Patent Publication Number: US-2004050326-A1

Title: Apparatus and method for automatically controlling gas flow in a substrate processing system

Description:
FIELD OF THE INVENTION  
       [0001] This invention relates generally to semiconductor fabrication systems, and more specifically to a method and apparatus for delivering one or more gases to a substrate processing system.  
       BACKGROUND OF THE INVENTION  
       [0002] Semiconductor devices such as microprocessors and memories are fabricated by various processes, such as depositing a film on a substrate or etching portions of an existing film on a substrate. Of principal concern in many semiconductor manufacturing processes is the difficulty of maintaining process uniformity. For example, a layer deposited on a substrate may exhibit thickness variations across the substrate as well as composition variations within the deposited layer itself. As integrated circuit feature sizes become smaller, it is increasingly important to minimize these variations in order to achieve a deposited layer which exhibits very high thickness and composition uniformities.  
       [0003] Many semiconductor fabrication processes are activated thermally and/or via mass transport. As a result, maintaining optimal process uniformity typically requires adjustments to substrate temperature uniformity and/or gas flow distribution across the surface of the substrate. Prior art semiconductor processing equipment has utilized multi-zone heat sources to adjust the temperature distribution across a substrate in order to compensate for non-uniform mass transport effects. Additionally, prior art semiconductor processing equipment has featured means for distributing process gases according to a desired flow pattern in order to minimize mass transport effects across the surface of a substrate.  
       [0004] Chemical vapor deposition (CVD) processes are commonly used in semiconductor manufacturing to deposit a layer of material onto the surface of a substrate. In an epitaxial silicon or silicon-germanium deposition process, doped or undoped silicon layers are typically deposited onto a substrate using a low-pressure CVD process. In this process, a reactant gas mixture including a source of silicon and, optionally, a dopant gas is heated and passed over a substrate to deposit a silicon film on the substrate surface. The silicon source may be monosilane, dichlorosilane, trichlorosilane, or tetrachlorosilane; the dopant gas may be phosphine, arsine or diborane. Other silicon sources and dopants may also be used. In some instances, a non-reactant carrier gas, such as hydrogen, is also injected into the processing chamber, together with either or both of the reactant or dopant gases.  
       [0005] In a doped or undoped epitaxial silicon deposition process, the crystallographic nature of the deposited silicon is a function of the deposition temperature. Additionally, in some doped epitaxial silicon deposition processes, the temperature dependence of dopant incorporation into the film is inversely proportional to the temperature dependence of the epitaxial silicon deposition rate. As a result, adjusting the temperature distribution across a substrate to optimize the thickness uniformity of a doped epitaxial silicon layer may result in non-uniform dopant incorporation within the expitaxial silicon layer. In other CVD processes, adjusting the temperature distribution across a substrate may result in detrimental changes to electrical and/or physical properties of a deposited film.  
       [0006] U.S. Pat. No. 5,916,369 to Anderson et al. discloses a method and apparatus for controlling the flow rate and composition of a mixture comprising a silicon source gas and a dopant gas across a substrate surface. Referencing FIG. 2, a gas mixture containing a silicon source and a hydrogen carrier gas is injected into chamber  218  from gas sources  202  and  204 . Mass flow controllers  203  and  205  independently control the flow rate of the silicon source and the hydrogen carrier gas to chamber  218 . The gas mixture flows through two metering valves  211  and  212  which operate as variable restrictors to apportion the flow of silicon bearing gas between different gas inlet ports of chamber  218 . A dopant gas is fed from gas source  214 , through mass flow controllers  216  and  220 , and into the silicon source and hydrogen carrier gas mixture downstream of metering valves  211  and  212 . Mass flow controllers  216  and  220  may be used to independently control the dopant gas concentration flowing into different gas inlet ports of chamber  218 .  
       [0007] In Anderson et al., metering valves  211  and  212  each may comprise a valve containing a variable orifice which is manually adjusted to control the flow rate of gas passing through the valve body. Typically, a metering valve comprises a needle valve which is manually adjusted to vary flow restriction by the movement of a pointed plug or needle in an orifice or tapered orifice in the valve body. For example, metering valve  211  may be adjusted to have a greater flow restriction than metering valve  212  such that a greater proportion of gases from gas sources  202  and  204  pass through metering valve  212 . Alternatively, metering valve  212  may be adjusted to have a greater flow restriction than metering valve  211  such that a greater proportion of gases from gas sources  202  and  204  pass through metering valve  211 .  
       [0008] Typically, metering valves such as those described in Anderson et al. are manually adjusted to achieve optimal thickness and composition uniformity for a particular process. However, many applications require that different processes be performed within a single process chamber. Metering valve settings which have been optimized for one process may produce less than optimal results when used for another process, resulting in poor uniformity. Although metering valves may be adjusted to accommodate alternative processes, such adjustments may require excessive system downtime, resulting in undesirable delays.  
       [0009] Accordingly, a need has arisen for a system of supplying process gases to a semiconductor processing system which overcomes these problems. Such a gas distribution system may be useful in several different fabrication processes such as chemical vapor deposition, physical vapor deposition, etching, thermal annealing, thermal oxidation, and other such processes as are commonly used in the manufacture of integrated circuit devices. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0010] The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings.  
     [0011]FIG. 1 is a schematic diagram illustrating one embodiment of an apparatus for delivering fluids to a substrate processing system.  
     [0012]FIG. 2 is a schematic diagram illustrating one embodiment of a prior art apparatus for delivering fluids to a substrate processing system.  
     [0013]FIG. 3 is a schematic diagram illustrating one embodiment of a substrate processing system.  
     [0014]FIG. 4 is a schematic diagram illustrating one embodiment of a substrate processing chamber.  
     [0015]FIG. 5 is a schematic diagram illustrating one embodiment of a gas interface adapted to provide gas flow into a process chamber.  
     [0016]FIG. 6 is a schematic diagram illustrating one embodiment of a gas interface adapted to provide gas flow into a process chamber.  
     [0017]FIG. 7 is a schematic diagram illustrating one embodiment of a gas interface adapted to provide gas flow into a process chamber.  
     [0018]FIG. 8 is a schematic diagram illustrating one embodiment of a substrate processing chamber.  
     [0019]FIG. 9 is a schematic diagram illustrating one embodiment of a showerhead adapted to provide gas flow into a process chamber.  
     [0020]FIG. 10 is a schematic diagram illustrating one embodiment of an apparatus for delivering fluids to a substrate processing system.  
     [0021]FIG. 11 is a flow diagram illustrating one embodiment of performing a first process step and a second process step on a substrate.  
     [0022]FIG. 12A is a schematic diagram illustrating one embodiment of a metrology chamber for use with a processing system.  
     [0023]FIG. 12B is a schematic diagram illustrating one embodiment of a metrology chamber for use with a processing system.  
     [0024]FIG. 13 is a flow diagram illustrating one possible method of modifying computer controlled metering valve settings using measurements from a metrology chamber.  
     [0025]FIG. 14A is a graphical depiction of a process recipe.  
     [0026]FIG. 14B is a graphical depiction of another portion of the process recipe depicted in FIG. 14A.  
    
    
     SUMMARY OF THE INVENTION  
     [0027] A fluid delivery system for providing fluids to a substrate processing system is described herein. In one embodiment, the fluid delivery system may include a first manifold having a first inlet, a first outlet, and a second outlet, wherein the first outlet and the second outlet are coupled to the substrate processing system. The fluid delivery system may further include a first conduit for coupling a first fluid to the first inlet and a flow controller for controlling the flow of the first fluid through the first conduit. The fluid delivery system may also include a computer controlled metering valve coupled to the first outlet.  
     [0028] In another embodiment, the fluid delivery system may include a first manifold having a first inlet, a first outlet, and a second outlet, wherein the first outlet and the second outlet are coupled to the substrate processing system. The fluid delivery system may further include a first conduit for coupling a first fluid to the first inlet and a flow controller for controlling the flow of the first fluid through the first conduit. The fluid delivery system may also include a first metering valve coupled to the first outlet and a second metering valve coupled to the second outlet.  
     [0029] Additional features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows.  
     DETAILED DESCRIPTION OF THE INVENTION  
     [0030] The present invention describes a method and apparatus for delivering process fluids to a substrate processing system. In the following description, numerous specific details are set forth, such as specific materials, machines, and methods, in order to provide a thorough understanding of the present invention. However, one skilled in the art will appreciate that these specific details are not necessary in order to practice the present invention. In other instances, well known equipment features and processes have not been set forth in detail in order to not unnecessarily obscure the present invention.  
     [0031] A processing system having a computer controlled gas delivery system is described herein. The processing system may include a number of chambers for performing various processes involved in semiconductor fabrication. The processing system may include a process chamber for depositing layers of material onto a surface of a substrate held within the process chamber. The layers may be deposited, for example, by a process such as chemical vapor deposition. During a chemical vapor deposition process, a process gas is directed into an interior portion of a process chamber and over a surface of a substrate while the temperature of the substrate is maintained at a particular level, such that a layer is formed on the substrate as the process gas passes over the substrate.  
     [0032] The computer controlled gas delivery system described herein may be used to enhance the control and distribution of gases within a process chamber during substrate processing. For example, the gas delivery system may be used to control the concentration and flow rate of one or more process gases flowing over the surface of a substrate during a chemical vapor deposition process, thereby minimizing thickness and composition variations within a deposited layer.  
     [0033] Computer controlled metering valves and flow controllers may be used to control gas distribution and composition within a plurality of gas inlet manifold channels which direct one or more gases across the surface of a substrate. A system controller may execute a process recipe which contains settings for controlling the computer controlled metering valves and flow controllers. The system controller may automatically control the settings for the computer controlled metering valves and flow controllers based upon variables contained within the process recipe. Consequently, the computer controlled gas delivery system may be used to automatically alter the composition and flow rate of gases passing through the gas channels and across different portions of a substrate during processing.  
