Patent Publication Number: US-2005139160-A1

Title: Clamshell and small volume chamber with fixed substrate support

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is a continuation of co-pending U.S. patent application Ser. No. 10/302,774, filed Nov. 21, 2002, which claims benefit of U.S. provisional patent application Ser. No. 60/352,190, filed Jan. 26, 2002. Each of the aforementioned related patent applications is herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      Embodiments of the present invention generally relate to a clamshell and small volume chamber with a fixed substrate support.  
      2. Description of the Related Art  
      Reliably producing sub-micron and smaller features is one of the key technologies for the next generation of very large scale integration (VLSI) and ultra large scale integration (ULSI) of semiconductor devices. However, as the fringes of circuit technology are pressed, the shrinking dimensions of interconnects in VLSI and ULSI technology have placed additional demands on the processing capabilities. The multilevel interconnects that lie at the heart of this technology require precise processing of high aspect ratio features, such as vias and other interconnects. Reliable formation of these interconnects is very important to VLSI and ULSI success and to the continued effort to increase circuit density and quality of individual substrates.  
      As circuit densities increase, the widths of vias, contacts, and other features, as well as the dielectric materials between them, decrease to sub-micron dimensions (e.g., less than 0.20 micrometers or less), whereas the thickness of the dielectric layers remains substantially constant, with the result that the aspect ratios for the features, i.e., their height divided by width, increase. Many traditional deposition processes have difficulty filling sub-micron structures where the aspect ratio exceeds 4:1. Therefore, there is a great amount of ongoing effort being directed at the formation of substantially void-free and seam-free sub-micron features having high aspect ratios.  
       FIG. 1  is a schematic cross-sectional view of a prior art processing chamber  100  defining a processing region  150 . An opening  112  in the chamber  100  provides access for a robot (not shown) to deliver and retrieve substrates  122  from the chamber  100 . A substrate support  124  supports the substrate  122  on a substrate receiving surface  126  in the chamber  100 . The substrate support  124  is mounted to a lift motor  130  to raise and lower the substrate support  124 . In one aspect, the lift motor  130  lowers the substrate support  124  to a substrate transferring position in which the substrate receiving surface  126  is below the opening  112  so that substrates  122  may be transferred to or from the substrate support  124 . In another aspect, the lift motor  130  raises the substrate support  124  to a deposition position in which the substrate  122  is in close proximity to a showerhead  140 . The showerhead  140  has a central gas inlet  144  for the injection of gases and has a plurality of holes  142  to accommodate the flow of gases therethrough to the substrate  122  disposed on the substrate support  124 .  
      One problem with the use of chamber  100  is aligning the substrate support  124  within the chamber  100 . The substrate support  124  may require removal so that the area under the substrate support  124  can be cleaned during routine maintenance. Reinstallation of the substrate support  124  requires aligning the substrate support  124  within the chamber  100 . Misalignment of the substrate support  124  may cause non-uniformity of processes performed in the chamber.  
      Thus, there is a need for an improved processing chamber useful for deposition processes such as atomic layer deposition and cyclical layer deposition.  
     SUMMARY OF THE INVENTION  
      Embodiments of the present invention generally relate to a clamshell and small volume chamber with a fixed substrate support. One embodiment of a processing chamber includes a fixed substrate support having a substrate receiving surface, a pumping ring disposed around a perimeter of the substrate receiving surface, and a gas distribution assembly disposed over the fixed substrate support. The pumping ring forms at least a portion of a pumping channel and has one or more apertures formed therethrough. The chamber may further include a gas-flow diffuser disposed radially inward of the apertures of the pumping ring.  
      Another embodiment of a processing chamber includes a first assembly comprising a fixed substrate support and a second assembly comprising a gas distribution assembly. The first assembly includes a first assembly body that is shaped and sized so that at least a portion of the first assembly body is below the substrate receiving surface of the substrate support. A hinge assembly couples the first assembly and the second assembly. The first assembly and the second assembly can be selectively positioned between an open position and a closed position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      So that the manner in which the above recited features of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
       FIG. 1  is a schematic cross-sectional view of a prior art processing chamber.  
       FIG. 2  is a schematic perspective view of one embodiment of a chamber of the invention in an open position.  
       FIG. 3  is a schematic perspective view of the chamber of  FIG. 2  in a closed position.  
