Patent Publication Number: US-2010116207-A1

Title: Reaction chamber

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      The present application claims priority to Provisional Application No. 61/112,604, filed Nov. 7, 2008, the entirety of which is hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a semiconductor processing system, and more particularly to a reaction chamber for use in a semiconductor processing system.  
      2. Description of the Related Art  
      In the processing of semiconductor devices, such as transistors, diodes, and integrated circuits, a plurality of such devices are typically fabricated simultaneously on a thin slice of semiconductor material such as a substrate, wafer, or workpiece. In one example of a semiconductor processing step during manufacture of such semiconductor devices, the substrate is typically transported into a reaction chamber in which a thin film, or layer, of a material is deposited on an exposed surface of the wafer. Once the desired thickness of the layer of semiconductor material has been deposited onto the surface of the substrate, the substrate is transported out of the reaction chamber for packaging or for further processing.  
      Known methods of depositing a film of a material onto a surface of a substrate include, but are not limited to: (atmospheric or low-pressure) vapor deposition, sputtering, spray-and-anneal, and atomic layer deposition. Chemical vapor deposition (“CVD”), for example, is the formation of a stable compound on a heated substrate by the thermal reaction or decomposition of certain gaseous compounds within a reaction chamber. The reaction chamber provides a controlled environment for safe deposition of stable compounds onto the substrate.  
      The type of reaction chamber used for a particular tool or process can vary depending upon the type of process being performed. One type of reaction chamber often used for CVD processes is a horizontal flow, cold-wall reaction chamber in which the reaction chamber includes a generally elongated chamber into which the substrate to be processed is inserted. Process gases are injected or introduced into one end of the reaction chamber and flow along the longitudinal length, across the substrate, and then exit the reaction chamber from the opposing end. When the process gases pass over the heated substrate within the reaction chamber, a reaction occurs at the surface of the substrate which causes a layer of material to be deposited onto the substrate.  
      As the gases flow along the length of a horizontal flow reaction chamber, the flow pattern may becomes uneven or localized areas of turbulence can be formed as a result of the gases contacting various structures within the reaction chamber, such as the susceptor, substrate, or the walls of the reaction chamber itself. When these localized areas of turbulence overlap with the surface of the substrate being processed, the uniformity of deposition across the surface of the substrate worsens. The localized areas of turbulence of the process gases that react with the substrate may cause bumps, ridges, or other localized deposition formations that reduce the uniformity of deposition. The profile of the surface of the substrate after deposition can be unpredictable due in part to the non-laminar and unstable flow of gases through the reaction chamber.  
      A need therefore exists for an improved reaction chamber that is tunable to reduce or eliminate the uneven or localized areas of turbulence of the flow of process gases through the reaction chamber to improve the uniformity of deposition, or produce a predictable deposition profile, on a substrate being processed.  
     SUMMARY OF THE INVENTION  
      In one aspect of the present invention, a reaction chamber is provided. The reaction includes an upper chamber having a stationary upper wall and a first inlet in fluid communication with the upper chamber. The first inlet is configured to allow at least one gas to be introducible into the upper chamber. The reaction chamber also includes a lower chamber having a lower wall. The lower chamber is in fluid communication with the upper chamber. The reaction chamber further includes a plate separating at least a portion of the upper chamber and at least a portion of the lower chamber. The plate is spaced apart from the upper wall by a first distance, and the plate is spaced apart from the lower wall by a second distance. An outlet is disposed opposite the first inlet. The upper chamber is tunable for producing a substantially stable and laminar flow of gases between the first inlet and the outlet by adjusting the first distance.  
      In another aspect of the present invention, a method for optimizing deposition uniformity on a substrate in a reactor of a semiconductor processing tool is provided. The method includes providing a split-flow reaction chamber. The split-flow reaction chamber comprises an upper chamber and a lower chamber, wherein the upper and lower chambers are at least partially separated by a plate, and gases are introducible into both the upper and lower chambers. The method further includes providing a susceptor located within the split-flow reaction chamber, wherein the susceptor is disposed between the upper and lower chambers. The susceptor is configured to support at least one substrate. The method further includes tuning dimensions of the split-flow chamber for producing substantially stable and laminar flow of gases within the upper chamber.  