     [0034] The computer controlled gas delivery system may be used to automatically adjust computer controlled metering valve and flow controller settings while depositing multiple layers of varying composition and/or thickness over a substrate surface during a single process recipe. For example, a first layer may be deposited over a substrate surface using a first set of computer controlled metering valve and flow controller settings contained within a first process recipe step. Subsequent to depositing the first layer, a second set of computer controlled metering valve and flow controller settings may be accessed from a second process recipe step to deposit a second layer of material over the first layer. Consequently, the computer controlled gas delivery system may used to optimize gas distribution and composition at each process recipe step corresponding to a deposited layer, thereby minimizing thickness and composition variations within each layer.  
     [0035] Alternatively, the computer controlled gas delivery system may be used to deposit one or more layers of varying composition and/or thickness over separate substrates during separate processes. For example, a first set of computer controlled metering valve and flow controller settings may be accessed from a first process recipe to deposit one or more layers over a first substrate during a first process. Subsequently, a second set of computer controlled metering valve and flow controller settings may be accessed from a second process recipe to deposit one or more layers over a second substrate during a second process. As a result, the computer controlled gas delivery system may used to create an optimal gas distribution and composition for each process recipe, corresponding to maximum thickness and composition uniformities for each deposited layer.  
     [0036] The processing system may include a metrology device to measure the thickness and/or composition of a layer deposited on the surface of a substrate. The measurement may be taken at different locations along the surface of the deposited layer. Measurements taken by the metrology device may be used to automatically adjust computer controlled metering valve and flow controller settings in a process recipe to further improve thickness and/or composition uniformities in subsequent deposition processes.  
     [0037] The computer controlled gas delivery system of the present invention may provide significant benefits to a wide variety of processes commonly used in the manufacture of electronic devices. For example, in one embodiment the gas distribution system may be integrated with a chemical vapor deposition (CVD) processing system to control the concentration and flow rate of process gases over the surface of a substrate, thereby minimizing mass transport effects during processing and enhancing thickness and/or composition uniformity of a deposited layer. In alternative embodiments, the gas distribution system may be integrated with other types of processes, such as physical vapor deposition (PVD), etch, thermal anneal, thermal oxidation, and others to improve various process parameters and deposited material properties.  
     [0038] Processing System  
     [0039]FIG. 3 is a schematic diagram illustrating one embodiment of a substrate processing system  300  having a gas distribution system which is described herein. Processing system  300  may be a cluster processing tool, such as a Centura or Endura processing system manufactured by Applied Materials of Santa Clara, Calif. Processing system  300  may include one or more load-lock chambers  304 ; one or more process chambers  306 ,  308 , and  310 ; a metrology chamber  312 ; and a cooldown chamber  314 . Chambers  304 ,  306 ,  308 ,  310 ,  312 , and  314  may be attached to a central transfer chamber  302 . A substrate transfer robot may be located within transfer chamber  302  for transferring substrates between chambers  304 ,  306 ,  308 ,  310 ,  312 , and  314 .  
     [0040] Processing system  300  may further include a system controller  325  for controlling various operations of processing system  300 , power supplies  350  for supplying various forms of energy to processing system  300 , and pumps  375  for evacuating various vacuum chambers contained within processing system  300 .  
     [0041] System Controller  
     [0042] System controller  325  may control the operation of processing system  300 , including the operation of load-lock chambers  304 ; process chambers  306 ,  308 , and  310 ; metrology chamber  312 ; cooldown chamber  314 ; central transfer chamber  302 ; power supplies  350 ; and pumps  375 . System controller  325  may also control the operation of computer controlled metering valves and mass flow controllers structured to the computer controlled gas delivery system.  
     [0043] System controller  325  may include a single board computer (SBC) comprising a processor and memory. The SBC processor may include a central processing unit (CPU) such as a Pentium microprocessor manufactured by Intel Corporation of Santa Clara, Calif. In some embodiments, the SBC processor may include an application specific integrated circuit (ASIC) to operate one or more specific components of processing system  300 . For example, the SBC processor may include an ASIC to operate computer-controlled metering valves and mass flow controllers. The SBC memory may include various volatile and non-volatile memory devices, such as RAM or EPROMs.  
     [0044] System controller  325  may also include one or more memory storage devices, such as a hard disk drive, a floppy disk drive, or a CD-ROM drive. System controller  325  may further include one or more input/output (I/O) devices, such as a CRT monitor and keyboard; analog input/output boards; digital input/output boards; interface boards; and stepper motor controller boards. The SBC processor, SBC memory, memory storage devices, and input/output devices may communicate via a communications bus.  
     [0045] System Control Software  
     [0046] System controller  325  may control all of the activities of the processing system  300  according to an instruction set defined by system control software. The system control software may be stored in a computer-readable medium and executed by system controller  325 . Preferably, system control software is stored on a hard disk drive, but system control software may also be stored on a floppy disk, RAM, a CD-ROM or other types of memory storage devices. The system control software may be written in any conventional programming language, including but not limited to 68000 assembly language, C, C++, Pascal, or Fortran. In a preferred embodiment, the system control software comprises Legacy software developed by Applied Materials of Santa Clara, Calif.  
     [0047] The system control software may be entered into a single file or multiple files using a conventional text editor. If the system control software code is written in a high level language, the system control software code may be compiled, and the resulting compiler code may be linked with an object code of precompiled library routines. To execute the linked compiled object code, a user may invoke the object code, causing system controller  325  to load the code into SBC memory, from which the SBC processor reads and executes the code to perform the tasks identified in the system control software.  
     [0048] The system control software may include one or more sets of computer instructions for managing all operational aspects of processing system  300 . For example, the system control software may include computer instructions for managing the movement of wafer transfer mechanisms and the opening and closing of vacuum pump valves. In one embodiment, the system control software may include a chamber manager program for operating and managing priorities of the chamber components associated with process chambers  306 ,  308 , and  310 . The chamber manager program may contain a number of subroutines, such as a substrate positioning subroutine that controls substrate lifting mechanisms within a chamber. Thus, substrate position, chamber pressure, substrate temperature, power supply output, and other such parameters which affect processes performed within process chambers  306 ,  308 , and  310  may be controlled by the chamber manager program.  
     [0049] In one embodiment, the system control software may include a gas distribution program for operating a computer controlled gas delivery system. The gas distribution program may include instructions for controlling the settings of computer controlled metering valves, mass flow controllers, and isolation valves. Additionally, the system control software may include a process selector program that allows an operator to enter or select a process recipe and execute that process recipe in a particular process chamber.  
     [0050] It is to be understood that the system control software should not be limited to the specific embodiment of the various programs described herein, and that other sets of programs or other computer instructions that perform equivalent functions are within the scope of the present invention. Additionally, the separate programs described herein could be entirely integrated into a single program, or the tasks of one program could be integrated into the tasks of another program to provide a desired set of tasks.  
     [0051] Process Recipe  
     [0052] Instructions for directing a process chamber to perform a specific process on a substrate may be contained within a process recipe. A process recipe may comprise one or more process steps. Each process step may contain a set of variables that define various process parameters for that recipe step, such as but not limited to gas flow, step duration, microwave or RF bias power levels, magnetic field power levels, cooling gas pressure, chamber wall temperature, chamber pressure, substrate temperature, and susceptor position. Process parameters may be changed between process steps to vary the processing environment within a process chamber. The process recipe variables that define gas flow may include settings for computer controlled metering valves, mass flow controllers, and isolation valves. The valve settings may be stored in a table of valve setting instructions that lists valve settings inputted by a user. Alternatively, the table of valve settings may contain an algorithm for determining valve settings.  
     [0053] An example process recipe  1405  is depicted graphically in FIG. 14A. Process recipe  1405  contains three process steps: purge process step  1410 , ramp process step  1415 , and bake process step  1420 . Each of process steps  1410 ,  1415 , and  1420  contains variables that define various process parameters for each respective process step. For example, purge process step  1410  has a maximum step time of 5 seconds, ramp process step  1415  has a maximum step time of 90 seconds, and bake process step  1420  has a maximum step time of 45 seconds. Numerous other process parameters are contained within process recipe  1405 , such as temperature ramp rate, power supply output, and gas flows. Each these process parameters may be altered between process steps to vary the processing environment within a process chamber.  
     [0054] A process recipe may be stored as a table of process parameter settings on a memory storage device connected to system controller  325 , such as a hard drive. To execute a process recipe, the table of process parameter settings may be read into SBC memory and executed by a subroutine within the system control software to perform tasks identified within the process recipe steps. For example, during operation, the chamber manager subroutine program may monitor the various chamber components, determine which components need to be operated based on the process parameters contained within the process recipe, and direct the control of those components responsive to the monitoring and determining steps.  
     [0055] Process Sequence  
     [0056] Instructions for directing processing system  300  to perform a series of operations on a substrate may be contained within a process sequence. The operations may be performed in several different chambers within processing system  300 . A process sequence may comprise one or more sequence steps, and each sequence step may contain a process chamber designator and a process recipe designator. For example, a process sequence may include a first sequence step wherein a wafer is transferred from load-lock chamber  304  to designated process chamber  306  where a first process is performed on the wafer as defined by a designated first process recipe. The process sequence may include a second sequence step wherein a wafer is transferred from process chamber  306  to designated process chamber  308  where a second process is performed on the wafer as defined by a designated second process recipe. The process sequence may further include a third process sequence step wherein a wafer is transferred from process chamber  308  to load-lock chamber  304 . A process sequence may be stored on a memory storage device connected to system controller  325 , such as a hard drive. To execute a process sequence, the sequence may be read into SBC memory and executed by the system control software to perform the series of steps defined within the process sequence.  