       FIG. 4  is a schematic cross-sectional view of the bottom assembly of the chamber of  FIG. 2 .  
       FIG. 5  is a schematic cross-sectional view of one embodiment of a gas distribution assembly.  
       FIG. 6  is a schematic cross-sectional view of another embodiment of a gas distribution assembly.  
       FIG. 7  is a schematic cross-sectional view of another embodiment of a gas distribution assembly.  
       FIG. 7A  is a top cross-sectional view of the gas distribution assembly of  FIG. 7 .  
       FIG. 8  is a schematic cross-sectional view of another embodiment of a gas distribution assembly.  
       FIG. 9  is a schematic cross-sectional view of the top assembly and the bottom assembly in a closed position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       FIG. 2  is a schematic perspective view of one embodiment of a chamber  200  comprising a top assembly  210  and a bottom assembly  240  in an open position. The bottom assembly  240  includes a fixed substrate support  242  having a substrate receiving surface  244  to support a substrate thereon. The term “fixed substrate support” as used herein is defined to refer to a substrate support which is substantially non-moving vertically (i.e., a fixed elevation) during processing of substrates within the chamber. In some embodiments, the fixed substrate support may rotate and/or may move horizontally during processing of substrates. It is understood that a “fixed substrate support” may be repositioned, removed, or replaced from the chamber when substrate are not being processed within the chamber. The top assembly  210  includes a gas distribution assembly  212  to provide process gases (i.e. reaction gases, purge gases, and/or carrier gases) to the substrate support  242 .  
      The top assembly  210  and the bottom assembly  240  act as a “clamshell pair” which may be selectively moved between an open position and a closed position. An open position provides access for cleaning or replacing of interior components of the chamber  200 . In a closed position, the gas distribution assembly  210  is disposed over the substrate receiving surface  244  of the substrate support  242  for processing of substrates through the chamber  200 . In a closed position, a processing zone is defined between the substrate support  242  and the gas distribution assembly  212  and between the sidewall of the chamber  200 . The top assembly  210  and the bottom assembly  240  are coupled together with a hinge assembly  220 . The top assembly  240  includes a handle  222  to assist in moving the chamber  200  between an open position and a closed position.  
      As shown in this embodiment, the top assembly  210  includes a partial sidewall  236  and the bottom assembly  240  includes a partial sidewall  238 . The partial sidewall  236  of the top assembly  210  and the partial sidewall  238  of the bottom assembly  240  together form the sidewall of the chamber  200 . In one aspect when the chamber  200  is in an open position, the partial sidewall  238  of the bottom assembly  240  permits access below the substrate support  242  without having to remove the substrate support  242  and, thus, allows for simplified cleaning of areas underneath the substrate support  242 .  
       FIG. 3  is a schematic perspective view of the top assembly  210  and the bottom assembly  240  of  FIG. 2  in a closed position. The top assembly  210  may include one or more valves  230 , such as electronically controlled valves, pneumatically controlled valves, or other suitable valves, to deliver gases to the gas distribution system  212  (as shown in  FIG. 2 ). Preferably, the valves are three-port valves adapted to receive a flow of a reactant gas from a first port, adapted to receive a flow of a purge gas from a second port, and adapted to deliver the purge gas alone and in combination with the reactant gas to a third port. Preferably, the valves  230  are mounted to or in close proximity to a top surface of the top assembly  210  and may be mounted in any position (i.e., vertically, horizontally, or any position in between). The top assembly  210  may further include a gate valve  232  having an inlet adapted to be in fluid communication with a remote plasma source  234 . In one embodiment, the remote plasma source  234  is adapted to provide a plasma to the gas distribution assembly  212  (as shown in  FIG. 2 ) to clean chamber components. One example of a remote plasma source is an ASTRON™ remote plasma source available from by ASTeX of Woburn, Mass.  
       FIG. 4  is a schematic cross-sectional view of the bottom assembly  240  of  FIG. 2 . The upper surface of the body  241  of the bottom assembly  240  is angled so that one portion of the body  241   a  is above a plane of the substrate receiving surface  244  and one portion of the body  241   b  is below the plane of the substrate receiving surface  244 . The portion of the body  241   a  above the plane of the substrate receiving surface  244  forms the partial sidewall  238 . In one aspect, the portion of the body  241   b  below the plane of the substrate receiving surface permits access below the substrate support  242  by removing a pumping ring  270 , which is discussed in greater detail below. Since the area underneath the substrate support  242  may be accessed without having to remove the substrate support  242 , cleaning of this area is simplified.  