      In still another aspect of the present invention, a reaction chamber is provided. The reaction chamber includes an upper wall, a lower wall, and a pair of opposing side walls connecting the upper and lower walls to define a reaction space therewithin. An inlet is located at one end of the reaction space, and an outlet is located at an opposing end of the reaction space. A velocity of at least one gas flowing through the reaction space is tunable by adjusting the upper wall relative to the lower wall to produce substantially stable and laminar flow of the at least one gas through the reaction space.  
      In yet another aspect of the present invention, a reaction chamber is provided. The reaction chamber includes a reaction space in which a substrate is supportable, and the reaction space has a volume. The reaction chamber also includes an inlet through which at least one gas is introducible into the reaction space, and an outlet through which gases within the reaction space exit the reaction space. The volume is tunable to provide substantially stable and laminar flow of gases through the reaction space.  
      In a further aspect of the present invention, a reaction chamber is provided. The reaction chamber includes a volume defined by a first wall, a second wall, opposing side walls, an inlet located at one end of the first and second walls, and an outlet located at an opposing end of the first and second walls. Gases are flowable through the volume at a first flow velocity. The first wall is adjustable to change the volume and such a change in the volume causes a corresponding increase or decrease in the first velocity resulting in a second velocity of the gases flowing through the volume. The second velocity of the gases flowing through the volume provides substantially laminar gas flow between the inlet and the outlet.  
      In another aspect of the present invention, a reaction chamber is provided. The reaction chamber includes a reaction space defined by a width, length, and height. The reaction chamber also includes a controller configured to produce a gas flow velocity of gases flowable through the reaction space. At least one of the width, length, and height is adjustable to produce substantially stable and laminar flow of said gases through the reaction space.  
      In another aspect of the present invention, a reaction chamber comprises an upper wall, a lower wall, a pair of opposing side walls connecting said upper and lower walls to define a reaction space therewithin, an inlet located at one end of said reaction space, and an outlet located at an opposing end of said reaction space. The upper wall is spaced from the lower wall by a first distance, the opposing side walls are spaced apart by a second distance, and the inlet and outlet are spaced apart by a third distance. At least one of the first, second, and third distances is selected by using modeling software to produce substantially stable and laminar flow of at least one gas through said reaction space.  
      Advantages of the present invention will become more apparent to those skilled in the art from the following description of the embodiments of the invention which have been shown and described by way of illustration. As will be realized, the invention is capable of other and different embodiments, and its details are capable of modification in various respects. Accordingly, the drawing(s) and description are to be regarded as illustrative in nature and not as restrictive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an isometric view of a semiconductor processing system.  
       FIG. 2  is a side cross-sectional view of a portion of the semiconductor processing system of  FIG. 1 .  
       FIG. 3  is a top view of a portion of the semiconductor processing system of  FIG. 2 .  
       FIG. 4  is a bottom isometric view of an embodiment of a reaction chamber.  
       FIG. 5  is a top isometric view of the reaction chamber of  FIG. 4 .  
       FIG. 6  is a side cross-sectional view of the reaction chamber, taken along line  6 - 6 ′ of  FIG. 3 .  
       FIG. 7  is a side cross-sectional view of another embodiment of a semiconductor processing system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Referring to  FIG. 1 , an exemplary embodiment of a semiconductor processing system  10  is shown. The semiconductor processing system  10  includes an injector assembly  12 , a reaction chamber assembly  14 , and an exhaust assembly  16 . The semiconductor processing system  10  is configured to receive a substrate  18  ( FIG. 2 ) to be processed within the reaction chamber assembly  14 . The injector assembly  12  is configured to introduce various gases into the reaction chamber assembly  14 , wherein at least one chemical reaction takes place within the reaction chamber assembly  14  between the gases introduced therein and the substrate  18  being supported therein. The unreacted process gases as well as the exhaust gases are then removed from the reaction chamber assembly  14  through the exhaust assembly  16 .  
      As shown in  FIGS. 1-2 , an embodiment of the injector assembly  12  includes a plurality of injectors  20  operatively connected to an inlet manifold  22 . In an embodiment, the inlet manifold  22  includes a first gas line  24  and a second gas line  26 . The first gas line  24  is configured to transfer gases from the injectors  20 , through the inlet manifold  22 , and to the upper portion of the reaction chamber  30  of the reaction chamber assembly  14 . The second gas line  26  is operatively connected to a gas source and is configured to transfer gases from the gas source, through the inlet manifold  22 , and to the lower portion of the reaction chamber  30  of the reaction chamber assembly  14 . It should be understood by one skilled in the art that the inlet manifold  22  may include any number of gas lines for carrying gases to be introduced into the reaction chamber  30 . In an embodiment, the exhaust assembly  16  is removably connected to the outlet  32  of the reaction chamber  30  of the reaction chamber assembly  14 .  
