Abstract:
Embodiments of the present invention generally relate to methods and apparatus for chemical vapor deposition (CVD) on a substrate, and, in particular, to a process chamber and components for use in metal organic chemical vapor deposition. The apparatus comprises a chamber body defining a process volume. A showerhead in a first plane defines a top portion of the process volume. A carrier plate extends across the process volume in a second plane forming an upper process volume between the showerhead and the susceptor plate. A transparent material in a third plane defines a bottom portion of the process volume forming a lower process volume between the carrier plate and the transparent material. A plurality of lamps forms one or more zones located below the transparent material. The apparatus provides uniform precursor flow and mixing while maintaining a uniform temperature over larger substrates thus yielding a corresponding increase in throughput.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments of the present invention generally relate to methods and apparatus for chemical vapor deposition (CVD) on a substrate, and, in particular, to a process chamber for use in chemical vapor deposition. 
         [0003]    2. Description of the Related Art 
         [0004]    Group III-V films are finding greater importance in the development and fabrication of a variety of semiconductor devices, such as short wavelength light emitting diodes (LEDs), laser diodes (LDs), and electronic devices including high power, high frequency, high temperature transistors and integrated circuits. For example, short wavelength (e.g., blue/green to ultraviolet) LEDs are fabricated using the Group Ill-nitride semiconducting material gallium nitride (GaN). It has been observed that short wavelength LEDs fabricated using GaN can provide significantly greater efficiencies and longer operating lifetimes than short wavelength LEDs fabricated using non-nitride semiconducting materials, comprising Group II-VI elements. 
         [0005]    One method that has been used for depositing Group III-nitrides, such as GaN, is metal organic chemical vapor deposition (MOCVD). This chemical vapor deposition method is generally performed in a reactor having a temperature controlled environment to assure the stability of a first precursor gas which contains at least one element from Group III, such as gallium (Ga). A second precursor gas, such as ammonia (NH 3 ), provides the nitrogen needed to form a Group III-nitride. The two precursor gases are injected into a processing zone within the reactor where they mix and move towards a heated substrate in the processing zone. A carrier gas may be used to assist in the transport of the precursor gases towards the substrate. The precursors react at the surface of the heated substrate to form a Group III-nitride layer, such as GaN, on the substrate surface. The quality of the film depends in part upon deposition uniformity which, in turn, depends upon uniform flow and mixing of the precursors across the substrate. 
         [0006]    As the demand for LEDs, LDs, transistors, and integrated circuits increases, the efficiency of depositing high quality Group-III nitride films takes on greater importance. Therefore, there is a need for an improved deposition apparatus and process that can provide uniform precursor mixing and consistent film quality over larger substrates and larger deposition areas. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention generally relates to methods and apparatus for chemical vapor deposition (CVD) on a substrate, and, in particular, to a process chamber and components for use in chemical vapor deposition. 
         [0008]    In one embodiment an apparatus for metal organic chemical vapor deposition on a substrate is provided. The process apparatus comprises a chamber body defining a process volume. A showerhead in a first plane defines a top portion of the process volume. A substrate carrier plate extends across the process volume in a second plane forming an upper process volume between the showerhead and the susceptor plate. A transparent material in a third plane defines a bottom portion of the process volume forming a lower process volume between the substrate carrier plate and the transparent material. A plurality of lamps forms one or more zones located below the transparent material. The plurality of lamps direct radiant heat toward the substrate carrier plate creating one or more radiant heat zones. 
         [0009]    In another embodiment a substrate processing apparatus for metal organic chemical vapor deposition is provided. The process apparatus comprises a chamber body defining a process volume. A showerhead in a first plane defines a top portion of the process volume. A substrate carrier plate extends across the process volume in a second plane below the first plane within the process volume. A light shield comprising an angled portion surrounds the periphery of the substrate carrier plate wherein the light shield directs radiant heat toward the substrate carrier plate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of 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. 