      The bottom assembly  240  may include a slit valve  266  located in the portion of the body  241   a  above the plane of the substrate receiving surface  244  to provide access for a robot to deliver and retrieve substrates from the chamber. Alternatively, the top assembly  210  may include a slit valve. In either case, the slit valve  266  is preferably adapted to provide access for a thin wrist robot so that the volume of the processing zone defined between the substrate support  242  and the gas distribution assembly  212  may be reduced.  
      Lift pins  252  are movably disposed through the substrate support  242  to raise and lower a substrate over the substrate receiving surface  244 . A lift plate  254  connected to a lift motor  256  may be mounted to the bottom assembly  240  to raise and lower the lift pins  252 . The substrate support  242  may be adapted to secure a substrate thereon using a vacuum chuck. For example, the substrate receiving surface  244  may include raised areas  246  (i.e., bumps) adapted to support a substrate thereon and may include recessed areas  248  (i.e., grooves) adapted to support a low pressure region via fluid communication with a vacuum supply from a vacuum introduced through a port  250 . Alternatively or in addition, the port  250  may provide a backside gas to enhance thermal conduction between the substrate support  242  and a substrate disposed thereon. The substrate support may also be adapted to hold a substrate thereon, by other techniques. For example, the substrate support may include an electrostatic chuck. The substrate support  242  may be heated using an embedded heated element  258  to heat a substrate disposed thereon. The substrate support may also be heated using other heating sources, such as heating lamps disposed above and/or below the substrate. A purge member  260 , such as a purge ring, may be positioned on or adjacent the substrate support  242  to form an annular purge gas channel  262 . A purge gas conduit  264  is formed through the substrate support  242  and the stem  243  of the substrate support  242 . The purge gas conduit  264  is in fluid communication with a purge gas supply to provide a purge gas to the annular purge gas channel  262 . A purge gap  263  between the purge member  260  and the substrate support  242  directs the purge gas to a perimeter portion of the substrate supporting surface  242  to help prevent deposition at the edge and/or backside of the substrate.  
      The bottom assembly  240  may further include a pumping ring  270  which defines an upper surface of a pumping channel  272 . The pumping ring  270  may be an annular member or any other shape depending on the shape of the substrate receiving surface  244 . The pumping channel  272  is in fluid communication with a pumping port  276  coupled to a vacuum source  278 . In one embodiment, the pumping port  276  is located adjacent one side of the chamber  200 . The pumping ring  270  includes a plurality of apertures  274  formed therethrough for the flow of gases from the processing zone to the pumping channel  272  and then, from the pumping channel  272  to the pumping port  276  exiting the chamber  200 . Preferably, the upper surface of the pumping channel  272  is disposed below a plane of the substrate receiving surface  244 . As shown in this embodiment, the apertures are uniformly sized and uniformly spaced around the pumping ring  270 . In other embodiments, the size, the number, and the position of the apertures  274  in the pumping ring  270  may vary depending on the desired flow pattern of gases across the substrate receiving surface  244 . For example, the apertures  274  may be adapted to help provide a uniform pressure drop around the perimeter of the substrate receiving surface  244 . In one example, the size of the apertures  274   a  in close proximity to the pumping port  276  may be smaller than the size of the apertures  274   b  farther from the pumping port  276 . In another example, the apertures  274  are uniformly size and are positioned in greater number farther from the pumping port  276 .  
      In one aspect, the diameter of each aperture  274  is preferably greater than the depth of the aperture  274  so that the diameter of each aperture  274  controls restriction of gas flow therethrough rather than the depth of the aperture  274 . In another aspect, the total cross-sectional area of the apertures  274  is less than the cross-sectional area  277  of the pumping port  276  so that apertures  274  choke the flow of gas flow therethrough to the pumping port  276 . Preferably, the total cross-sectional area of the apertures  274  is between about {fraction (1/10)} and about ⅓ the cross-sectional area  277  of the pumping port  276 . In general, the total cross-sectional area of the apertures  274  for a chamber operated at a low pressure is greater than the total cross-sectional area of apertures  274  for a chamber operated at a high pressure.  