      In an embodiment, the reaction chamber assembly  14  includes a reaction chamber  30 , a substrate support assembly  34 , and a susceptor ring assembly  36 , as shown in  FIGS. 2-3 . The substrate support assembly  34  includes a susceptor  38 , a susceptor support member  40  operatively connected to the susceptor  38 , and a tube  42  operatively connected to the susceptor support member  40  and extending therefrom. During operation, a substrate  18  is supported on the susceptor  38 . The substrate support assembly  34  is rotatable for rotating the substrate  18  during operation if such rotation is desired for the deposition process.  
      In an embodiment, the susceptor ring assembly  36  includes a susceptor ring  44  and a susceptor ring support  46 , as illustrated in  FIGS. 2-3 . The susceptor ring  44  is configured to surround the susceptor  38  to eliminate or reduce the amount of heat loss from the outer radial edge of the susceptor  38  during processing. The susceptor ring support  46  extends from the lower surface of the reaction chamber  30  and is operatively connected to the susceptor ring  44  to maintain the susceptor ring in a substantially fixed location relative to the substrate support assembly  34 .  
      Referring to  FIGS. 2-6 , an exemplary embodiment of a reaction chamber  30  is shown. The illustrated reaction chamber  30  is a horizontal flow, single-pass, split flow, cold wall chamber. Although the illustrated reaction chamber  30  is illustrated as a split flow chamber, it should be understood by one skilled in the art that the improved reaction chamber  30  can be a split flow chamber or a single chamber. In an embodiment, the reaction chamber  30  is formed of quartz. The reaction chamber  30  illustrated in  FIGS. 1-2  is typically used for processes in which the pressure within the reaction chamber  30  is at or near atmospheric pressure. It should be understood by one skilled in the art that the concepts discussed below are in relation to the atmospheric reaction chamber  30  illustrated, but the same concepts can be incorporated into a reduced pressure reaction chamber in which the pressure within the reaction chamber is less than atmospheric pressure. The reaction chamber  30  includes an inlet  28 , an outlet  32 , and a reaction space  48  located between the inlet  28  and the outlet  32 . Both the inlet  28  and outlet  32  are surrounded by a flange  50 . The injector assembly  12  (FIG.  1 ) is operatively connected to the flange  50  surrounding the inlet  28 , and the exhaust assembly  16  ( FIG. 1 ) is operatively connected to the flange  50  surrounding the outlet  32 . The reaction chamber  30  includes an upper chamber  52  and a lower chamber  54 , wherein the upper chamber  52  is separated from the lower chamber  54  by a first plate  56  adjacent to the inlet  28  and by a second plate  58  adjacent to the outlet  32 . The first plate  56  is spaced apart from the second plate  58  longitudinally to allow room for the substrate support assembly  34  and the susceptor ring assembly  36  to be located therebetween. As illustrated in  FIG. 2 , the first plate  56 , second plate  58 , substrate support assembly  34 , and the susceptor ring assembly  36  define the demarcation between the upper and lower chambers  52 ,  54 . In an embodiment, the upper chamber  52  is in fluid communication with the lower chamber  54 . In another embodiment, the upper chamber  52  is substantially sealed from the lower chamber  54 .  
      In an embodiment, the reaction chamber  30  includes an upper wall  60 , a lower wall  62 , and opposing side walls  64  extending between the upper and lower walls  60 ,  62 , as illustrated in  FIGS. 2-6 . In an embodiment, the upper and lower walls  60 ,  62  are substantially parallel relative to each other. In another embodiment, the upper and lower walls  60 ,  62  are not parallel to each other. For example, in an embodiment, the upper wall  60  (not shown) is curved upwardly between the opposing side walls  64  such that the upper wall  60  has a semi-circular shape. In another embodiment, the upper wall  60  is angled upwardly from the opposing side walls  64  to form a longitudinal junction that is substantially parallel to the longitudinal axis of the reaction chamber  30 . It should be understood by one skilled in the art that the upper and/or lower walls  60 ,  62  of the reaction chamber  30  can be formed as planar or non-planar walls. It should also be understood by one skilled in the art that the upper wall  60  and the lower wall  62  may be formed having the same or a different shape. The upper wall  60 , lower wall  62 , and the side walls  64  extend between the opposing flanges  50  to form a volume within the reaction chamber  30 . The reaction space  48  is at least a portion of the total volume within the reaction chamber  30 , and process gases react with the substrate  18  disposed within the reaction space  48  to form a layer of deposition on the substrate  18 .  