           [0011]      FIG. 1  is a cross-sectional view of a deposition chamber according to one embodiment of the invention; 
           [0012]      FIG. 2  is a partial cross-sectional view of the deposition chamber of  FIG. 1 ; 
           [0013]      FIG. 3  is a perspective view of a carrier plate according to one embodiment of the invention; 
           [0014]      FIG. 4A  is a perspective view of an upper surface of a susceptor plate according to one embodiment of the invention; 
           [0015]      FIG. 4B  is a perspective view of a lower surface of the susceptor plate according to one embodiment of the invention; 
           [0016]      FIG. 5A  is a perspective view of a susceptor support shaft according to one embodiment of the invention; 
           [0017]      FIG. 5B  is a perspective view of a susceptor support shaft according to another embodiment of the invention; 
           [0018]      FIG. 5C  is a perspective view of a susceptor support shaft according to another embodiment of the invention; 
           [0019]      FIG. 6  is a perspective view of a carrier lift shaft according to one embodiment of the invention; 
           [0020]      FIG. 7  is a schematic view of an exhaust process kit according to one embodiment of the invention; 
           [0021]      FIG. 8A  is a perspective view of an upper liner according to one embodiment of the invention; and 
           [0022]      FIG. 8B  is a perspective view of a lower liner according to one embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Embodiments of the present invention generally provide a method and apparatus that may be utilized for deposition of Group III-nitride films using MOCVD. Although discussed with reference to MOCVD, embodiments of the present invention are not limited to MOCVD.  FIG. 1  is a cross-sectional view of a deposition apparatus that may be used to practice the invention according to one embodiment of the invention.  FIG. 2  is a partial cross-sectional view of the deposition chamber of  FIG. 1 . Exemplary systems and chambers that may be adapted to practice the present invention are described in U.S. patent application Ser. No. 11/404,516, filed on Apr. 14, 2006, and Ser. No. 11/429,022, filed on May 5, 2006, both of which are incorporated by reference in their entireties. 
         [0024]    With reference to  FIG. 1  and  FIG. 2 , the apparatus  100  comprises a chamber  102 , a gas delivery system  125 , a remote plasma source  126 , and a vacuum system  112 . The chamber  102  includes a chamber body  103  that encloses a processing volume  108 . The chamber body  103  may comprise materials such as stainless steel or aluminum. A showerhead assembly  104  or gas distribution plate is disposed at one end of the processing volume  108 , and a carrier plate  114  is disposed at the other end of the processing volume  108 . Exemplary showerheads that may be adapted to practice the present invention are described in U.S. patent application Ser. No. 11/873,132, filed Oct. 16, 2007, titled MULTI-GAS STRAIGHT CHANNEL SHOWERHEAD, Ser. No. 11/873,141, filed Oct. 16, 2007, titled MULTI-GAS STRAIGHT CHANNEL SHOWERHEAD, and Ser. No. 11/873,170, filed Oct. 16, 2007, titled MULTI-GAS CONCENTRIC INJECTION SHOWERHEAD, all of which are incorporated by reference in their entireties. A transparent material  119 , configured to allow light to pass through for radiant heating of substrates  140 , is disposed at one end of a lower volume  110  and the carrier plate  114  is disposed at the other end of the lower volume  110 . The transparent material  119  may be dome shaped. The carrier plate  114  is shown in process position, but may be moved to a lower position where, for example, the substrates  140  may be loaded or unloaded. 
         [0025]      FIG. 3  is a perspective view of a carrier plate according to one embodiment of the invention. In one embodiment, the carrier plate  114  may include one or more recesses  116  within which one or more substrates  140  may be disposed during processing. In one embodiment, the carrier plate  114  is configured to carry six or more substrates  140 . In another embodiment, the carrier plate  114  is configured to carry eight substrates  140 . In another embodiment, the carrier plate  114  is configured to carry  18  substrates. In yet another embodiment, the carrier plate  114  is configured to carry  22  substrates. It is to be understood that more or less substrates  140  may be carried on the carrier plate  114 . Typical substrates  140  may include sapphire, silicon carbide (SiC), silicon, or gallium nitride (GaN). It is to be understood that other types of substrates  140 , such as glass substrates  140 , may be processed. Substrate  140  size may range from 50 mm-100 mm in diameter or larger. The carrier plate  114  size may range from 200 mm-750 mm. The carrier plate  114  may be formed from a variety of materials, including SiC or SiC-coated graphite. It is to be understood that substrates  140  of other sizes may be processed within the chamber  102  and according to the processes described herein. 