      A gas-flow diffuser  280  may be disposed on the pumping ring  270  radially inward of the apertures  274  to change the flow path of gases to the apertures  274 . As shown in  FIG. 2  and  FIG. 4 , the gas-flow diffuser  280  extends partially around the substrate receiving surface  244  and is tapered from its highest height proximate apertures  274   a  adjacent the pumping port  276 . In one aspect, the gas-flow diffuser  280  extends partially around the substrate receiving surface  244  to allow for transport of a substrate between the slit valve  266  and the lift pins  252 . In other embodiments, the gas-flow diffuser  280  may extend entirely around the substrate receiving surface  244 . In addition, the height of the gas-flow diffuser  280  may vary along its length in steps and/or in tapered segments. Alternatively, the gas-flow diffuser may have a uniform height. At least a portion of the gas-flow diffuser  280  extends above a plane defined by the substrate receiving surface  244 . Not wishing to be bound by theory, it is believed that the gas-flow diffuser  280  helps provide a uniform pressure drop around the substrate receiving surface  244 .  
      In one embodiment, the substrate support  242  is sized and shaped to provide a gap  284  between the substrate support  242  and the pumping ring  270 . The width of the gap  284  may be selected to control heat transfer between the substrate support  242  and the pumping ring  270 , to control the flow of purge gas between the substrate support  242  and pumping ring  270 , and/or to allow for thermal expansion of the substrate support  242 . In one embodiment, the width of the gap  284  is between about 0.03 inches and about 0.12 inches. A purge gas port  286  may be disposed below the substrate support  242  to provide a bottom purge gas which flows through the gap  284  to the apertures  274  to prevent the flow of process gases below the substrate support  242  and prevent gases from entering and depositing in the area below the substrate support  242 . In one embodiment, the purge gas port  286  is adapted to provide a bottom purge gas to a higher pressure than the pressure in the processing zone defined between the substrate support  242  and the gas distribution assembly  212 .  
      In reference to  FIG. 2 , the bottom surface of the body  211  of the top assembly  210  is angled to match the angled upper surface of the body  241  of the bottom assembly  240 . The gas distribution assembly  212  may be any suitable gas distribution apparatus or showerhead.  FIG. 5  is a schematic cross-sectional view of one embodiment of gas distribution assembly  212 A. The gas distribution system illustrated in  FIG. 5  is more fully described in U.S. patent application (Ser. No. 10/032,293) entitled “Chamber Hardware Design For Titanium Nitride Atomic Layer Deposition” to Nguyen et al. filed on Dec. 21, 2001, which is incorporated by reference in its entirety to the extent not inconsistent with the present disclosure.  
      Gas distribution assembly  212 A comprises a lid plate.  522  and a distribution plate  530  disposed below the lid plate  522  which provide one or more isolated zones/flow paths therethrough. As shown in  FIG. 5 , a first flow path is provided through an outlet gas channel  554 A formed through the lid plate  554  and through centrally located openings  531 A and  531 B formed through the distribution plate  530  to the processing zone. An inner diameter of the gas channel  554 A gradually increases within the lid plate  522  to decrease the velocity of the flow of gas therethrough. A dispersion plate  532  is also disposed adjacent the openings  531 A,  531 B to prevent the flow of gas therethrough from impinging directly on the substrate surface by slowing and re-directing the velocity profile of the flowing gases. Without this re-direction, the force asserted on the substrate by the flow of gas through the first flow path may prevent deposition because the kinetic energy of the impinging gas may sweep away reactive molecules already disposed on the substrate surface. A second flow path is provided through an outlet gas channel  554 B formed through the lid plate  554 , through a cavity  556  formed between the lid plate  554  and distribution plate  530 , and through apertures  533  formed in the distribution plate  530 . The position of the apertures  533  may vary along the cavity  556 . Different valves are coupled to the outlet gas channel  554 A and the outlet gas channel  554 B to provide a first gas through the first flow path and to provide a second gas through the second flow path. In other embodiments, the lid plate  522  and the distribution plate  530  may be adapted to provide one flow path or more than two flow paths.  
