system  1500  that comprises two MOCVD chambers  502  and one HVPE chamber  504  coupled to the transfer chamber  506 . In the processing system  1500 , the robot blade is operable to respectively transfer a carrier plate into each of the MOCVD chambers  502  and HVPE chamber  504 . Multiple batches of substrates loaded on separate carrier plates thus can be processed in parallel in each of the MOCVD chambers  502  and HVPE chamber  504 . 
       FIG. 16  illustrates a simpler embodiment of a processing system  1600  that comprises a single MOCVD chamber  502 . In the processing system  1600 , the robot blade transfers a carrier plate loaded with substrates into the single MOCVD chamber  502  to undergo deposition. After all the deposition steps have been completed, the carrier plate is transferred from the MOCVD chamber  502  back to the loadlock chamber  508 , and then released toward the load station  510 . 
     A system controller  560  controls activities and operating parameters of the processing system  500 . The system controller  560  includes a computer processor and a computer-readable memory coupled to the processor. The processor executes system control software, such as a computer program stored in memory. Aspects of the processing system and methods of use are further described in U.S. patent application Ser. No. 11/404,516, filed Apr. 14, 2006, entitled EPITAXIAL GROWTH OF COMPOUND NITRIDE STRUCTURES, which is hereby incorporated by reference in its entirety. 
     The system controller  560  and related control software prioritize tasks and substrate movements based on inputs from the user and various sensors distributed throughout the processing system  500 . The system controller  560  and related control software allow for automation of the scheduling/handling functions of the processing system  500  to provide the most efficient use of resources without the need for human intervention. In one aspect, the system controller  560  and related control software adjust the substrate transfer sequence through the processing system  500  based on a calculated optimized throughput or to work around processing chambers that have become inoperable. In another aspect, the scheduling/handling functions pertain to the sequence of processes required for the fabrication of compound nitride structures on substrates, especially for processes that occur in one or more processing chambers. In yet another aspect, the scheduling/handling functions pertain to efficient and automated processing of multiple batches of substrates, whereby a batch of substrates is contained on a carrier. In yet another aspect, the scheduling/handling functions pertain to periodic in-situ cleaning of processing chambers or other maintenance related processes. In yet another aspect, the scheduling/handling functions pertain to temporary storage of substrates in the batch loadlock chamber. In yet another aspect the scheduling/handling functions pertain to transfer of substrates to or from the load station based on operator inputs. 
     The following example is provided to illustrate how the general process described in connection with processing system  500  may be used for the fabrication of compound nitride structures. The example refers to a LED structure, with its fabrication being performed using a processing system  500  having at least two processing chambers, such as MOCVD chamber  502  and HVPE chamber  504 . The cleaning and deposition of the initial GaN layers is performed in the HVPE chamber  504 , with growth of the remaining InGaN, AlGaN, and GaN contact layers being performed in the MOCVD system  502 . 
     The process begins with a carrier plate containing multiple substrates being transferred into the HVPE chamber  504 . The HVPE chamber  504  is configured to provide rapid deposition of GaN. A pretreatment process and/or buffer layer is grown over the substrate in the HVPE chamber  504  using HVPE precursor gases. This is followed by growth of a thick n-GaN layer, which in this example is performed using HVPE precursor gases. In another embodiment the pretreatment process and/or buffer layer is grown in the MOCVD chamber and the thick n-GaN layer is grown in the HVPE chamber. 
     After deposition of the n-GaN layer, the substrate is transferred out of the HVPE chamber  504  and into the MOCVD chamber  502 , with the transfer taking place in a high-purity N 2  atmosphere via the transfer chamber  506 . The MOCVD chamber  502  is adapted to provide highly uniform deposition, perhaps at the expense of overall deposition rate. In the MOCVD chamber  502 , the InGaN multi-quantum-well active layer is grown after deposition of a transition GaN layer. This is followed by deposition of the p-AlGaN layer and p-GaN layer. In another embodiment the p-GaN layer is grown in the HVPE chamber. 
     The completed structure is then transferred out of the MOCVD chamber  502  so that the MOCVD chamber  502  is ready to receive an additional carrier plate containing partially processed substrates from the HVPE chamber  504  or from a different processing chamber. The completed structure may either be transferred to the batch loadlock chamber  509  for storage or may exit the processing system  500  via the loadlock chamber  508  and the load station  510 . 
     Before receiving additional substrates the HVPE chamber and/or MOCVD chamber may be cleaned via an in-situ clean process. The cleaning process may comprise etchant gases which thermally etch deposition from chamber walls and surfaces. In another embodiment, the cleaning process comprises a plasma generated by a remote plasma generator. Exemplary cleaning processes are described in U.S. patent application Ser. No. 11/404,516, filed on Apr. 14, 2006, and U.S. patent application Ser. No. 11/767,520, filed on Jun. 24, 2007, titled HVPE SHOWERHEAD DESIGN, both of which are incorporated by reference in their entireties. 
     An improved system and method for fabricating compound nitride semiconductor devices has been provided. In conventional manufacturing of compound nitride semiconductor structures, multiple epitaxial deposition steps are performed in a single process reactor, with the substrate not leaving the process reactor until all of the steps have been completed resulting in a long processing time, usually on the order of 4-6 hours. Conventional systems also require that the reactor be manually opened in order to remove and insert additional substrates. After opening the reactor, in many cases, an additional 4 hours of pumping, purging, cleaning, opening, and loading must be performed resulting in a total run time of about 8-10 hours per substrate. The conventional single reactor approach also prevents optimization of the reactor for individual process steps. 
     The improved system provides for simultaneously processing substrates using a multi-chamber processing system that has an increased system throughput, increased system reliability, and increased substrate to substrate uniformity. The multi-chamber processing system expands the available process window for different compound structures by performing epitaxial growth of different compounds in different processing having structures adapted to enhance those specific procedures. Since the transfer of substrates is automated and performed in a controlled environment, this eliminates the need for opening the reactor and performing a long pumping, purging, cleaning, opening, and loading process. 
     Thus, a method of forming a nanocrystalline diamond-structured carbon layer on a silicon carbide layer has been described.