      In an embodiment of a split flow reaction chamber  30 , as illustrated in  FIGS. 2-6 , the reaction space  48  is the volume generally defined by the upper wall  60 , first plate  56 , second plate  58 , substrate support assembly  34 , susceptor ring assembly  36 , side walls  64 , the inlet  28 , and the outlet  32 . The reaction space  48  is generally the volume defined within the upper chamber  52  of the split flow reaction chamber  30 . It should be understood by one skilled in the art that in an embodiment of a single-chamber reaction chamber  30  (not shown), the reaction space  48  is defined by the upper and lower walls  60 ,  62 , side walls  64 , inlet  28 , and the outlet  32 . The reaction space  48  of a single chamber reaction chamber  30  can be defined as the entire volume of the reaction chamber  30 . The reaction space  48  can also be defined as the volume immediately adjacent to the upper, exposed surface of the substrate  18  being processed. The reaction space  48  provides a volume in which the chemical reaction between the substrate  18  ( FIG. 2 ) and the process gases introduced into the reaction chamber  30  occurs.  
      In an embodiment, the first plate  56  is integrally formed with the side walls  64  of the reaction chamber  30 , as shown in  FIGS. 2-6 . In another embodiment, the first plate  56  is formed separately from the reaction chamber  30  and is inserted into the reaction chamber  30  during assembly thereof. When formed separately, the first plate  56  can be disposed, for example, on a pair of ledges (not shown) that are integrally formed with the side walls  64  of the reaction chamber  30 . In an embodiment, the first plate  56  is oriented in a substantially horizontal manner, or substantially parallel to the upper and lower walls  60 ,  62  of the reaction chamber  30 . In another embodiment, the first plate  56  is oriented at an angle relative to the upper and lower walls  60 ,  62 . In an embodiment, a lead edge of the first plate  56  is substantially aligned with the front surface of the flange  50  surrounding the inlet  28 . In another embodiment, the lead edge of the first plate  56  is spaced inwardly from the front surface of the flange  50  surrounding the inlet  28 . The first plate  56  provides a barrier between the upper and lower chambers  52 ,  54  adjacent to the inlet  28  of the reaction chamber  30 .  
      In an embodiment, the first plate  56  divides the inlet  28  to provide separate and distinct inlets into the upper and lower chambers  52 ,  54  of the reaction chamber  30 , as illustrated in  FIGS. 2-4  and  6 . In an embodiment, the inlet  28  can include an upper inlet  70  in fluid communication with the upper chamber  52  for introducing gases therein, and a lower inlet  72  in fluid communication with the lower chamber  54  for introducing gases therein. In an embodiment, the upper inlet  70  and/or the lower inlet  72  can be divided into multiple spaced-apart inlets, wherein each spaced-apart inlet introduces gases into the same chamber of the split flow reaction chamber  30 . In an embodiment, the lead edge of the first plate  56  is substantially aligned with the front surface of the flange  50  adjacent to the inlet  28  such that the first plate  56  contacts the inlet manifold  22  ( FIG. 2 ), thereby separating the gases from the first gas line  24  from the gases from the second gas line  26 .  
      In an embodiment, the second plate  58  is integrally formed with the side walls  64  of the reaction chamber  30 . In another embodiment, the second plate  58  is formed separately from the reaction chamber  30 , as illustrated in  FIGS. 2-3  and  6 , and is inserted into the reaction chamber  30  during assembly thereof. When formed separately, the second plate  58  can be disposed, for example, on a pair of opposing ledges  66  that are integrally formed with the side walls  64  of the reaction chamber  30 . In an embodiment, the second plate  58  is oriented in a substantially horizontal manner, or substantially parallel to the upper and lower walls  60 ,  62  of the reaction chamber  30 . In another embodiment, the second plate  58  is oriented at an angle relative to the upper and lower walls  60 ,  62 . In an embodiment, the second plate  58  extends from a position immediately adjacent to the trailing edge of the susceptor ring  44 . In an embodiment, a trailing edge of the second plate  58  is substantially aligned with the rear surface of the flange  50  surrounding the outlet  32 . In another embodiment, the trailing edge of the second plate  58  is spaced inwardly from the rear surface of the flange  50  surrounding the outlet  32 . The second plate  58  provides a barrier between the upper and lower chambers  52 ,  54  adjacent to the outlet  32  of the reaction chamber  30 .  