       FIG. 6  is a schematic cross-sectional view of another embodiment of a gas distribution system  212 B. The gas distribution system  212 B is shown and described in U.S. patent application Ser. No. 10/016,300 entitled “Lid Assembly For A Processing System To Facilitate Sequential Deposition Techniques,” filed on Dec. 12, 2001, which claims priority to U.S. Provisional Application Ser. No. 60/305,970 filed on Jul. 16, 2001, which are both incorporated by reference in their entirety to the extent not inconsistent with the present disclosure.  
      The gas distribution system  212 B includes a lid  621  and a process fluid injection assembly  630  to deliver reactive gases (i.e. precursor, reductant, oxidant), carrier gases, purge gases, cleaning gases and/or other fluids into the processing chamber. The fluid injection assembly  630  includes a gas manifold  634  mounting a plurality of control valves  632  (one is shown in  FIG. 6 ), and a baffle plate  636 . Each valve  632  is fluidly coupled to a separate trio of gas channels  671   a ,  671   b ,  673  (one trio is shown in  FIG. 6 ) of the gas manifold  634 . Gas channel  671   a  provides passage of gases through the gas manifold  634  to the valve  632 . Gas channel  671   b  delivers gases from the valve  632  through the gas manifold  634  and into a gas channel  673 . Channel  673  is fluidly coupled to a respective inlet passage  686  disposed through the lid  621 . Gases flowing through the inlet passages  686  flow into a plenum or region  688  defined between the lid  621  and the baffle plate  636  before entering the processing zone. The baffle plate  636  is utilized to prevent gases injected into the processing zone from blowing off gases adsorbed onto the surface of the substrate. The baffle plate  636  may include a mixing lip  684  to re-direct gases toward the center of the plenum  688  and into the process chamber.  
       FIG. 7  is a schematic cross-sectional view of another embodiment of a gas distribution system  212 C. The gas distribution system  212 C is shown and described in U.S. patent application Ser. No. 10/032,284 entitled “Gas Delivery Apparatus and Method for Atomic Layer Deposition,” filed on Dec. 21, 2001, which claims benefit of U.S. provisional Patent Application Ser. No. 60/346,086, entitled “Method and Apparatus for ALD Deposition,” filed Oct. 26, 2001, which are both incorporated by reference in their entirety to the extent not inconsistent with the present disclosure.  
      The gas distribution system  212 C comprises a chamber lid  732 . The chamber lid  732  includes an expanding channel  734  extending from a central portion of the chamber lid  732  and a bottom surface  760  extending from the expanding channel  734  to a peripheral portion of the chamber lid  732 . The bottom surface  760  is sized and shaped to substantially cover a substrate disposed on the substrate support. The expanding channel  734  has gas inlets  736 A,  736 B to provide gas flows from two similar valves. The gas inlets  736 A,  736 B are located adjacent the upper portion  737  of the expanding channel  734 . In other embodiments, one or more gas inlets may be located along the length of the expanding channel  734  between the upper portion  737  and a lower portion  735 . Each gas conduit  750 A,  750 B and gas inlet  736 A,  736 B may be positioned horizontally normal to the longitudinal axis  790  or may be angled downwardly at an angle +β or may be angled upwardly at an angle −β to the longitudinal axis  790 .  
      The expanding channel  734  comprises a channel which has an inner diameter which increases from an upper portion  737  to the lower portion  735  of the expanding channel  734  adjacent the bottom surface  760  of the chamber lid  732 . Whether a gas is provided toward the walls of the expanding channel  734  or directly downward towards the substrate, the velocity of the gas flow decreases as the gas flow travels through the expanding channel  734  due to the expansion of the gas. The reduction of the velocity of the gas flow helps reduce the likelihood the gas flow will blow off reactants adsorbed on the surface of the substrate.  
       FIG. 7A  is a top cross-sectional view of one embodiment of the expanding channel of the chamber lid of  FIG. 7 . Each gas conduit  750 A,  750 B may be positioned at an angle a from a center line of the gas conduit  750 A,  750 B and from a radius line from the center of the expanding channel  734 . Entry of a gas through the gas conduit  750 A,  750 B preferably positioned at an angle a (i.e., when α&gt;0°) causes the gas to flow in a circular direction as shown by arrows. Providing gas at an angle a as opposed to directly straight-on to the walls of the expanding channel (i.e. when α=0°) helps to provide a more laminar flow through the expanding channel  734  rather than a turbulent flow.  