     [0057] Prior to processing, a lot of substrates may be placed within load-lock chamber  304  and a process sequence may be assigned to each substrate within the lot of substrates. If each substrate is assigned the same process sequence, the same series of operations may be performed on each substrate. Alternatively, if substrates within the lot are assigned different process sequences, substrates within the lot will be processed differently according to their assigned process sequence.  
     [0058] After a process sequence has been assigned to each substrate within the lot of substrates to be processed, process system  300  may be instructed to process the lot of substrates according to each substrate&#39;s assigned sequence. A substrate transfer robot located within transfer chamber  302  may sequentially transfer substrates to a series of chambers as defined in the process sequence. For example, a process sequence may be assigned to each wafer within a lot of twenty-five wafers. Subsequently, the substrate transfer robot may transfer each wafer to one or more process chambers  306 ,  308 , and  310 ; a cooldown chamber  314 ; and then back to load-lock chamber  304 . Process chambers  306 ,  308 , and  310  may perform various processes on the wafer, such as deposition, etching, or annealing. Cooldown chamber  314  may be used to cool each wafer before returning the wafer to load-lock chamber  304 . After the lot of twenty-five wafers has been processed, load-lock chamber  304  may be vented to atmospheric pressure, opened, and the wafers may be removed for subsequent processing in other wafer processing systems.  
     [0059] System Software Operation  
     [0060] During operation, the process selector program is used to identify a process recipe and a process chamber in which the process recipe is to be performed. The process selector program code executes a designated process recipe by passing the process recipe parameters to the chamber manager program code, which controls multiple processing tasks in different process chambers according to the process recipe determined by the process selector program. The chamber manager program controls the execution of process recipes within the process chambers through instruction sets which control operation of the process chamber components. The chamber manager instruction sets may include, for example, a substrate positioning instruction set that controls robot components that load and remove a substrate onto a susceptor. The chamber manager instruction set may also include a pressure control instruction set that controls the evacuation of gas from a process chamber. A metrology program code may include instructions for taking surface uniformity measurements of a substrate by means of a metrology device, such as metrology chamber  312 .  
     [0061] During processing, the chamber manager program selectively calls the chamber component instruction sets in accordance with the particular process recipe being executed, schedules the chamber component instruction sets, monitors operation of the various chamber components, determines which components need to be operated based on the process parameters for the process recipe to be executed, and causes execution of a chamber component instruction set responsive to the monitoring and determining steps.  
     [0062] The gas distribution program code may include a valve setting instruction set for controlling settings of computer controlled metering valves, mass flow controllers, and isolation valves. Consequently, the gas distribution program code may be used to actuate the computer controlled metering valves, mass flow controllers, and isolation valves structured to the computer controlled gas delivery system.  
     [0063] A valve setting instruction set may be used to adjust valve settings for computer controlled metering valves from a table of valve settings entered into the process selector program code. The valve settings may include separate valve settings for different process recipes performed within a particular process chamber. The valve settings may also include separate valve settings for different layers that may be deposited on a substrate during a single process recipe. As a result, the valve setting instruction set may provide separate valve settings for each layer deposited onto a surface of a substrate. Consequently, uniformity may be optimized for each deposited layer.  
     [0064] The valve setting instruction set may adjust computer controlled metering valve settings based upon uniformity measurement taken during processing. For example, a metrology program may determine thickness uniformity of a deposited layer based upon output signals provided by metrology chamber  312  using, for example, Legacy software. The valve setting instruction set algorithm may subsequently calculate new computer controlled metering valve settings based upon the measured thickness uniformity. The new computer controlled metering valve settings may be incorporated into the table of valve settings using, for example, a SECS trace program. Using the new computer controlled metering valve settings, a process chamber may subsequently produce substrates having enhanced uniformity.  
     [0065] Process Chamber  
     [0066] Referencing FIG. 3, process chambers  306 ,  308 , and  310  may include a process chamber used to deposit layers over a substrate. The layers may be deposited by numerous processes such as chemical vapor deposition (CVD), physical vapor deposition (PVD), or other such processes as are commonly used in the fabrication of electronic devices. The gas distribution system of the present invention may be incorporated into a variety of substrate processing systems in order to enhance the control of two or more process gas flows within a process chamber. Alternatively, the gas distribution system may be used to enhance the control of one or more process gases flows and one or more inert gas flows within a process chamber. In the present invention, a process gas is defined as a gas or gas mixture which acts to deposit, remove, or treat a film on a substrate placed in a processing chamber. An inert gas is defined as a gas which is substantially non-reactive with chamber features and substrates placed in a deposition chamber at particular process temperatures.  
     [0067] For example, the gas distribution system of the present invention may be integrated with a chemical vapor deposition (CVD) processing system to control the flow of process gases over the surface of a substrate, thereby enhancing thickness and/or composition uniformity of a deposited layer. Alternatively, the gas distribution system may be integrated with a physical vapor deposition (PVD) processing system, an etch processing system, or any of a variety of other substrate processing systems as are commonly used in the manufacture of electronic devices.  
     [0068] For illustrative purposes, the gas distribution system of the present invention will be described herein in reference to a CVD processing system. In a typical CVD process, a process gas is passed through a process chamber and over a substrate. The substrate is maintained at a particular temperature such that a layer is formed on the substrate as the process gas passes over the substrate. Several varieties of CVD chambers are manufactured by Applied Materials of Santa Clara, Calif., including the Epi Centura, Epi xP Centura, and Epi Centura 300.  
     [0069] CVD Process Chamber with Side Gas Injection  
     [0070]FIG. 4 is a schematic diagram illustrating one embodiment of a CVD process chamber  400 . Process chamber  400  may be substantially similar to process chambers  306 ,  308 , and/or  310  described above in reference to FIG. 3. Process chamber  400  may include an upper dome  402 , a lower dome  404 , and a sidewall  406  positioned between upper dome  402  and lower dome  404 . Cooling fluid may be circulated through sidewall  406  to cool o-rings which seal upper dome  402  and lower dome  404  to sidewall  406 . An upper liner  408  and a lower liner  410  may be mounted against an inside surface of sidewall  406 . Upper dome  402  and lower dome  404  may be formed from a transparent material to allow heating light to pass through into process chamber  400 . An upper clamping ring  412  may extend around the periphery of an outer surface of upper dome  402 . A lower clamping ring  414  may extend around the periphery of an outer surface of lower dome  404 . Upper clamping ring  412  and lower clamping ring  414  may be secured together so as to clamp upper dome  402  and lower dome  404  to sidewall  406 .  
     [0071] A susceptor  416  may be located within process chamber  400 . Susceptor  416  may be adapted to removeably support a wafer in an approximately horizontal position. Susceptor  416  may extend transversely across process chamber  400  to divide process chamber  400  into an upper portion  418  above susceptor  416 , and a lower portion  420  below susceptor  416 . Susceptor  416  may be mounted on a shaft  422  that extends vertically downward from the center of the bottom surface of susceptor  416 . Shaft  422  may be connected to a motor that rotates shaft  422  and thereby rotates susceptor  416  and a wafer supported by susceptor  416 . An annular preheat ring  424  may be connected at its outer periphery to the inner periphery of lower liner  410  and may extend around susceptor  416 . Annular preheat ring  424  may be in the same plane as susceptor  416 , with the inner periphery of annular preheat ring  424  separated by a gap from the outer periphery of susceptor  416 .  
     [0072] In one embodiment, a plurality of lamps  426  may be mounted around process chamber  400 . Reflectors  428  may be located around lamps  426  to prevent energy radiated by lamps  426  from radiating away from process chamber  400 . Reflectors  428  may also be formed to reflect radiant energy towards upper dome  402  and lower dome  404 . Lamps  426  may radiate energy through the upper dome  402  and lower dome  404  to heat susceptor  416  and annular preheat ring  424 . Upper dome  402  and lower dome  404  may be made of a transparent material, such as quartz, so that energy radiated by lamps  426  may pass through upper dome  402  and lower dome  404 . In other embodiments, heating devices other than lamps, such as resistance heaters or RF inductive heaters, may be used to heat susceptor  416  and annular preheat ring  424 .  
     [0073] Susceptor  416  and annular preheat ring  424  may be formed from a material that is opaque to radiation emitted by lamps  426 , such as silicon carbide coated graphite. Thus, susceptor  416  and annular preheat ring  424  may be more readily heated by energy radiated from lamps  426 . A lower infrared temperature sensor  430 , such as a pyrometer, may be mounted below lower dome  404 , and may face the bottom surface of susceptor  416  through lower dome  404 . Lower infrared temperature sensor  430  may be used to monitor the temperature of susceptor  416  by receiving infrared radiation emitted from susceptor  416  when susceptor  416  is heated. An upper infrared temperature sensor  432  may be mounted above upper dome  402  facing the top surface of susceptor  416  through upper dome  402 . Upper infrared temperature sensor  432  may be used to monitor the temperature of a wafer supported by susceptor  416 .  
     [0074] Process chamber  400  may be a “cold wall” reactor wherein sidewall  406 , upper liner  408 , and lower liner  410  are at a substantially lower temperature than preheat ring  424  and susceptor  416  during processing. For example, in a process to deposit an epitaxial silicon film on a wafer, susceptor  416  and a wafer supported by susceptor  416  may be heated to a temperature of between 900-1200° C. The sidewall and liners may be maintained at a lower temperature of approximately 400-600° C. by cooling fluid circulated through sidewall  406 .  
     [0075] Process chamber  400  may include a gas interface  434  positioned in a side of process chamber  400 . Gas interface  434  may be adapted to transmit gases from one or more gas sources  436  into process chamber  400 . Gas sources  436  may include process gases and inert gases. Gas interface  434  may include a connector cap  440 , a baffle  442 , and an insert plate  444  positioned within sidewall  406 . Upper and lower fluid conduits  441  and  466  may be formed in connector cap  440  and insert plate  444 . Process chamber  400  may further include a passage  456  formed between upper liner  408  and lower liner  410 . Passage  456  may be fluidly connected to upper portion  418  of process chamber  400 . Process gas from gas sources  436  may pass through connector cap  440 , baffle  442 , insert plate  444 , and passage  456  into upper portion  418  of process chamber  400 .  