      In an embodiment, the edge of the second plate  58  directed toward the outlet  32  is spaced inwardly from the outlet  32  such that the outlet  32  includes a single aperture through which all of the gases introduced into the reaction chamber  30  from both the first gas line  24  and the second gas line  26  exit the reaction chamber  30 , as illustrated in  FIGS. 2 and 5 . In another embodiment, the rearwardly-directed surface of the second plate  58  is substantially coplanar with the flange  50  surrounding the outlet  32  such that the second plate  58  provides an upper outlet (not shown) and a lower outlet (not shown), wherein the gases introduced into the upper chamber  52  exit the reaction chamber  30  through the upper outlet and at least a portion of the gases introduced into the lower chamber  54  exit the reaction chamber  30  through the lower outlet.  
      In an embodiment, the second plate  58  includes a blocking plate  68  that extends downwardly therefrom, as shown in  FIG. 2 . The blocking plate  68  extends to a position adjacent to, or in contact with, the lower wall  62  of the reaction chamber  30 . In an embodiment, the blocking plate  68  extends substantially the entire distance between the opposing side walls  64 . In another embodiment, the blocking plate  68  extends only a portion of the width between the opposing side walls  64 . The blocking plate  68  is configured to block at least a portion of the gas flow within the lower chamber  54  between the inlet  28  and outlet  32 . In operation, the blocking plate  68  is further configured to create a pressure differential between the lower chamber  54  and the upper chamber  52  such that the pressure within the lower chamber  54  is greater than the pressure in the upper chamber  52 , thereby forcing at least a portion of the gases introduced into the lower chamber  54  to enter the upper chamber  52 . For example, gases within the lower chamber  54  can flow to the upper chamber  52  by flowing through gaps between the susceptor ring assembly  36  and the plates  56 ,  58 , or through a gap between the susceptor ring assembly  36  and the substrate support assembly  34 . By forcing at least a potion of the gases introduced into the lower chamber  54  to flow into the upper chamber  52 , the flow of gases into the upper chamber  52  reduces or eliminates potential flow of process gases from the upper chamber  52  into the lower chamber  54 .  
      The injectors  20  are configured to introduce at least one gas into the upper chamber  52  of a split flow reaction chamber  30 . The injectors  20  introduce the gases via the inlet  28  to produce a flow velocity of gases within the reaction space  48  between the inlet  28  and outlet  32  along a substantially horizontal flow path. In general, a computer-operated controller can be provided for controlling the gas flow from various sources, as well the injectors  20 . The injectors  20  are tunable, or adjustable, to produce different flow velocities within the reaction space  48 . The injectors  20  can be individually adjusted in order to modify or adjust the flow profile of gases exiting the injectors into the reaction chamber  30 . For example, the velocity of gases exiting each injector  20  may be the same or different so as to produce an overall flow profile of gases being introduced into the reaction chamber  30  from the inlet manifold  22  that has substantially stable and laminar flow between the inlet  28  and the outlet  32 . In an embodiment, the injectors  20  are adjustable to introduce gases into the upper chamber  52  of a reaction chamber  30  to produce a flow velocity of the gases between 5-100 cm/s for processes performed at substantially atmospheric pressure within the reaction chamber  30 , and more particularly between about 15-40 cm/s. In another embodiment, the injectors  20  are adjustable to produce a flow velocity of the gases between 20-25 cm/s for processes performed at substantially atmospheric pressure within the reaction chamber  30 . It should be understood by one skilled in the art that the flow velocity of gases through the reaction chamber  30  may be different for processes performed at reduced pressures, or pressures less than atmospheric pressure.  