      At least a portion of the bottom surface  760  of the chamber lid  732  may be tapered from the expanding channel  734  to a peripheral portion of the chamber lid  732  to help provide an improved velocity profile of a gas flow from the expanding channel  734  across the surface of the substrate (i.e., from the center of the substrate to the edge of the substrate). In one embodiment, the bottom surface  760  is tapered in the shape of a funnel. Not wishing to be bound by theory, in one aspect, the bottom surface  760  is downwardly sloping to help reduce the variation in the velocity of the gases as it travels between the bottom surface  760  of the chamber lid  732  and the substrate to help provide uniform exposure of the surface of the substrate to a reactant gas.  
       FIG. 8  is a schematic cross-section view of another embodiment of a gas distribution system  212 D. The gas distribution system  212 D is shown and described in U.S. patent application Ser. No. 10/118,664 (APPM/6422), which is incorporated by reference in its entirety to the extent not inconsistent with the present disclosure.  
      Gas distribution system  212  comprises a gas box  832 , a top shower plate  860  positioned below the gas box  832 , and a bottom shower plate  870  positioned below the top shower plate  860 . The gas distribution system  830  is adapted to provide gas flows to the substrate. The gas box  832  comprises a central gas channel  837  and a plurality of outer gas channels  843 . The central gas channel  837  provides one discrete path for the flow of one or more gases through the gas box  832  while the outer channels  843  provides another discrete path for the flow of one or more gases through the gas box  832 . The central gas channel  837  is coupled to a first gas source through a first valve. The central gas channel  837  has a first gas outlet  838  and is adapted to deliver a first gas from the first gas source  835  to a gas conduit  810 . The term “gas” as used herein is intended to mean a single gas or a gas mixture. The outer gas channels  843  are coupled to a second gas source through a second valve  842 . The outer gas channels  843  have second gas outlets  844  and are adapted to deliver a second gas from the second gas source  841  to the top shower plate  860 . Preferably, the second gas outlets  844  of the outer gas channels  843  are adapted to deliver the second gas proximate a central portion of the top shower plate.  
      The top shower plate  860  has a plurality of holes  862  to accommodate a gas flow therethrough from the outer gas channels  843  of the gas box  832  to the bottom shower plate  870 . The gas conduit  810  is disposed through an aperture  863  in the top shower plate  860  and is disposed on the bottom shower plate  870 .  
      The bottom shower plate  870  comprises a first piece  872  connected to a second piece  880 . The first piece  872  has a plurality of holes  874  to provide a flow of a gas therethrough. The second piece  880  comprises a plurality of columns  882  having column holes  883  formed therethrough and a plurality of grooves  884  having groove holes  885  formed therethrough. The top surface of the columns  882  are connected to the bottom surface of the first piece  872  so that the column holes  883  align with the holes  874  of the first piece  872 . Therefore, one discrete passageway is provided through the holes of the first piece  872  and through the column holes  883  of the columns  882  to deliver a gas flow from the top shower plate  860  to the substrate. An aperture  875  is formed through the first piece  872  and aligns with the grooves on the second piece  880 . Therefore, another discrete passageway is provided through the aperture  875  of the first piece  872  and through the grooves  884  and groove holes  885  of the second piece  880  to deliver a gas flow from the gas conduit  810 .  
       FIG. 9  is a schematic cross-sectional view of the top assembly  210  and the bottom assembly  240  of chamber  200  in a closed position. The top assembly  210  includes a gas distribution system  212 , such as the gas distribution systems described in reference to  FIGS. 5-8  or any other suitable gas distribution system. In one aspect, since the substrate support  242  is fixed, there is a smaller volume below the substrate support  242  since the volume does not have to take into account vertical movement of the substrate support  242 . In another aspect, the chamber provides easy access underneath the substrate support  242 . Therefore, the chamber may be cleaned without removing and realigning the substrate support  242 .  