     [0076] During operation, one or more gases are supplied to gas interface  434  by means of inlet ports  450 . Gases from inlet ports  450  flow through connector cap  440  and bank against the upstream surface of baffle  442 . The gases are directed through holes formed in baffle  442  into upper and lower conduits  441  and  466  formed in insert plate  444 . Inlet ports  450 , connector cap  440 , baffle  442 , and upper and lower conduits  441  and  466  may form independent flow pathways for each gas entering process chamber  400 . As a result, each gas flowing into each inlet port and through connector cap  440 , baffle  442 , and insert plate  444  along upper and lower conduits  441  and  466  may be kept separate from other gases entering process chamber  400 . From upper conduits  441 , gases may flow across preheat ring  424 , susceptor  416  and a wafer supported by susceptor  416  in the direction indicated by arrows  486 . The gas flow profile from upper conduits  441 , across preheat ring  424  and a wafer may be predominantly laminar.  
     [0077] In one embodiment, process gases from lower conduits  466  and upper conduits  441  may both be directed into upper portion  418  of process chamber  400 . In an alternative embodiment, an inert gas may be directed through lower conduits  466  into lower portion  420  of process chamber  400 . For example, an inert purge gas such as hydrogen or nitrogen may be directed into lower portion  420  of process chamber  400  in order to prevent deposition on the back side of susceptor  416 . An inert purge gas may be fed into lower portion  420  at a rate which develops a positive pressure within lower portion  420  with respect to the process gas pressure in upper portion  418 , thereby preventing process gas from entering lower portion  420 .  
     [0078] Gases entering process chamber  400  from upper and lower conduits  441  and  466  may be evacuated from process chamber  400  through outlet  468 . Outlet  468  may be positioned in the side of process chamber  400  opposite gas interface  434 . Outlet  468  may include an exhaust passage  478  which extends from the upper chamber portion  418  to the outside diameter of sidewall  406 . Exhaust passage  478  may be coupled to outlet connector  490  on the exterior of sidewall  406 . Outlet connector  490  may be coupled to a vacuum source, such as a pump, by means of an exhaust foreline. The vacuum source may be used to create low or reduced pressure in chamber  400  during processing. Thus, process gas fed into process chamber  400  may be evacuated through exhaust passage  478  and outlet connector  490  into an exhaust foreline.  
     [0079]FIG. 5 illustrates one embodiment of gas interface  434  adapted to provide two gas flow channels into upper portion  418  of process chamber  400 . In this embodiment, gas interface  434  may include a first port  505  and a second port  510  connected to a first channel  507  and a second channel  512 , respectively. During substrate processing, a first gas flow entering first port  505  may flow through first channel  507  and across a first portion of a substrate positioned on susceptor  416 . Similarly, a second gas flow entering second inlet port  510  may flow through second channel  512  and across a second portion of the substrate.  
     [0080] In one embodiment, the flow of gas through first channel  507  may be controlled independently from the flow of gas through second channel  512 . Consequently, the flow of gas across first and second portions of a substrate positioned on susceptor  416  may be varied to more accurately control the uniformity of a layer deposited on the substrate. For example, a higher flow of gas may be directed through first channel  507  than through second channel  512  in order to increase the thickness uniformity of a particular deposited layer.  
     [0081]FIG. 6 illustrates another embodiment of gas interface  434  adapted to provide three gas flow channels into upper portion  418  of process chamber  400 . In this embodiment, gas interface  434  may include a central inlet port  605 , a first outside inlet port  610 , and a second outside inlet port  615  connect to a central channel  607 , a first outside channel  612 , and a second outside channel  617 , respectively. During substrate processing, a first gas flow entering central inlet port  605  may flow through central channel  607  and across a central portion of a substrate positioned on susceptor  416 . A second gas flow entering first outside inlet port  610  may flow through first outside channel  612  and across a first outside portion of the substrate. A third gas flow entering second outside inlet port  615  may flow through second outside channel  617  and across a second outside portion of the substrate.  
     [0082] In one embodiment, the flow of gas through central channel  607  may be controlled independently from the flow of gas through first outside channel  612  and second outside channel  617 . Consequently, the flow of gas across the central portion of a substrate positioned on susceptor  416  may be varied with respect to the flow of gas across the first and second outside portions of the substrate to more accurately control the uniformity of a layer deposited on the substrate. For example, a higher flow of gas may be directed through central channel  607  than through first outside channel  612  and second outside channel  617  in order to increase the thickness uniformity of a particular deposited layer.  
     [0083]FIG. 7 illustrates yet another embodiment of gas interface  434  adapted to provide five gas flow channels into upper portion  418  of process chamber  400 . In this embodiment, gas interface  434  may include a central inlet port  705 , a first middle inlet port  710 , a second middle inlet port  715 , a first outside inlet port  720 , and a second outside inlet port  725  connected to a central channel  707 , a first middle channel  712 , a second middle channel  717 , a first outside channel  722 , and a second outside channel  727 , respectively. During substrate processing, a first gas flow entering central inlet port  705  may flow through central channel  707  and across a central portion of a substrate positioned on susceptor  416 . A second gas flow entering first middle inlet port  710  may flow through first middle channel  712  and across a first middle portion of the substrate. A third gas flow entering second middle inlet port  715  may flow through second middle channel  717  and across a second middle portion of the substrate. A fourth gas flow entering first outside inlet port  720  may flow through first outside channel  722  and across a first outside portion of the substrate. A fifth gas flow entering second outside inlet port  725  may flow through second outside channel  727  and across a second outside portion of the substrate.  
     [0084] In one embodiment, the flow of gas through central channel  707 , first outside channel  722 , and second outside channel  727  may be controlled independently from the flow of gas through first middle channel  712  and second middle channel  717 . Consequently, the flow of gas across the central, first outside, and second outside portions of a substrate positioned on susceptor  416  may be varied with respect to the flow of gas across the first and second middle portions of the substrate to more accurately control the uniformity of a layer deposited on the substrate. For example, a higher flow of gas may be directed through central channel  707 , first outside channel  722 , and second outside channel  727  than through first middle channel  712  and second middle channel  717  in order to increase the thickness uniformity of a particular deposited layer.  
     [0085] The embodiments illustrated in FIGS. 5, 6, and  7  should not be interpreted as limiting as one of ordinary skill in the art will recognize that gas interface  434  may be structured to provide any number of gas flow channels into upper portion  420  of process chamber  400 . Additionally, the described gas flows are merely exemplary and other gas flows may be apportioned between different gas flow channels as required for particular processes.  
     [0086] CVD Process Chamber with Showerhead Gas Injection  
     [0087]FIG. 8 illustrates process chamber  800 , an alternative embodiment of a CVD process chamber. Process chamber  800  may be substantially similar to process chambers  306 ,  308 , and/or  310  described above in reference to FIG. 3. Process chamber  800  may include showerhead  815 , lower chamber wall  810 , and a sidewall  825  between showerhead  815  and lower chamber wall  810 . Cooling fluid may be circulated through sidewall  825  to cool o-rings which seal showerhead  815  and lower chamber wall  810  to sidewall  825 . An upper liner  830  and a lower liner  835  may be mounted against an inside surface of sidewall  825 . An upper clamping ring  840  may extend around the periphery of an outer surface of showerhead  815 . A lower clamping ring  845  may extend around the periphery of an outer surface of lower chamber wall  820 . Upper clamping ring  840  and lower clamping ring  845  may be secured together so as to clamp showerhead  815  and lower chamber wall  810  to sidewall  825 .  
     [0088] A susceptor  822  may be located within process chamber  800 . Susceptor  822  may be adapted to removeably support wafer  820  in an approximately horizontal position. Susceptor  822  may extend transversely across process chamber  800  to divide process chamber  800  into an upper portion  818  above susceptor  822 , and a lower portion  828  below susceptor  822 . Susceptor  822  may be mounted on a shaft  824  that extends vertically downward from the center of the bottom surface of susceptor  822 . An annular preheat ring  824  may be connected at its outer periphery to the inner periphery of lower liner  835  and may extend around susceptor  822 . Annular preheat ring  824  may be in the same plane as susceptor  822 , with the inner periphery of annular preheat ring  824  separated by a gap from the outer periphery of susceptor  822 . In one embodiment, susceptor  822  and annular preheat ring  824  may be heated by means of a resistance heater contained within susceptor  822 . In other embodiments, RF inductive heaters, lamps, or other such heating devices may be used to heat susceptor  822  and annular preheat ring  824 . The temperature of susceptor  822  may be monitored by means of a thermocouple embedded within susceptor  822 .  
     [0089] One or more process gases may be injected into upper portion  818  of process chamber  800  through a plurality of orifices  850  extending through a lower surface  855  of showerhead  815 . Orifices  850  may be arranged in a plurality of regions or zones on lower surface  855  of showerhead  815 . As shown in FIG. 9, orifices  850  may be arranged in a center region  905 , a middle region  910 , and an outer region  915 . Middle region  910  may be arranged in an annular configuration encircling center region  905  and outer region  915  may be arranged in an annular configuration encircling middle region  910  and extending adjacent to an outer periphery  920  of showerhead  815 .  
     [0090] Showerhead  815  may further include center passageway  907 , middle passageway  912  and outer passageway  917 . Orifices contained within center region  905  of showerhead  815  may connect with center passageway  907 . Similarly, orifices contained within middle region  910  may connect with middle passageway  912 . In like fashion, orifices contained within outer region  915  may connect with outer passageway  917 .  