         [0026]    The carrier plate  114  may rotate about an axis during processing. In one embodiment, the carrier plate  114  may be rotated at about 2 RPM to about 100 RPM. In another embodiment, the carrier plate  114  may be rotated at about 30 RPM. Rotating the carrier plate  114  aids in providing uniform heating of the substrates  140  and uniform exposure of the processing gases to each substrate  140 . In one embodiment, the carrier plate  114  is supported by a carrier supporting device comprising a susceptor plate  115 . Exemplary substrate support structures that may be adapted to practice the present invention are described in U.S. patent application Ser. No. 11/552,474, filed Oct. 24, 2006, titled SUBSTRATE SUPPORT STRUCTURE WITH RAPID TEMPERATURE CHANGE, which IS incorporated by reference in its entirety. 
         [0027]      FIG. 4A  is a perspective view of an upper surface of a susceptor plate according to one embodiment of the invention.  FIG. 4B  is a perspective view of a lower surface of the susceptor plate according to one embodiment of the invention. The susceptor plate  115  has a disk form and is made of a graphite material coated with silicon carbide. The upper surface  156  of the susceptor plate  115  is formed with a circular recess  127 . The circular recess  127  acts as a support area for accommodating and supporting the carrier plate  114 . The susceptor plate  115  has three throughholes  158  for accommodating lift pins. The susceptor plate  115  is horizontally supported at three points from the underside by a susceptor support shaft  118  made of quartz disposed in the lower volume  110  of the chamber. The lower surface  159  of the susceptor plate has three holes  167  for accommodating the lift arms of the susceptor support shaft  118 . Although the susceptor plate  115  is described as having three holes  167 , any number of holes corresponding to the number of lift arms of the susceptor support shaft  118  may be used. 
         [0028]    The lift mechanism  150  will be discussed with respect to  FIGS. 5A-5C  and  FIG. 6 .  FIG. 5A  is a perspective view of the susceptor support shaft and  FIG. 6  is a perspective view of a carrier plate lift mechanism. The susceptor support shaft  118  comprises a central shaft  132  with three lift arms  134  extending radially from the central shaft  132 . Although the susceptor support shaft  118  is shown with three lift arms  134 , any number of lift arms greater than three may also be used, for example, the susceptor support shaft  118  may comprise six lift arms  192  as depicted in  FIG. 5B . In one embodiment depicted in  FIG. 5C  the lift arms are replace by a disk  195  with support posts  196  extending from the surface of the disk  195  to support the susceptor plate  115 . 
         [0029]    The carrier plate lift mechanism  150  comprises a vertically movable lift tube  152  arranged so as to surround the central shaft  132  of the susceptor support shaft  118 , a driving unit (not shown) for moving the lift tube  152  up and down, three lift arms  154  radially extending from the lift tube  152 , and lift pins  157  suspended from the bottom surface of the susceptor plate  115  by way of respective throughholes  158  formed so as to penetrate therethrough. When the driving unit is controlled so as to raise the lift tube  152  and lift arms  154  in such a configuration, the lift pins  157  are pushed up by the distal ends of the lift arms  154  whereby the carrier plate  114  rises. 
         [0030]    As shown in  FIG. 1 , radiant heating may be provided by a plurality of inner lamps  121 A, a plurality of central lamps  121 B, and a plurality of outer lamps  121 C disposed below the lower dome  119 . Reflectors  166  may be used to help control chamber  102  exposure to the radiant energy provided by the inner, central, and outer lamps  121 A,  121 B,  121 C. Additional zones of lamps may also be used for finer temperature control of the substrates  140 . In one embodiment, the reflectors  166  are coated with gold. In another embodiment, the reflectors  166  are coated with aluminum, rhodium, nickel, combinations thereof, or other highly reflective materials. In one embodiment, there are 72 lamps total comprising 24 lamps per zone at 2 kilowatts per lamp. In one embodiment, the lamps are air-cooled and the bases of the lamps are water cooled. 