      In one aspect, reactant gases flow from the gas distribution system  212  to a processing zone defined between the substrate support  242  of the bottom assembly  240  and the gas distribution assembly  212  of the top assembly  210 . In one embodiment, the spacing between the gas distribution assembly  212  and the substrate support  242  is about 0.75 inches or less to minimize the volume of the processing zone. The bottom purge gas flowing through the gap  284  between the substrate support  242  and the pumping ring  270  prevents the flow of process gases below the substrate support  242 . A smaller amount of reactant gases and/or purge gases are required to be provided to the chamber  200  through the gas distribution assembly  212  since reactant gases/purge gases from the gas distribution assembly  212  do not fill the volume below the substrate support  242 . For example, a smaller amount of reactant gases are required for a certain exposure of the substrate to the reactant gases. In addition, a smaller amount of purge gas is required to be provided through the gas distribution assembly  212  to remove the reactant gases from the chamber  200  since the purge gas does not need to remove reactant gases from the volume below the substrate support  242 . Therefore, the throughput of the chamber  200  is greater and waste may be minimized due to the smaller amount of gases used. For example, the time duration of pulses of a compound may be reduced. In addition, the time duration required to purge the chamber of a compound may be reduced.  
      The chamber  200  as shown and described in reference to  FIGS. 2-9  may be used to form any suitable material, such as aluminum oxide, other metal oxides, tantalum nitride, tantalum, tantalum silicon nitride, copper, copper aluminum, titanium nitride, titanium, titanium silicon nitride, tungsten nitride, tungsten, tungsten silicon nitride, organosilanes or organosiloxanes, other refractory metals, other refractory metal nitrides, other refractory metal compounds, other metals, other metal alloys, other high dielectric constant materials, other low dielectric constant materials, and other materials. The chamber  200  may be used to perform any suitable deposition technique, such as chemical vapor deposition, atomic layer deposition, cyclical layer deposition, and other suitable deposition techniques. Preferably, the chamber  200  is particularly advantageous in performing cyclical layer deposition. The term “cyclical layer deposition” as used herein refers to the sequential introduction of pulses of one or more compounds to deposit a thin layer of material on a substrate. Compounds can be reactants, reductants, precursors, catalysts, and mixtures thereof. Sequentially providing pulses of compounds may result in the formation of thin layers of material over a substrate structure. Each thin layer of material may be less than a monolayer, a monolayer, or more than a monolayer of material. The sequential introduction of pulses of compounds may be repeated to deposit a plurality of thin layers forming a conformal layer to a desired thickness. For simplicity and ease of description, however, a process for depositing an aluminum oxide film using chamber  200  is described in more detail below. In one embodiment, a method of depositing an aluminum oxide layer in chamber  200  over a substrate includes introducing an aluminum-containing compound, such as trimethyl aluminum, and an oxidizing compound through the gas distribution system  212 . The aluminum containing compound and the oxidizing compound may be introduced as a cycle of pulses through the gas distribution system  212 . A purge gas may be used to at least partially separate pulses of the aluminum containing compound and the oxidizing compound. In one embodiment, the pulses of the aluminum containing compound and the oxidizing compound are dosed into a continuous flow of a purge gas. In another embodiment, pulses of a purge gas are introduced through the gas distribution system  212 . The process may further include one or more annealing sequences and/or oxidizing sequences performed at various times during the aluminum oxide deposition cycle. For example, an annealing step may be performed after every deposition cycle or after any number of cycles are performed. As an example, an annealing step may be performed every third cycle, every four cycle, etc. or at a midpoint during the deposition process.. Other deposition processes of aluminum oxide are also possible.  
     EXAMPLES  
      The following examples will now reveal additional details and features concerning embodiments of the processing chamber. The following examples should not be construed to limit the scope of the invention unless expressly set forth in the claims.  
      Simulations were conducted of the flow of gases in regards to chambers, such as a chamber described in reference to  FIG. 2  and  FIG. 4 , having gas-flow diffusers of different heights. An uniform top flow of gases was provided to the substrate. Each chamber included a pumping ring having  24  apertures and a gas-flow diffuser extending between about 60% and about 70% around the perimeter of the substrate receiving surface  244 . In Example 1, the gas-flow diffuser had a tapered height with a maximum height of about 0.8 inches. In Example 2, the gas-flow diffuser had a tapered height with a maximum height of about 0.7 inches. The simulations estimated the velocity of gases 0.1 inch above a substrate positioned on a substrate support of the chambers. The simulations of Example 1 and Example 2 showed that the flow of gases were substantially uniform across the surface of the substrate.  
      While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. For example, many dimensions depend on the quantity of gas flow through the chamber.