     [0091] Process chamber  800  may further include a gas interface  875  positioned in a top portion of process chamber  800  and connected to showerhead  815 . Gas interface  875  may be adapted to direct gas from one or more gas sources through showerhead  815  and into upper portion  818  of process chamber  800 . Referencing FIG. 9, gas interface  875  may include center conduit  925 , middle conduit  930 , and outer conduit  935 . Center passageway  907  may be connected to center conduit  925 ; middle passageway  912  may be connected to middle conduit  930 ; and outer passageway  917  may be connected to outer conduit  935 . Center conduit  925  may be arranged coaxially along a portion of middle conduit  930  and outer conduit  935 . Similarly, middle conduit  930  may be arranged coaxially along a portion of outer conduit  935 .  
     [0092] Gas interface  875  may further include center inlet port  940 , middle inlet port  945 , and outer inlet port  950 . Center inlet port  940 , middle inlet port  945 , and outer inlet port  950  may be structured and arranged to provide process gas from one or more gas sources to gas interface  875 . Center inlet port may be connected to center conduit  925 ; middle inlet port  945  may be connected to middle conduit  930 ; and outer inlet port  950  may be connected to outer conduit  935 . Center inlet port  940 , middle inlet port  945 , and outer inlet port  950  may be connected to one or more gas supply lines, which are in turn connected to gas sources, such as gas cylinders.  
     [0093] As in the previous embodiment, process chamber  800  may be a “cold wall” reactor wherein sidewall  825 , upper liner  830 , and lower liner  835  are at a substantially lower temperature than preheat ring  824  and susceptor  822  during processing. Additionally, one or more channels  990  having an inlet  992  and an outlet  994  may be formed in showerhead  815 . A fluid may be directed into inlet  992 , through channels  990 , and out of outlet  994  to heat or cool showerhead  815  during operation of process chamber  800 .  
     [0094] In operation, one or more gases may be supplied to gas interface  875  through center inlet port  940 , middle inlet port  945 , and outer inlet port  950 . Gas from center inlet port  940  may flow through center conduit  925 , center passageway  907 , and orifices in center region  905  into upper portion  818  of process chamber  800 . Gas from middle inlet port  945  may flow through middle conduit  930 , middle passageway  912 , and orifices in middle region  910  into upper portion  818  of process chamber  800 . Gas from outer inlet port  950  may flow through outer conduit  935 , outer passageway  917 , and orifices in outer region  915  into upper portion  818  of process chamber  800 . Inlet ports  940 ,  945 , and  950 ; conduits  925 ,  930 , and  935 ; and passageways  907 ,  912 , and  917  may form independent flow pathways for each gas entering process chamber  800 . As a result, each gas flowing into each inlet port and through each conduit and passageway may be kept separate until the gases enter upper portion  818  of process chamber  800 .  
     [0095] Gases entering process chamber  800  from showerhead  815  may be evacuated from process chamber  800  through outlet  816 . Outlet  816  may be formed in lower chamber wall  810  of process chamber  800 . Outlet  816  may include an exhaust passage  804  which extends from lower chamber portion  828  to the lower surface of lower chamber wall  810 . Exhaust passage  804  may be coupled to outlet connector  806  on the exterior of lower chamber wall  810 . Outlet connector  806  may be coupled to a vacuum source, such as a pump, by means of an exhaust foreline. The vacuum source may be used to create low or reduced pressure in chamber  800  during processing. Thus, process gas fed into process chamber  800  may be evacuated through exhaust passage  804  and outlet connector  806  into an exhaust foreline.  
     [0096] Gas entering center inlet port  940  may initially contact a central portion of a substrate positioned on susceptor  822 ; gas entering middle inlet port  945  may initially contact a middle annular portion of the substrate; and gas entering outer inlet port  950  may initially contact an outer annular portion of the substrate. After entering upper portion  818  of process chamber  800 , process gases may flow radially across wafer  820 , susceptor  822 , and preheat ring  824 .  
     [0097] In one embodiment, the flow of gas through center inlet port  940  and outer inlet port  945  may be controlled independently from the flow of gas through middle inlet port  945 . Consequently, the flow of gas across the central and outer annular portions of a substrate positioned on susceptor  822  may be varied with respect to the flow of gas across the middle annular portion of the substrate to more accurately control the uniformity of a layer deposited on the substrate. For example, a higher flow of gas may be directed through the orifices in center region  905  and outer region  915  than through the orifices in middle region  910  in order to increase the thickness uniformity of a particular deposited layer.  
     [0098]FIG. 8 should not be interpreted as limiting as one of ordinary skill in the art will recognize that gas interface  875  may be structured to provide any number of gas flow channels into upper portion  818  of process chamber  800 . Additionally, the described gas flows are merely exemplary and other gas flows may be apportioned between different inlet ports and showerhead regions as required for particular processes.  
     [0099] Gas Delivery System  
     [0100] As previously discussed, a process chamber may include a gas interface adapted to provide multiple gas flow channels or regions to an interior portion of a process chamber and across portions of a substrate positioned in the process chamber. For example, FIG. 5 illustrates one embodiment of gas interface  434  adapted to provide two gas flow channels, FIG. 6 illustrates another embodiment of gas interface  434  adapted to provide three gas flow channels, and FIG. 7 illustrates yet another embodiment of gas interface  434  adapted to provide five gas flow channels. Similarly, FIG. 9 illustrates an embodiment of a gas interface  875  adapted to provide three gas flow regions within process chamber  800 .  
     [0101] In each of these examples, a gas delivery system may be arranged to direct one or more gases into each gas flow channel. One or more metering valves may be structured to the gas delivery system such that the total gas flow introduced into the gas delivery system may be apportioned between the gas flow channels. Consequently, the flow of gas over portions of a substrate positioned in a process chamber may be controlled with greater accuracy, thereby minimizing thickness and composition variations within layers deposited onto the surface of a substrate. For example, with respect to FIG. 6, one or more metering valves may be used to apportion a greater or lesser flow rate of gas through first outside channel  612  and second outside channel  617  than central channel  607  to increase the thickness uniformity of a particular layer deposited onto a substrate.  
     [0102] In the following descriptions, the term “manifold” is generally used to describe a plurality of conduits arranged to combine two or more fluid flow inlets into a single fluid flow outlet, or a plurality of conduits arranged to divide a single fluid flow inlet into two or more fluid flow outlets. Fluid flow conduits used to construct a manifold may be formed from a variety of materials as are commonly employed in semiconductor manufacturing systems, such as stainless steel high purity gaslines.  
     [0103] Gas Delivery System 1  
     [0104]FIG. 1 shows a schematic diagram illustrating one embodiment of a gas delivery system  100  for controlling the flow of gas to gas interface  105 . Gas interface  105  may include a first inlet port  106  and a second inlet port  108 . In one embodiment, gas interface  105  may be substantially similar to gas interface  434  in FIG. 5, which is structured to provide two gas flow channels into upper portion  418  of process chamber  400 . Consequently, during substrate processing, a first gas flow entering first inlet port  106  may be directed to flow across a first portion of a substrate contained within a process chamber and a second gas flow entering second inlet port  108  may be directed to flow across a second portion of the substrate.  
     [0105] Gas delivery system  100  may include a first gas source  110  and a first manifold  160 . First manifold  160  may include a first inlet  162 , a first outlet  164 , and a second outlet  166 . First inlet  162  of first manifold  160  may be coupled to first gas source  110 . First outlet  164  of first manifold  160  may be coupled to first inlet port  106  of gas interface  105 , and second outlet  166  of first manifold  160  may be coupled to second inlet port  108  of gas interface  105 .  
     [0106] A flow controller may be structured to gas delivery system  100  to control the flow of gas from gas source  110  through gas delivery system  100 . A first flow controller  112  may be positioned inline with first inlet  162  to control the flow rate of gas from first gas source  110  through first manifold  160 . In one embodiment, first flow controller  112  may be an automatic flow controller which provides closed loop flow control of gases passing through the automatic flow controller. For example, first flow controller  112  may be a computer controlled mass flow controller (MFC).  
     [0107] An MFC typically comprises an electronic control board, a thermal sensor, and a control valve. During operation, system controller  325  may direct an input signal representing an MFC setpoint to the electronic control board. The input signal received from system controller  325  causes the electronic control board to open the control valve, thereby allowing gas flow through the MFC. A portion of the gas flow through the MFC is directed across the thermal sensor, which generates an output signal proportional to the flow rate of the gas flowing through the MFC. The electronic control board monitors the thermal sensor output signal, compares it to the MFC setpoint, and adjusts the control valve to a setting that provides equalization between the setpoint and the thermal sensor output. Thus, an MFC provides a regulated and highly repeatable flow of gas by means of a closed loop mass flow control system. A wide variety of mass flow controllers are commonly available through manufacturers such as MKS, Horiba, and others to accommodate various fluid properties and fluid flow rates. Mass flow controller  112  is preferably a Series 8100 mass flow controller manufactured by Unit Instruments.  
     [0108] Gas delivery system  100  may also include one or more of isolation valves for controlling the flow of gas through portions of gas delivery system  100 . The term “isolation valve” is presently used to describe a valve which may be configured to either an ON or an OFF condition. An isolation valve configured to an ON position allows for the passage of gas through the valve. Conversely, an isolation valve configured to an OFF position prevents the passage of gas through the valve. An isolation valve is typically configured to an ON or OFF condition by means of a pneumatic or electrical input signal received from system controller  325 . An isolation valve may be either normally closed or normally open. A normally closed isolation valve is configured to an OFF condition in the absence of an input signal. A normally open isolation valve is configured to an ON condition in the absence of an input signal.  
     [0109] As shown in FIG. 1, isolation valves  113  may be arranged inline with first inlet  162  of first manifold  160  immediately upstream and immediately downstream of flow controller  112 . Isolation valves  113  may be selectively configured to control the flow of gas from gas sources  110  into first manifold  160 . Isolation valves  113  may include valves manufactured by Veriflo, Fujikin, Nupro, VAN, and Whitey among others.  