         [0031]    The plurality of inner lamps, central lamps, and outer lamps  121 A,  121 B,  121 C may be arranged in concentric zones or other zones (not shown), and each zone may be separately powered allowing for the tuning of deposition rates and growth rates through temperature control. In one embodiment, one or more temperature sensors, such as pyrometers  122 A,  122 B,  122 C, may be disposed within the showerhead assembly  104  to measure substrate  140  and carrier plate  114  temperatures, and the temperature data may be sent to a controller (not shown) which can adjust power to each zone to maintain a predetermined temperature profile across the carrier plate  114 . In one embodiment, an inert gas is flown around the pyrometers  122 A,  122 B,  122 C into the processing volume  108  to prevent deposition and condensation from occurring on the pyrometers  122 A,  122 B,  122 C. The pyrometers  122 A,  122 B,  122 C can compensate automatically for changes in emissivity due to deposition on surfaces. Although three pyrometers  122 A,  122 B,  122 C are shown, it should be understood that any numbers of pyrometers may be used, for example, if additional zones of lamps are added it may be desirable to add additional pyrometers to monitor each additional zone. In another embodiment, the power to separate lamp zones may be adjusted to compensate for precursor flow or precursor concentration non-uniformity. For example, if the precursor concentration is lower in a carrier plate  114  region near an outer lamp zone, the power to the outer lamp zone may be adjusted to help compensate for the precursor depletion in this region. Advantages of using lamp heating over resistive heating include a smaller temperature range across the carrier plate  114  surface which improves product yield. The ability of lamps to quickly heat up and quickly cool down increases throughput and also helps create sharp film interfaces. 
         [0032]    Other metrology devices, such as a reflectance monitor  123 , thermocouples (not shown), or other temperature devices may also be coupled with the chamber  102 . The metrology devices may be used to measure various film properties, such as thickness, roughness, composition, temperature or other properties. These measurements may be used in an automated real-time feedback control loop to control process conditions such as deposition rate and the corresponding thickness. In one embodiment, the reflectance monitor  123  is coupled with the showerhead assembly  104  via a central conduit (not shown). Other aspects of the chamber metrology are described in U.S. patent application Ser. No. ______, filed Jan. 31, 2008, (attorney docket no. 011007) entitled CLOSED LOOP MOCVD DEPOSITION CONTROL, which is herein incorporated by reference in its entirety. 
         [0033]    The inner, central, and outer lamps  121 A,  121 B,  121 C may heat the substrates  140  to a temperature of about 400 degrees Celsius to about 1200 degrees Celsius. It is to be understood that the invention is not restricted to the use of arrays of inner, central, and outer lamps  121 A,  121 B, and  121 C. Any suitable heating source may be utilized to ensure that the proper temperature is adequately applied to the chamber  102  and substrates  140  therein. For example, in another embodiment, the heating source may comprise resistive heating elements (not shown) which are in thermal contact with the carrier plate  114 . 
         [0034]    With reference to  FIG. 2  and  FIG. 7 ,  FIG. 7  is a perspective view of an exhaust process kit according to one embodiment of the invention. In one embodiment, the process kit may comprise a light shield  117 , an exhaust ring  120 , and an exhaust cylinder  160 . As shown in  FIG. 2 , the light shield  117  may be disposed around the periphery of the carrier plate  114 . The light shield  117  absorbs energy that strays outside of the susceptor diameter from the inner lamps  121 A, the central lamps  121 B, and the outer lamps  121 C and helps redirect the energy toward the interior of the chamber  102 . The light shield  117  also blocks direct lamp radiant energy from interfering with metrology tools. In one embodiment, the light shield  117  generally comprises an annular ring with an inner edge and an outer edge. In one embodiment, the outer edge of the annular ring is angled upward. The light shield  117  generally comprises silicon carbide. The light shield  117  may also comprise alternative materials that absorb electromagnetic energy, such as ceramics. The light shield  117  may be coupled with the exhaust cylinder  160 , the exhaust ring  120  or other parts of the chamber body  103 . The light shield  117  generally does not contact the susceptor plate  115  or carrier plate  114 . 
         [0035]    In one embodiment, the exhaust ring  120  may be disposed around the periphery of the carrier plate  114  to help prevent deposition from occurring in the lower volume  110  and also help direct exhaust gases from the chamber  102  to exhaust ports  109 . In one embodiment, the exhaust ring  120  comprises silicon carbide. The exhaust ring  120  may also comprise alternative materials that absorb electromagnetic energy, such as ceramics. 
         [0036]    In one embodiment, the exhaust ring  120  is coupled with an exhaust cylinder  160 . In one embodiment, the exhaust cylinder  160  is perpendicular to the exhaust ring  120 . The exhaust cylinder  160  helps maintain uniform and equal radial flow from the center outward across the surface of the carrier plate  114  and controls the flow of gas out of process volume  108  and into the annular exhaust channel  105 . The exhaust cylinder  160  comprises an annular ring  161  having an inner sidewall  162  and an outer side wall  163  with throughholes or slots  165  extending through the sidewalls and positioned at equal intervals throughout the circumference of the ring  161 . In one embodiment, the exhaust cylinder  160  and the exhaust ring  120  comprise a unitary piece. In one embodiment the exhaust ring  120  and the exhaust cylinder  160  comprise separate pieces that may be coupled together using attachment techniques known in the art. With reference to  FIG. 2 , process gas flows downward from the showerhead assembly  104  toward the carrier plate  114  and travels radially outward over the light shield  117 , through the slots  165  in the exhaust cylinder  160  and into the annular exhaust channel  105  where it eventually exits the chamber  102  via exhaust port  109 . The slots in the exhaust cylinder  160  choke the flow of the process gas helping to achieve uniform radial flow over the entire susceptor plate  115 . In one embodiment, inert gas flows upward through a gap formed between the light shield  117  and the exhaust ring  120  to prevent process gas from entering the lower volume  110  of the chamber  102  and depositing on the lower dome  119 . Deposition on the lower dome  119  may affect temperature uniformity and in some cases may heat the lower dome  119  causing it to crack. 
         [0037]    A gas delivery system  125  may include multiple gas sources, or, depending on the process being run, some of the sources may be liquid sources rather than gases, in which case the gas delivery system may include a liquid injection system or other means (e.g., a bubbler) to vaporize the liquid. The vapor may then be mixed with a carrier gas prior to delivery to the chamber  102 . Different gases, such as precursor gases, carrier gases, purge gases, cleaning/etching gases or others may be supplied from the gas delivery system  125  to separate supply lines  131 ,  135  to the showerhead assembly  104 . The supply lines may include shut-off valves and mass flow controllers or other types of controllers to monitor and regulate or shut off the flow of gas in each line. In one embodiment, precursor gas concentration is estimated based on vapor pressure curves and temperature and pressure measured at the location of the gas source. In another embodiment, the gas delivery system  125  includes monitors located downstream of the gas sources which provide a direct measurement of precursor gas concentrations within the system. 
         [0038]    A conduit  129  may receive cleaning/etching gases from a remote plasma source  126 . The remote plasma source  126  may receive gases from the gas delivery system  125  via a supply line  124 , and a valve  130  may be disposed between the shower head assembly  104  and remote plasma source  126 . The valve  130  may be opened to allow a cleaning and/or etching gas or plasma to flow into the shower head assembly  104  via supply line  133  which may be adapted to function as a conduit for a plasma. In another embodiment, cleaning/etching gases may be delivered from the gas delivery system  125  for non-plasma cleaning and/or etching using alternate supply line configurations to shower head assembly  104 . In yet another embodiment, the plasma bypasses the shower head assembly  104  and flows directly into the processing volume  108  of the chamber  102  via a conduit (not shown) which traverses the shower head assembly  104 . 
         [0039]    The remote plasma source  126  may be a radio frequency or microwave plasma source adapted for chamber  102  cleaning and/or substrate  140  etching. Cleaning and/or etching gas may be supplied to the remote plasma source  126  via supply line  124  to produce plasma species which may be sent via conduit  129  and supply line  133  for dispersion through showerhead assembly  104  into chamber  102 . Gases for a cleaning application may include fluorine, chlorine or other reactive elements. 
         [0040]    In another embodiment, the gas delivery system  125  and remote plasma source  126  may be suitably adapted so that precursor gases may be supplied to the remote plasma source  126  to produce plasma species which may be sent through showerhead assembly  104  to deposit CVD layers, such as III-V films, for example, on substrates  140 . 
         [0041]    A purge gas (e.g., nitrogen) may be delivered into the chamber  102  from the showerhead assembly  104  and/or from inlet ports or tubes (not shown) disposed below the carrier plate  114  and near the bottom of the chamber body  103 . The purge gas enters the lower volume  110  of the chamber  102  and flows upwards past the carrier plate  114  and exhaust ring  120  and into multiple exhaust ports  109  which are disposed around an annular exhaust channel  105 . An exhaust conduit  106  connects the annular exhaust channel  105  to a vacuum system  112  which includes a vacuum pump (not shown). The chamber  102  pressure may be controlled using a valve system  107  which controls the rate at which the exhaust gases are drawn from the annular exhaust channel  105 . 