      The improved reaction chamber  30  is configured to stabilize the gas flow, or to reduce and/or eliminate localized areas of turbulence of process gases between the inlet  28  and the outlet  32 , thereby increasing the uniformity of deposition on substrates  18  being processed within the reaction chamber  30 . The improved reaction chamber  30  is also configured to optimize the flow of gases through the reaction space  48  to improve the laminar flow of gases. This stabilized and laminar flow of gases between the inlet  28  and the outlet  32  results in a more uniform deposition across the surface of the substrate  18 . It should be understood by one skilled in the art that a more uniform deposition on substrates being processed will provide a deposition profile that, while not necessarily completely planar, will at least be a more predictable profile with a stable and laminar flow of gases across the surface of the substrate being processed. The improved reaction chamber  30  can be used to process any size substrates  18  including, but not limited to, 150 mm substrates, 200 mm substrates, 300 mm substrates, and 450 mm substrates. The dimensions of the reaction chamber  30  discussed below are directed to a reaction chamber  30  for processing 300 mm substrates, but it should be understood by one skilled in the art that the optimization techniques used to improve the laminar flow and uniform deposition within the reaction chamber for processing 300 mm substrates can likewise be used to improve the laminar flow of gases and the uniform deposition on the substrates in reaction chambers  30  configured to process other sizes of substrates.  
      In an exemplary embodiment of a split flow reaction chamber  30  for processing 300 mm substrates  18 , the reaction space  48  is at least a portion of the volume encompassed within the upper chamber  52 , as shown in  FIG. 2-3 . The opposing side walls  64  provide a width W therebetween, and the upper wall  60  provides a first height H 1  between the upper wall  60  and the first plate  56  and a second height H 2  between the upper wall  60  and the second plate  58 . In an embodiment, the first height H 1  between the upper wall  60  and the first plate  56  is the same as the second height H 2  between the upper wall  60  and the second plate  58 . In another embodiment, the first height H 1  between the upper wall  60  and the first plate  56  is different than the second height H 2  between the upper wall  60  and the second plate  58 . The width W between the opposing side walls  64  is wide enough to allow a susceptor  38  and susceptor ring  44  to be located therebetween. In an embodiment, the reaction space  48  has a substantially rectangular cross-section along the length of the reaction chamber  30  defined by the width W and the length between the flanges  50 , as illustrated in  FIG. 2 . Although the length and width of the reaction chamber  30  can be modifiable, it should be understood by one skilled in the art that these dimensions of the reaction chamber  30  would likely remain substantially constant between each reaction chamber  30  due to dimensional constraints of the tool into which the reaction chamber  30  would be installed.  
      In an embodiment, the upper wall  60  is integrally formed with the side walls  64  to define a portion of the upper chamber  52 . When the upper wall  60  is integrally formed with the side walls  64 , the upper chamber  52  is tunable to produce substantially stable and laminar flow of gases between the inlet  28  and outlet  32  within the upper chamber  52 . In an embodiment, the upper chamber  52  is tunable using a modeling program to model the gas flow within the upper chamber  52  to optimize the flow of gases through the upper chamber. In optimizing the flow of gases through the upper chamber  52  of the reaction chamber  30 , the first and second heights H 1 , H 2 , the width W, the length of the reaction space  48 , and/or the velocity of gases flowing between the inlet  28  and outlet  32  within the upper chamber  52  are modifiable. The modeling program can be used to pre-determine the dimensions of the upper chamber  52  to optimize the flow of gases therethrough. The modeling can also be used to pre-determine the gas velocity and flow profile of the gases introduced into the reaction chamber by the gas injectors  20 .  
      In an embodiment for tuning the upper chamber  52 , the dimensions of the upper chamber  52  are fixed and the velocity and flow profile from the injectors  20  is modeled to optimize the flow velocity from each injector  20  and the flow profile of gases exiting the inlet manifold  22  to provide substantially stable and laminar gas flow between the inlet  28  and the outlet  32 . In another embodiment for tuning the upper chamber  52 , the flow velocity from each injector  20  and the flow profile of gases exiting the inlet manifold  22  are fixed and the dimensions of the upper chamber  52  are modeled to optimize the dimensions to provide substantially stable and laminar gas flow between the inlet  28  and the outlet  32 .  