     [0110] Gas delivery system  100  may further include a first metering valve  178  positioned inline with first outlet  164  of first manifold  160 . First metering valve  178  may be adjusted to apportion the flow of gases passing through first manifold  160  between first outlet  164  and second outlet  166 . First metering valve  178  may be a valve containing a variable orifice which is adjusted to control the gas flow capacity of the valve, thereby altering the flow rate of gases passing through the valve body and first outlet  164 . In one embodiment, first metering valve  178  may be a needle valve which is manually adjusted to increase or decrease gas flow capacity by the movement of a pointed plug or needle in an orifice or tapered orifice in the valve body. A wide variety of manual needle valves are commercially available to accommodate various fluid properties and fluid flow rates.  
     [0111] In an alternative embodiment, first metering valve  178  may be a computer controlled metering valve which is adjusted by means of an output signal from a computer to control the flow rate of gas passing through first outlet  164 . For example, first metering valve  178  may comprise a computer controlled positioning mechanism connected to a variable orifice. The positioning mechanism may be, for example, a rotary stepper motor or a linear actuator which is actuated via an analog or digital voltage control signal to increase or decrease the size of the variable orifice. In one embodiment, system controller  325  may be used to control the operation of first metering valve  178 . First metering valve  178  is preferably not a closed loop flow control device, such as a mass flow controller, as first metering valve  178  is intended to apportion the total gas flow passing through flow controller  112  between first outlet  164  and second outlet  166 . In a preferred embodiment, first metering valve  178  may be a flowPoint metering valve manufactured by Applied Precision, Incorporated.  
     [0112] In one embodiment, gas delivery system  100  may be structured such that second outlet  166  is more restrictive to gas flow than first outlet  164  when first metering valve  178  is adjusted to a maximum flow capacity, and second outlet  166  is less restrictive to gas flow than first outlet  164  when first metering valve  178  is adjusted to a minimum flow capacity. In this embodiment, first metering valve  178  may be adjusted to increase the gas flow rate through first outlet  164 , thereby decreasing the gas flow rate through second outlet  166 . Similarly, first metering valve  178  may be adjusted to decrease the gas flow rate through first outlet  164 , thereby increasing the gas flow rate through second outlet  166 . As a result, first metering valve  178  may be adjusted to apportion the total gas flow entering first inlet  162  between first outlet  164  and second outlet  166 .  
     [0113] Various methods may be used to structure gas delivery system  100  such that second outlet  166  is more restrictive to gas flow than first outlet  164  when first metering valve  178  is adjusted to a maximum flow capacity and second outlet  166  is less restrictive to gas flow than first outlet  164  when first metering valve  178  is adjusted to a minimum flow capacity. In one embodiment, a fixed flow restrictor may be placed inline with second outlet  166  to achieve the desired flow restriction. For example, a high purity porous metal flow restrictor manufactured by Mott Corporation may be placed inline with second outlet  166  to “tune” the flow restriction to a desired amount. In an alternative embodiment, a manually adjustable needle valve may be placed inline with second outlet  166  to achieve the desired flow restriction. A wide variety of manual needle valves are commercially available to accommodate various fluid properties and fluid flow rates.  
     [0114] During substrate processing, isolation valves  113  may be configured to an ON condition, thereby allowing gas to flow from first gas source  110  through first flow controller  112 . First flow controller  112  may be configured to a first flow setpoint, thereby controlling the flow rate of gases passing through first manifold  160 . Gas from first gas source  110  may flow into first outlet  164  and second outlet  166  of first manifold  160 , into first inlet port  106  and second inlet port  108 , respectively. First metering valve  178  may be adjusted to increase the gas flow rate through first outlet  164 , thereby decreasing the gas flow rate through second outlet  166 . Alternatively, first metering valve  178  may be adjusted to decrease the gas flow rate through first outlet  164 , thereby increasing the gas flow rate through second outlet  166 . As a result, the gas flowing through first outlet  164  and second outlet  166  may be apportioned by adjusting first metering valve  178 , thereby increasing or decreasing the gas flow across a first and second portion of a substrate contained within a process chamber.  
     [0115] Consequently, gas delivery system  100  may allow for greater control over the flow of gas passing over first and second portions of a substrate positioned in a process chamber, thereby providing enhanced control over the thickness and composition of layers deposited on the substrate. For example, gas delivery system  100  may be integrated with a CVD processing system to apportion the flow of H 2  and TCS; H 2  and DCS; H 2 , GeH 4 , and SiH 4 ; or H 2  and SiH 4  across two different portions of a silicon wafer. Alternatively, gas delivery system  100  may be used to apportion the flow of H 2  and TCS; H 2  and DCS; H 2 , GeH 4 , and SiH 4 ; or H 2  and SiH 4  in combination with diborane, phosphine, or arsine across two different portion of a silicon wafer.  
     [0116] In the above description, gas delivery system  100  is structured to a gas interface  105  comprising two inlet ports  106  and  108 . However, it is to be noted that gas delivery system  100  may be adapted to flow one or more gases to a variety of gas interfaces corresponding to various process chamber configurations.  
     [0117] For example, in one embodiment gas delivery system  100  may be adapted to a gas interface such as gas interface  434  in FIG. 6 by dividing first outlet  164  into two conduits coupled to first outside inlet port  610  and second outside inlet port  615  and coupling second outlet  166  to central inlet port  605 . Alternatively second outlet  166  may be divided into two conduits which are coupled to first outside inlet port  610  and second outside inlet port  615  and first outlet  164  may be coupled to central inlet port  605 . In either configuration, first metering valve  178  may be used to apportion the gas flow between first outlet  164  and second outlet  166 , thereby increasing or decreasing the amount of gas passing across a central portion and first and second outside portions of a substrate.  
     [0118] In another embodiment, gas delivery system  100  may be adapted to a gas interface such as gas interface  434  in FIG. 7 by dividing first outlet  164  into three conduits which are coupled to first outside inlet port  720 , second outside inlet port  725 , and central inlet port  705 ; and second outlet  166  may be divided into two conduits which are coupled to first middle inlet port  710  and second middle inlet port  715 . Alternatively, second outlet  166  may be divided into three conduits which are coupled to first outside inlet port  720 , second outside inlet port  725 , and central inlet port  705 ; and first outlet  164  may be divided into two conduits which are coupled to first middle inlet port  710  and second middle inlet port  715 . In either configuration, first metering valve  178  may be used to apportion the gas flow between central, first outside, second outside first middle, and second middle portions of a substrate.  
     [0119] In yet another embodiment, gas delivery system  100  may be adapted to a gas interface such as gas interface  875  in FIG. 8 by dividing first outlet  164  into two conduits coupled to center inlet port  940  and outer inlet port  950  and coupling second outlet  166  to middle inlet port  945 . Alternatively second outlet  166  may be divided into two conduits which are coupled to center inlet port  940  and outer inlet port  950  and first outlet  164  may be coupled to middle inlet port  945 . In either configuration, first metering valve  178  may be used to apportion the gas flow between first outlet  164  and second outlet  166 , thereby increasing or decreasing the amount of gas passing across a central portion and middle and outer annular portions of a substrate.  
     [0120] Gas delivery system  100  may include one or more additional gas sources, flow controllers, and isolation valves connected to first inlet  162  of first manifold  160 . Gas delivery system  100  may also include a variety of inline filters, purifiers, pressure transducers, and other such devices as are commonly structured to substrate processing systems. These types of components have been omitted for illustrative purposes so as to not obscure the description of the present invention.  
     [0121] Gas Delivery System 2  
     [0122]FIG. 10 shows a schematic diagram illustrating another embodiment of a gas delivery system  1000  for controlling the flow of gas to gas interface  1005 . Gas interface  1005  may include a first inlet port  1006 , a second inlet port  1007 , and a third inlet port  1008 . In one embodiment, gas interface  1005  may be substantially similar to gas interface  434  in FIG. 6, which is structured to provide three gas flow channels into upper portion  418  of process chamber  400 . Consequently, during substrate processing, a first gas flow entering first inlet port  1006  may be directed to flow across a first outside portion of a substrate positioned on susceptor  416 ; a second gas flow entering second inlet port  1007  may be directed to flow across a second outside portion of the substrate; and a third gas flow entering third inlet port  1008  may be directed to flow across a central portion of the substrate.  
     [0123] Gas delivery system  1000  may further include a first gas source  1010 , a second gas source  1020 , a third gas source  1030 , a first manifold  1060 , a second manifold  1070 , and a third manifold  1075 . First manifold  1060  may include a first inlet  1061 , a second inlet  1063 , a third inlet  1065 , and a first outlet  1069 . Second manifold  1070  may include a fifth inlet  1071 , a second outlet  1072 , and a third outlet  1073 . Third manifold  1075  may include a sixth inlet  1076 , a fourth outlet  1080 , and a fifth outlet  1081 .  
     [0124] First inlet  1061 , second inlet  1063 , and third inlet  1065  of first manifold  1060  may be coupled to first gas source  1010 , second gas source  1020 , and third gas source  1030 , respectively. First outlet  1069  of first manifold  1060  may be coupled to fifth inlet  1071  of second manifold  1070 . Second outlet  1072  of second manifold  1070  may be coupled to sixth inlet  1076  of third manifold  1075 ; third outlet  1073  of second manifold  1070  may be coupled to third inlet port  1008 . Fourth outlet  1080  and fifth outlet  1081  of third manifold  1075  may be coupled to first inlet port  1006  and second inlet port  1007 , respectively.  
     [0125] Flow controllers may be structured to gas delivery system  1000  to manipulate the flow of gas through gas delivery system  1000 . A first flow controller  1012  may be positioned inline with first inlet  1061  to control the flow rate of gas from first gas source  1010  through first manifold  1060 . A second flow controller  1022  may be positioned inline with second inlet  1063  to control the flow rate of gas from second gas source  1020  through first manifold  1060 . A third flow controller  1032  may be positioned inline with third inlet  1065  to control the flow rate of gas from third gas source  1030  through first manifold  1060 . First flow controller  1012 , second flow controller  1022  and third flow controller  1032  each may comprise an automatic flow controller, such as a mass flow controller, which provides closed loop gas flow control. First flow controller  1012 , second flow controller  1022  and third flow controller  1032  are preferably Series  8100  mass flow controllers manufactured by Unit Instruments.  
     [0126] Gas delivery system  1000  may further include one or more isolation valves for controlling the flow of gas through portions of gas delivery system  1000 . As shown in FIG. 10, isolation valves  1013 ,  1023 , and  1033  may be arranged inline with first inlet  1061 , second inlet  1063 , and third inlet  1065  of first manifold  1060  immediately upstream and immediately downstream of flow controllers  1012 ,  1022 , and  1032  respectively. Isolation valves  1013 ,  1023 , and  1033  may be selectively configured to control the flow of gas from gas sources  1010 ,  1020 , and  1030  into first manifold  1060 . Isolation valves  1037  and  1039  may be arranged inline with fourth outlet  1080  and fifth outlet  1081  of third manifold  1075 , respectively, and isolation valve  1041  may be arranged inline with third outlet  1073  of second manifold  1070 . Isolation valves  1037 ,  1039 , and  1041  may be selectively configured to control the flow of gas from first manifold  1060  to first inlet port  1006 , second inlet port  1007 , and/or third inlet port  1008 , respectively. Isolation valves  1013 ,  1023 ,  1033 ,  1037 ,  1039 , and  1041  may include valves manufactured by Veriflo, Fujikin, Nupro, VAN, and Whitey among others.  
     [0127] Gas delivery system  1000  may further include a first metering valve  1078  and a second metering valve  1079  positioned inline with second outlet  1072  and third outlet  1073  of second manifold  1070 . Metering valves  1078  and  1079  may be used to apportion the flow of gases passing through fifth inlet  1071  of second manifold  1070  between second outlet  1072  and third outlet  1073 . For example, first metering valve  1078  and second metering valve  1079  may be adjusted so that a greater proportion of gases from fifth inlet  1071  will be diverted into third outlet  1073  than second outlet  1072 . Alternatively, first metering valve  1078  and second metering valve  1079  may be adjusted such that a greater proportion of gases from fifth inlet  1071  will be diverted into second outlet  1072  than third outlet  1073 .  
     [0128] First metering valve  1078  and second metering valve  1079  each may be a valve containing a variable orifice which is adjusted to control the gas flow capacity of the valve, thereby altering the flow rate of gases passing through the valve body. In one embodiment, first metering valve  1078  and second metering valve  1079  each may be a needle valve which is manually adjusted to increase or decrease gas flow capacity by the movement of a pointed plug or needle in an orifice or tapered orifice in the valve body. A wide variety of manual needle valves are commercially available to accommodate various fluid properties and fluid flow rates.  
     [0129] In an alternative embodiment, first metering valve  1078  and second metering valve  1079  each may be a computer controlled metering valve. For example, first metering valve  1078  and second metering valve  1079  may each comprise a computer controlled positioning mechanism connected to a variable orifice. The positioning mechanism may be, for example, a rotary stepper motor or a linear actuator which is actuated via an analog or digital voltage control signal to increase or decrease the size of the variable orifice. In one embodiment, system controller  325  may be used to control the operation of first metering valve  178 . First metering valve  1078  and second metering valve  1079  are preferably not closed loop flow control devices, such as a mass flow controllers, as first metering valve  1078  and second metering valve  1079  are intended to apportion the total gas flow passing through flow controller  112  between first outlet  164  and second outlet  166 . In a preferred embodiment, first metering valve  1078  may be a flowPoint metering valve manufactured by Applied Precision, Incorporated.  
     [0130] During substrate processing, isolation valves  1013 ,  1023 , and  1033  may each be configured to an ON condition, thereby allowing gas to flow from first gas source  1010 , second gas source  1020 , and third gas source  1030  through first flow controller  1012 , second flow controller  1022 , and third flow controller  1032 , respectively. First flow controller  1012  may be configured to a first flow setpoint, second flow controller  1022  may be configured to a second flow setpoint, and third flow controller  1032  may be configured to a third flow setpoint, thereby controlling the flow rate and composition of gases passing through first manifold  1060  and into second manifold  1070 . Gases from first gas source  1010 , second gas source  1020 , and/or third gas source  1030  may mix together within first manifold  1060  and subsequently enter fifth inlet  1071  of second manifold  1070 . The gas mixture comprising gas from first gas source  1010 , second gas source  1020 , and/or third gas source  1030  may then flow into second outlet  1072  and third outlet  1073  of second manifold  1070 .  
     [0131] From second outlet  1072  of second manifold  1070 , the gas mixture may flow into sixth inlet  1076  of third manifold  1075 . From sixth inlet  1076 , the gas mixture may flow through fourth outlet  1080  and fifth outlet  1081  of third manifold  1075  into first inlet port  1006  and second inlet port  1007 , respectively. From first outlet  1073  of second manifold  1070 , the gas mixture may flow into third inlet port  1008 .  
     [0132] The composition and flow rate of the gas mixture passing through first inlet port  1006 , second inlet port  1007 , and third inlet port  1008  may be altered by adjusting the flow setpoint of first flow controller  1012 , second flow controller  1022  and/or third flow controller  1032 . Additionally, first metering valve  1078  and second metering valve  1079  may be adjusted to apportion the gas flow from fifth inlet  1071  between second outlet  1072  and third outlet  1073 . For example, first metering valve  1078  and second metering valve  1079  may be adjusted such that second metering valve  1079  has a higher flow capacity than first metering valve  1078 . Consequently, a greater proportion of gases from fifth inlet  1071  will be diverted into third outlet  1073  than second outlet  1072 , thereby increasing the gas flow across a central portion of substrate contained within a process chamber and decreasing the gas flow across first and second outside portions of the substrate. Alternatively, first metering valve  1078  and second metering valve  1079  may be adjusted such that second metering valve  1079  has a lower flow capacity than first metering valve  1078 , thereby increasing the gas flow across first and second outside portions of a substrate and decreasing the gas flow across a central portion of the substrate.  
     [0133] Consequently, gas delivery system  1000  may allow for greater control over the flow of gas passing over central as well as first and second outside portions of a substrate positioned in a process chamber, thereby providing enhanced control over the thickness and composition of layers deposited on the substrate. For example, in one chemical vapor deposition process embodiment, first gas source  1010  may be H 2 , second gas source  1020  may be SiH 4 , and third gas source  1030  may be GeH 4 . In this embodiment, gas delivery system  1000  may be used to control the composition and flow rate of a mixture of H 2 , SiH 4 , and GeH 4  across different portions of a silicon wafer. In a second chemical vapor deposition process embodiment, first gas source  1010  may be H 2 , second gas source  1020  may be TCS, and third gas source  1030  may be a dopant such as diborane, phosphine, or arsine. In this embodiment, gas delivery system  1000  may be used to control the composition and flow rate of a mixture of H 2 , TCS, and a dopant across different portions of a silicon wafer. In a third chemical vapor deposition process embodiment, first gas source  1010  may be H 2 , second gas source  1020  may be DCS, and third gas source  1030  may be a dopant such as diborane, phosphine, or arsine. In this embodiment, gas delivery system  1000  may be used to control the composition and flow rate of a mixture of H 2 , DCS, and a dopant across different portions of a silicon wafer. In a fourth chemical vapor deposition process embodiment, first gas source  1010  may be H 2 , second gas source  1020  may be GeH 4 , and third gas source  1030  may be a dopant such as diborane, phosphine, or arsine. In this embodiment, gas delivery system  1000  may be used to control the composition and flow rate of a mixture of H 2 , GeH 4 , and a dopant across different portions of a silicon wafer. In a fifth chemical vapor deposition process embodiment, first gas source  1010  may be H 2 , second gas source  1020  may be SiH 4 , and third gas source  1030  may be a dopant such as diborane, phosphine, or arsine. In this embodiment, gas delivery system  1000  may be used to control the composition and flow rate of a mixture of H 2 , SiH 4 , and a dopant such as diborane, phosphine, or arsine across different portions of a silicon wafer.  
     [0134] In the above description, gas delivery system  1000  is structured to a gas interface  1005  comprising three inlet ports  1006 ,  1007 , and  1008 . However, it is to be noted that gas delivery system  1000  may be adapted to flow one or more gases to a variety of gas interfaces corresponding to various process chamber configurations.  
     [0135] For example, in one embodiment gas delivery system  1000  may be adapted to a gas interface such as gas interface  434  in FIG. 7 by dividing third outlet  1073  into three conduits which may be coupled to first outside inlet port  720 , second outside inlet port  725 , and central inlet port  705 ; fourth outlet  1080  and fifth outlet  1081  may be coupled to first middle inlet port  710  and second middle inlet port  715 . In this configuration, first metering valve  1078  and second metering valve  1079  may be adjusted to apportion the gas flow from fifth inlet  1071  between central inlet port  705 , first outside inlet port  720 , and second outside inlet port  725 ; and between first middle inlet port  710  and second middle inlet port  715 . Consequently, gas delivery system  1000  may be used to control the composition and gas flow rate across central, first outside, second outside, first middle, and second middle portions of a substrate, thereby providing enhanced control over the thickness and composition of layers deposited on the substrate.  