         [0042]    The showerhead assembly  104  is located near the carrier plate  114  during substrate  140  processing. In one embodiment, the distance from the showerhead assembly  104  to the carrier plate  114  during processing may range from about 4 mm to about 40 mm. 
         [0043]    During substrate processing, according to one embodiment of the invention, process gas flows from the showerhead assembly  104  towards the surface of the substrate  140 . The process gas may comprise one or more precursor gases as well as carrier gases and dopant gases which may be mixed with the precursor gases. The draw of the annular exhaust channel  105  may affect gas flow so that the process gas flows substantially tangential to the substrates  140  and may be uniformly distributed radially across the deposition surfaces of the substrate  140  deposition surfaces in a laminar flow. The processing volume  108  may be maintained at a pressure of about 760 Torr down to about 80 Torr. 
         [0044]    Reaction of process gas precursors at or near the surface of the substrate  140  may deposit various metal nitride layers upon the substrate  140 , including GaN, aluminum nitride (AlN), and indium nitride (InN). Multiple metals may also be utilized for the deposition of other compound films such as AlGaN and/or InGaN. Additionally, dopants, such as silicon (Si) or magnesium (Mg), may be added to the films. The films may be doped by adding small amounts of dopant gases during the deposition process. For silicon doping, silane (SiH 4 ) or disilane (Si 2 H 6 ) gases may be used, for example, and a dopant gas may include Bis(cyclopentadienyl) magnesium (Cp 2 Mg or (C 5 H 5 ) 2 Mg) for magnesium doping. 
         [0045]    In one embodiment, a fluorine or chlorine based plasma may be used for etching or cleaning. In other embodiments, halogen gases, such as Cl 2 , Br, and I 2 , or halides, such as HCl, HBr, and HI, may be used for non-plasma etching. 
         [0046]    In one embodiment, a carrier gas, which may comprise nitrogen gas (N 2 ), hydrogen gas (H 2 ), argon (Ar) gas, another inert gas, or combinations thereof may be mixed with the first and second precursor gases prior to delivery to the showerhead assembly  104 . 
         [0047]    In one embodiment, the first precursor gas may comprise a Group III precursor, and second precursor gas may comprise a Group V precursor. The Group III precursor may be a metal organic (MO) precursor such as trimethyl gallium (“TMG”), triethyl gallium (TEG), trimethyl aluminum (“TMAI”), and/or trimethyl indium (“TMI”), but other suitable MO precursors may also be used. The Group V precursor may be a nitrogen precursor, such as ammonia (NH 3 ). 
         [0048]      FIG. 8A  is a perspective view of an upper liner according to one embodiment of the invention.  FIG. 8B  is a perspective view of a lower liner according to one embodiment of the invention. In one embodiment, the process chamber  102  further comprises an upper process liner  170  and a lower process liner  180  which help protect the chamber body  103  from etching by process gases. In one embodiment, the upper process liner  170  and the lower process liner  180  comprise a unitary body. In another embodiment, the upper process liner  170  and the lower process liner  180  comprise separate pieces. The lower process liner  180  is disposed in the lower volume  110  of the process chamber  102  and upper process liner  170  is disposed adjacent to the showerhead assembly  104 . In one embodiment, the upper process liner  170  rests on the lower process liner  180 . In one embodiment, lower liner  170  has a slit valve port  802  and an exhaust port  804  opening which may form a portion of exhaust port  109 . The upper process liner  170  has an exhaust annulus  806  which may form a portion of annular exhaust channel  105 . The liners may comprise thermally insulating material such as opaque quartz, sapphire, PBN material, ceramic, derivatives thereof or combinations thereof. 
         [0049]    An improved deposition apparatus and process that provides uniform precursor flow and mixing while maintaining a uniform temperature over larger substrates and larger deposition areas has been provided. The uniform mixing and heating over larger substrates and/or multiple substrates and larger deposition areas is desirable in order to increase yield and throughput. Further uniform heating and mixing are important factors since they directly affect the cost to produce an electronic device and, thus, a device manufacturer&#39;s competitiveness in the market place. 
         [0050]    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.