      In yet another embodiment for tuning the upper chamber  52 , the first and second heights H 1 , H 2  are modifiable while also modifying the flow velocity and profile of gases being introduced into the upper chamber  52 . The upper wall  60  of the reaction chamber  30  is modeled by adjusting the upper wall  60  to increase or decrease the first and second heights H 1 , H 2 . As the height of the upper wall  60  is adjusted relative to the first and second plates  56 ,  58 , the velocity of the gases exiting the injectors are also adjusted to maintain a pre-determined flow profile or to optimize the flow profile of gases exiting the inlet manifold  22 . For example, for a pre-determined flow velocity of process gases of about 20-25 cm/s through the upper chamber  52  that produces a substantially stable and laminar flow, as the upper wall  60  is modeled at a greater distance away from the first and second plates  56 ,  58 , the injectors  20  are adjusted to introduce more gases into the upper chamber  52  to maintain the pre-determined flow velocity of gases therethrough. The upper chamber  52  is tunable by comparing the flow pattern of the gases therethrough to optimize the first and second heights H 1 , H 2  to produce substantially stable and laminar flow at the pre-determined flow velocity. It should be understood by one skilled in the art that the dimensions of the upper chamber, the velocity of gases from the injectors  20 , the flow profile of gases exiting the inlet manifold  22 , or any combination thereof can be modified and modeled (e.g., using modeling software) to optimize the gas flow within the upper chamber  52  to provide a substantially stable and laminar flow of gases across the surface of the substrate being processed to produce a substantially uniform layer of material deposited on the substrate.  
      In one embodiment, the dimensions of the upper chamber  52  (or of the entire reaction chamber  30 ) are fixed during operation, and adjustment of the upper wall  60  is determined prior to operation by using modeling software to pre-determine dimensions of the reaction space  48 . In one embodiment, the upper wall  60  is moveable during processing, such as by using a ceiling insert  80  (described below) in conjunction with an automated position control system.  
      In embodiments employing a cross-flow reaction chamber  30  such as the reaction chamber illustrated in  FIG. 2 , in which the substrate  18  is transferred into the reaction chamber  30  from the upper inlet  70  on the front, optimizing the volume of the upper chamber  52  of the reaction chamber  30  can be accomplished by adjusting the relative distance between the upper wall  60  and the first and second plates  56 ,  58 . It should be understood by one skilled in the art that the first height H 1  should not be reduced such that the substrate  18  cannot be carried into the upper chamber  52  and disposed on the susceptor  38 . The first height H 1  should be at least large enough to allow an end effector (not shown) to be inserted and removed through the upper inlet  70 . However, for reaction chambers (not shown) in which the susceptor  38  is lowered such that the substrate  18  is disposed on the susceptor  38  at a position substantially below the first and second plates  56 ,  58 , the first and second heights H 1 , H 2  can be reduced until the first and second plates  56 ,  58  almost touch the upper wall  60  but still maintain a small gap between therebetween to allow process gases to flow through the upper chamber  52 .  
      In an embodiment, the upper chamber  52  is tunable by maintaining the upper wall  60  at a pre-determined location in which the first and second heights H 1 , H 2  remain fixed values and the injectors  20  are adjusted to modify the flow velocity and/or the flow profile introduced into the upper chamber  52 . The injectors  20  are adjusted to increase or decrease the flow velocity of gases through the inlet manifold  22  and into the upper chamber  52  and the resulting flow pattern through the reaction chamber is modeled.  
      In yet another embodiment, the upper chamber  52  is tunable by modeling the flow pattern of gases therethrough by adjusting the location of the upper wall  60  relative to the first and second plates  56 ,  58  to modify the first and second heights H 1 , H 2  as well as adjusting the injectors  20 , wherein the volume of the upper chamber  52  as well as the flow velocity and flow profile of gas introduced into the upper chamber  52  are optimized to produce a substantially stable and laminar flow of gases through the upper chamber  52 .  
      In an exemplary process of tuning the upper chamber  52  of a split flow reaction chamber  30  for processing 300 mm substrates, the upper wall  60  is spaced above the first and second plates  56 ,  58  to provide a first and second height H 1 , H 2  of about 1.2 inches (3.05 cm) and a width W between the opposing side walls  64  of about 17 inches (43.18 cm), wherein the volume of the upper chamber  52  is about 590 in 3  (9.67 liters). The fluid dynamic modeling, using a flow velocity of gases about 20-25 cm/s and the exemplary dimensions above, indicates a substantially stable and laminar flow is produced through the upper chamber  52 , thereby optimizing the uniformity of deposition on substrates processed within the reaction chamber  30 . In another exemplary process of tuning the upper chamber  52  of a split flow reaction chamber  30  for processing 300 mm substrates, the upper wall  60  is spaced above the first and second plates  56 ,  58  to provide a first and second height H 1 , H 2  of about 0.8 inches (2.03 cm) and a width between the opposing side walls  64  of about 17 inches (43.18 cm), wherein the volume of the upper chamber  52  is about 393 in 3  (6.44 liters). The fluid dynamic modeling, using a flow velocity of gases about 20-25 cm/s and the exemplary dimensions above, indicates a substantially stable and laminar flow is produced through the upper chamber  52 , thereby optimizing the uniformity of deposition on substrates processed within the reaction chamber  30 . It should be understood by one skilled in the art that any number of combinations of the first and second heights H 1 , H 2  and the flow velocity and flow profile introduced into the upper chamber  52  can be used to produce a substantially stable and laminar flow of gases through the upper chamber  52  to provide an optimized uniformity of deposition on the substrates being produced within the reaction chamber  30 .  