     [0136] In another embodiment, gas delivery system  1000  may be adapted to a gas interface such as gas interface  875  in FIG. 8, which is structured to provide three gas flow channels into an interior portion of process chamber  800  through showerhead  815 . For example, third outlet  1073  may be coupled to middle inlet port  945 . Similarly, fourth outlet  1080  and fifth outlet  1081  may be coupled to center inlet port  940  and outer inlet port  950 , respectively. In this configuration, first metering valve  1078  and second metering valve  1079  may be adjusted to apportion the gas flow from fifth inlet  1071  between center inlet port  940  and outer inlet port  950 ; and between middle inlet port  945 . Consequently, gas delivery system  1000  may be used to control the composition and gas flow rate across a central portion and middle and outer annular portions of a substrate, thereby providing enhanced control over the thickness and composition of layers deposited on the substrate.  
     [0137] Gas delivery system  1000  may also include a variety of inline filters, purifiers, pressure transducers, and other such devices as are commonly structured to substrate processing systems. These types of components have been omitted for illustrative purposes so as to not obscure the description of the present invention.  
     [0138] Processing Operation  
     [0139] As previously discussed in reference to FIG. 3, system controller  325  may control the operation of processing system  300  according to an instruction set defined by system control software. For example, system controller  325  may control all of the activities of processing chambers  306 ,  308 , and  310  by means of a chamber manager subroutine within the system control software.  
     [0140] System controller  325  may also control the distribution of gases to process chambers  306 ,  308 , and  310  by means of a gas distribution subroutine within the system control software. During processing, the gas distribution subroutine may instruct the system controller to monitor the isolation valves, flow controllers, computer controlled metering valves, and other such components which comprise the gas delivery system in order to determine which components need to be operated based upon the process parameters contained within a particular process recipe. The system controller may then direct the control of those components responsive to process recipe requirements.  
     [0141] During operation, a system operator may create a process recipe which contains all process parameters necessary to carry out a particular sequence of process steps within a process chamber. A process recipe is typically comprised of one or more process steps. Each process recipe step may contain a set of variables that define various process parameters for that recipe step, such as isolation valve, flow controller, and computer controlled metering valve setpoints. The process recipe variables may be stored in a table of instructions on a computer readable medium connected to system controller  325 . For example, computer controlled metering valve setpoints may be stored in a text table of valve setpoint instructions on a hard drive connected to system controller  325 . Alternatively, the table of instructions may contain an algorithm for determining computer controlled metering valve setpoints based upon other process parameter settings or data inputs.  
     [0142] The computer controlled gas delivery system of the present invention may be used to automatically adjust metering valve, flow controller and isolation valve settings between process recipes. For example, a first wafer may be processed using a first group of computer controlled metering valve and flow controller settings corresponding to a first process recipe. After the first wafer is removed from the process chamber, a second wafer may be processed using a second group of computer controlled metering valve and flow controller settings corresponding to a second process recipe.  
     [0143] Typically, metering valve setpoints which produce optimal uniformity for a first group of flow controller settings may produce less than optimal uniformity when used in conjunction with a second group of flow controller settings. However, the gas distribution system of the present invention may be used to automatically adjust computer controlled metering valve setpoints between process recipes, thereby allowing for optimal process uniformity while depositing layers with varying composition and/or thickness on different substrates using different process recipes. For example, a first process recipe may include a first group of metering valve settings which provides optimal uniformity across a first layer deposited using a first group of flow controller and isolation valve settings. A second process recipe may include a second group of metering valve settings which provides optimal uniformity across a second layer deposited using a second group of flow controller and isolation valve settings.  
     [0144] Additionally, the computer controlled gas delivery system of the present invention may be used to change process parameters between recipe steps in a single process recipe. As a result, the gas distribution subroutine may instruct the system controller to alter computer controlled metering valve, flow controller, and isolation valve settings responsive to process parameter changes between process recipe steps. FIG. 11 shows a flow diagram illustrating one embodiment of performing a first process step and a second process step on a substrate using the gas distribution system of the present invention. At step  1102 , the processing system may access a first group of valve settings for a first process step to be performed on the substrate. The first group of valve settings may include computer controlled metering valve, flow controller, and isolation valve setpoints corresponding to a first process step within a first process recipe. At step  1104 , the processing system may perform the first process step on the substrate using the first group of valve settings. At step  1106 , the processing system may access a second group of valve settings for a second process step to be performed on the substrate. The second group of valve settings may include computer controlled metering valve, flow controller, and isolation valve setpoints corresponding to a second process step within the first process recipe. At step  1108 , the processing system may perform the second process step on the substrate using the second group of valve settings. After the second process step is complete, the substrate may be removed from the process chamber and another substrate may be processed. In alternative embodiments, additional process steps may be performed on a substrate using additional process steps and valve settings within the first process recipe.  
     [0145] Typically, metering valve setpoints which produce optimal uniformity for a first group of flow controller settings may produce less than optimal uniformity when used in conjunction with a second group of flow controller settings. However, the gas distribution system of the present invention may be used to automatically adjust computer controlled metering valve setpoints between recipe steps in a single process recipe, thereby allowing for optimal process uniformity while depositing layers with varying composition and/or thickness over a substrate during a single process recipe. For example, a first recipe step may include a first group of metering valve settings which provides optimal uniformity across a first layer deposited using a first group of flow controller and isolation valve settings. A second recipe step may include a second group of metering valve settings which provides optimal uniformity across a second layer deposited using a second group of flow controller and isolation valve settings.  
     [0146] As previously discussed, an example process recipe  1405  is depicted graphically in FIG. 14A. Similarly, FIG. 14B graphically depicts inner metering valve setpoint  1425  and outer metering valve setpoint  1430  for purge process step  1410 . Hence, prior to performing process recipe  1405 , the processing system may access inner metering valve setpoints  1425  and outer metering valve setpoints  1430  and adjust corresponding computer controlled metering valves according to the voltage values contained within purge process step  1410 .  
     [0147] During operation, the gas distribution subroutine may direct system controller  325  to actuate one or more computer controlled metering valves by means of an output control signal. FlowPoint computer controlled metering valves manufactured by Applied Precision, Inc. provide for  256  discrete setpoints between 5% and 100% flow for a 0-10 Volt analog input signal. Hence, a system controller adapted to control one or more flowPoint computer controlled metering valves may generate a 0-10 Volt control signal for each flowPoint computer controlled metering valve structured to the gas distribution system. Other types of computer controlled metering valves may require alternative output signals, such as pneumatic, digital, or optical output signals.  
     [0148] In-Line Metrology  
     [0149] Referencing FIG. 3, processing system  300  may incorporate a metrology chamber  312  to measure film thickness uniformity of a wafer processed by process chambers  306 ,  308 , and  310 . FIGS. 12A and 12B are schematic diagrams illustrating one embodiment of a metrology chamber  1200  for use with processing system  300 . Metrology chamber  1200  may be substantially similar to metrology chamber  312  described above with reference to FIG. 3. Alternatively, metrology chamber  700  may be incorporated into cool-down chamber  314  attached to processing system  300 .  
     [0150] Referencing FIG. 12A, a reference sample  1202  may rest in a recess of a chuck  1204  that is part of a stage  1206  disposed within metrology chamber  1200 . A light source  1208  may provide a light signal  1210 , such as infrared radiation, that passes through a portion of chamber body  1212  to reference sample  1202 . After light signal  1210  reaches reference sample  1202 , a reflected light signal  1214  may be reflected towards a detector  1216 . Detector  1216  may be coupled to a computer system  1218 , which records the spectrum of the reference sample. Reference sample  1202  should not be set too deep in stage  1206  because the distance between light source  1208  and reference sample  1202  should be close to the distance between light source  1208  and a wafer  1220  placed within chamber body  1212  to ensure an accurate measurement. Computer system  1218  may be provided with a storage device, such as a hard drive, to store both a reference spectrum and a spectrum from each wafer  1220  that is measured. In addition, computer system  1218  may include a processor that executes an algorithm for comparing the reference sample spectrum with the spectrum from each wafer  1220  that is measured.  
     [0151] Although light source  1208  and detector  1216  are shown outside chamber body  1212 , it is to be appreciated that light source  1208  and detector  1216  can also be located within chamber body  1212 . Additionally, computer system  1218  may be integrated with metrology chamber  1200 , or it can be integrated within processing system  300 . For example, computer system  1218  may be integrated within system controller  325 .  
     [0152] During operation, a substrate which has been processed in at least one of process chambers  306 ,  308 , and  310  may be transferred to metrology chamber  312  by a substrate transfer robot. Metrology chamber  312  may measure one or more attributes of a layer deposited on the wafer, such as thickness uniformity, dopant incorporation, resistivity, and/or surface roughness. The substrate transfer robot may subsequently transfer the substrate to load-lock chamber  304  for removal from processing system  300 .  
     [0153] Computer controlled metering valve variables contained within a process recipe may be modified based upon measurements provided by metrology chamber  312 . FIG. 13 represents a flow diagram illustrating one possible method of modifying computer controlled metering valve variables using measurements from metrology chamber  312 . At step  1302 , processing system  300  determines the value of a computer controlled metering valve variable contained within a particular process recipe. At step  1304 , metrology chamber  312  measures the film thickness uniformity of a substrate processed by the process recipe. At step  1306 , the metrology chamber provides the measurements to the system controller, and system controller  325  modifies the computer controlled metering valve variable within the process recipe in order to optimize film thickness uniformity on subsequently processed substrates. System controller  325  may utilize various software programs and/or algorithms to modify computer controlled metering valve variables within process recipes.  
     [0154] Modifying computer controlled metering valve variables using measurements taken by in-line metrology chamber  312  may greatly enhance process uniformity on subsequently processed substrates, thereby automatically improving the process performance of processing system  300 . As processes are performed on successive substrates, computer controlled metering valve variables may be further modified to optimize process uniformity.  
     [0155] In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. However, it should be evident to one skilled in the art that various modifications and changes may be made without departing from the broader spirit and scope of the invention as set forth in the appended claims. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.