      Once the modeling of the upper chamber  52  to optimize the flow of gases therethrough to produce a substantially stable and laminar flow to produce more uniform deposition on substrates is completed, the reaction chamber  30  can be built to the dimensions determined during the modeling process. After the reaction chamber  30  is installed in a semiconductor processing system  10 , the injectors  20  are calibrated to the settings determined during the modeling process to produce the determined flow velocity and profile. It should be understood by one skilled in the art that further fine adjustments of the injectors  20  may be required to fully optimize the flow of gases through the upper chamber  52  to produce a more uniform deposition on substrates  18  being processed within the reaction chamber  30 .  
      In another embodiment, a ceiling insert  80  is inserted into the upper chamber  52  of the reaction chamber  30 , as illustrated in  FIG. 7 . The ceiling insert  80  provides an adjustable upper boundary to the reaction space  48  within the upper chamber  52 . The ceiling insert  80  is translatable relative to the first and second plates  56 ,  58 . In an embodiment, the ceiling insert  80  is manually adjustable to vary the heights H 1  and H 2 . In another embodiment, the ceiling insert  80  is mechanically adjustable by a mechanical adjuster (not shown) such that the ceiling insert  80  can be adjusted between cycles of processing substrates or during a substrate processing cycle. Persons of skill in the art will readily appreciate that there are a variety of different mechanical and/or electromechanical structures and means for adjusting the position of the ceiling insert  80  to vary the heights H 1  and H 2 , and that any of such structures and means can be employed, giving due consideration to any size and access constraints that may apply. The ceiling insert  80  is adjustable to increase or decrease the effective volume of the upper chamber  52  by preventing process gases from the injectors  20  to flow between the ceiling insert  80  and the upper wall  60  of the reaction chamber  30 . The upper chamber  52  is tunable by adjusting the relative position of the ceiling insert  80  to optimize the flow pattern of gases through the reaction space  48  to produce a substantially linear flow pattern between the inlet  28  and outlet  32 . The ceiling insert  80  allows the upper chamber  52  to be easily tunable for different processes or process recipes without requiring a completely new reaction chamber  30  to be produced and installed. The ceiling insert  80  can also be adjustable to control the front-to-back and/or side-to-side slope such that the ceiling insert  80  is not substantially parallel to the upper wall  60  or the first and second plates  56 ,  58 . The ability to adjust the ceiling insert  80  in this manner may aide in controlling or eliminating process depletion or other asymmetric effects within the upper chamber  52 .  
      In an embodiment, tuning the upper chamber  52  by using a ceiling insert  80  to optimize the uniformity of deposition on a substrate  18  includes processing a substrate  18  within the reaction chamber  30  to determine the uniformity of deposition on the substrate  18  when the ceiling insert  80  is at a first height H 1 . The ceiling insert  80  is then adjusted to a second height H 2 , and another substrate  18  is processed to determine a second uniformity of deposition on the substrate  18 . Further processing of substrates  18  may be performed to further optimize the flow velocity and flow profile of gas introduced into the reaction space  48  to produce a more uniform deposition on the substrates  18  being processed in the reaction chamber  30 . It should be understood by one skilled in the art that once the size and/or shape of the fully optimized upper chamber  52  is determined, the ceiling insert  80  may be fixed (i.e., non-moveable) within the reaction chamber  30  or the ceiling insert  80  may remain adjustable for further optimization of different processes or recipes within the reaction chamber  30 . It should also be understood by one skilled in the art that once the location of the ceiling insert  80  is determined to fully optimized upper chamber  52 , a reaction chamber  30  having an upper chamber  52  in which the upper wall  60  of the reaction chamber  30  is located at the position of the ceiling insert  80  in the fully optimized location can be produced and installed in semiconductor processing systems  10 .  
      While preferred embodiments of the present invention have been described, it should be understood that the present invention is not so limited and modifications may be made without departing from the present invention. The scope of the present invention is defined by the appended claims, and all devices, process, and methods that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein.