Patent Publication Number: US-2005121145-A1

Title: Thermal processing system with cross flow injection system with rotatable injectors

Description:
CROSS REFERENCE TO RELATED APPLICATION  
      This application claims the benefit of and priority to U.S. Provisional Patent Application No. 60/506,354 filed Sep. 25, 2003, the disclosure of which is hereby incorporated by reference in its entirety, and is related to PCT application Serial No. PCT/US03/21575 entitled Thermal Processing System and Configurable Vertical Chamber, which claims priority to U.S. Provisional patent application Ser. Nos. 60/396,536 and 60/428,526, the disclosures of all of which are hereby incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD  
      The present invention relates generally to systems and methods for heat-treating objects, such as substrates. More specifically, the present invention relates to an apparatus and method for heat treating, annealing, and depositing layers of material on or removing layers of material from a semiconductor wafer or substrate.  
     BACKGROUND  
      Thermal processing apparatuses are commonly used in the manufacture of integrated circuits (ICs) or semiconductor devices from semiconductor substrates or wafers. Thermal processing of semiconductor wafers include, for example, heat treating, annealing, diffusion or driving of dopant material, deposition or growth of layers of material, and etching or removal of material from the substrate. These processes often call for the wafer to be heated to a temperature as high as 1300° C. and as low as 300° C. before and during the process, and that one or more fluids, such as a process gas or reactant, be delivered to the wafer. Moreover, these processes typically require that the wafer be maintained at a uniform temperature throughout the process, despite variations in the temperature of the process gas or the rate at which it is introduced into the process chamber.  
      A conventional thermal processing apparatus typically consists of a voluminous process chamber positioned in or surrounded by a furnace. Substrates to be thermally processed are sealed in the process chamber, which is then heated by the furnace to a desired temperature at which the processing is performed. For many processes, such as Chemical Vapor Deposition (CVD), the sealed process chamber is first evacuated, and once the process chamber has reached the desired temperature a reactive or process gases are introduced to form or deposit reactant species on the substrates.  
      In the past, thermal processing apparatus typically and in particular vertical thermal processing apparatuses, required guard heaters disposed adjacent to sidewalls of the process chamber above and below the process zone in which product wafers were processed. This arrangement is undesirable since it entails a larger chamber volume that must be pumped down, filled with process gas or vapor, and backfilled or purged, resulting in increased processing time. Moreover, this configuration takes up a tremendous amount of space and power due to a poor view factor of the wafers from the heaters.  
      Other problems with conventional thermal processing apparatuses include the considerable time required both before processing to ramp up the temperature of the process chamber and the wafer to be treated, and the time required after processing to ramp down the temperature. Furthermore, additional time is often required to ensure the temperature of the process chamber has stabilized uniformly at the desired temperature before processing can begin. While the actual time required for processing of the wafers may be half hour or less, pre- and post-processing times typically take 1 to 3 hours or longer. Thus, the time required to quickly ramp up and/or down the temperature of the process chamber to a uniform temperature significantly limits the throughput of the conventional thermal processing apparatus.  
      A fundamental reason for the relatively long ramp up and ramp down times is the thermal mass of the process chamber and/or furnace in conventional thermal processing apparatuses, which must be heated or cooled prior to effectively heating or cooling the wafer.  
      A common approach to minimizing or offsetting this limitation on throughput of conventional thermal processing apparatus has been to increase the number of wafers capable of being processed in a single cycle or run. Simultaneous processing of a large number of wafers helps to maximize the effective throughput of the apparatus by reducing the effective processing time on a per wafer basis. However, this approach also increases the magnitude of the risk should something go wrong during processing. That is a larger number of wafers could be destroyed or damaged by a single failure, for example, if there was an equipment or process failure during a single processing cycle. This is particularly a concern with larger wafer sizes and more complex integrated circuits where a single wafer could be valued at from $1,000 to $10,000 depending on the stage of processing.  
      Another problem with this solution is that increasing the size of the process chamber to accommodate a larger number of wafers increases the thermal mass effects of the process chamber, thereby reducing the rate at which the wafer can be heated or cooled. Moreover, larger process chambers processing larger batches of wafers leads to or compounds a first-in-last-out syndrome in which the first wafers loaded into the chamber are also the last wafers removed, resulting in these wafers being exposed to elevated temperatures for longer periods and reducing uniformity across the batch of wafers.  
      Another problem with the above approach is that systems and apparatuses used for many of the processes before and after thermal processing are not amenable to simultaneous processing of large numbers of wafers. Thus, thermal processing of large batches or large numbers wafers, while increasing the throughput of the thermal processing apparatus, can do little to improve the overall throughput of the semiconductor fabrication facility and may actually reduce it by requiring wafers to accumulate ahead of the thermal processing apparatus or causing wafers to bottleneck at other systems and apparatuses downstream therefrom.  
      An alternative to the conventional thermal processing apparatus described above, are rapid thermal processing (RTP) systems that have been developed for rapidly thermal processing of wafers. Conventional RTP systems generally use high intensity lamps to selectively heat a single wafer or small number of wafers within a small, transparent, usually quartz, process chamber. RTP systems minimize or eliminate the thermal mass effects of the process chamber, and since the lamps have very low thermal mass, the wafer can be heated and cooled rapidly by instantly turning the lamps on or off.  
      Unfortunately, conventional RTP systems have significant shortcomings including the placement of the lamps, which in the past were arranged in zones or banks each consisting of a number of lamps adjacent to sidewalls of the process chamber. This configuration is problematic because it takes up a tremendous amount of space and power in order to be effective due to their poor view factor, all of which are at a premium in the latest generation of semiconductor processing equipment.  
      Another problem with conventional RTP systems is their inability to provide uniform temperature distribution across multiple wafers within a single batch of wafers and even across a single wafer. There are several reasons for this non-uniform temperature distribution including (i) a poor view factor of one or more of the wafers by one or more of the lamps, and (ii) variation in output power from the lamps.  
      Moreover, failure or variation in the output of a single lamp can adversely affect the temperature distribution across the wafer. Because of this in most lamp-based systems, the wafer or wafers are rotated to ensure that the temperature non-uniformity due to the variation in lamp output is not transferred to the wafer during processing. However, the moving parts required to rotate the wafer, particularly the rotating feedthrough into the process chamber, adds to the cost and complexity of the system, and reduces the overall reliability thereof.  
      Yet another troublesome area for RTP systems is in maintaining uniform temperature distribution across the outer edges and the center of the wafer. Most conventional RTP systems have no adequate means to adjust for this type of temperature non-uniformity. As a result, transient temperature fluctuations occur across the surface of the wafer that can cause the formation of slip dislocations in the wafer at high temperatures, unless a black body susceptor is used that is larger in diameter than the wafer.  
      Conventional lamp-based RTP systems have other drawbacks. For example, there are no adequate means for providing uniform power distribution and temperature uniformity during transient periods, such as when the lamps are powered on and off, unless phase angle control is used which produces electrical noise. Repeatability of performance is also usually a drawback of lamp-based systems, since each lamp tends to perform differently as it ages. Replacing lamps can also be costly and time consuming, especially when one considers that a given lamp system may have upwards of 180 lamps. The power requirement may also be costly, since the lamps may have a peak power consumption of about 250 kWatts.  
      Accordingly, there is a need for an apparatus and method for quickly and uniformly heating a batch of one or more substrates to a desired temperature across the surface of each substrate in the batch of during thermal processing.  
     SUMMARY OF THE INVENTION  
      The present invention provides a solution to these and other problems, and offers other advantages over the prior art.  
      The present invention provides an apparatus and method for isothermally heating work pieces, such as semiconductor substrates or wafers, for performing processes such as annealing, diffusion or driving of dopant material, deposition or growth of layers of material, and etching or removal of material from the wafer.  
      A thermal processing apparatus is provided for processing substrates held in a carrier at high or elevated temperatures. The apparatus includes a process chamber having a top wall, a side wall and a bottom wall, and a heating source having a number of heating elements proximal to the top wall, the side wall and the bottom wall of the process chamber to provide an isothermal environment in a process zone in which the carrier is positioned to thermally process the substrates. According to one aspect, the dimensions of the process chamber are selected to enclose a volume substantially no larger than a volume necessary to accommodate the carrier, and the process zone extends substantially throughout the process chamber. Preferably, the process chamber has dimensions selected to enclose a volume substantially no larger than 125% of that necessary to accommodate the carrier. More preferably, the apparatus further includes a pumping system to evacuate the process chamber prior to processing pressure and a purge system to backfill the process chamber after processing is complete, and the dimensions of the process chamber are selected to provide both a rapid evacuation and a rapid backfilling of the process chamber.  
      According to another aspect of the invention, the bottom wall of the process chamber includes a movable pedestal having at least one heating element therein, and the movable pedestal is adapted to be lowered and raised to enable the carrier with the substrates to be inserted into and removed from the process chamber. In one embodiment, the apparatus further includes a removable thermal shield adapted to be inserted between heating element in the pedestal and the substrates held the carrier. The thermal shield is adapted to reflect thermal energy from the heating element in the pedestal back to the pedestal, and to shield the substrates on the carrier from thermal energy from the heating element in the pedestal. In one version of this embodiment, the apparatus further includes a shutter adapted to be moved into place above the carrier to isolate the process chamber when the pedestal is in a lowered position. Where the apparatus includes a pumping system to evacuate the process chamber, and the shutter can be adapted to seal with the process chamber, thereby enabling the pumping system to evacuate the process chamber when the pedestal is in the lowered position.  
      In yet another embodiment, the apparatus further includes a magnetically coupled repositioning system that repositions the carrier during thermal processing of the substrates. Preferably, the mechanical energy used to reposition the carrier is magnetically coupled through the pedestal to the carrier without use of a movable feedthrough into the process chamber, and substantially without moving the heating element in the pedestal. More preferably, the magnetically coupled repositioning system is a magnetically coupled rotation system that rotates the carrier within the process zone during thermal processing of the substrates.  
      According to yet another aspect of the invention, the apparatus further includes a liner separating the carrier from the top wall and the side wall of the process chamber, and a distributive or cross-flow injection system to direct flow of a fluid across surfaces of each of the substrates held in the carrier. The cross-flow injection system generally includes a cross-flow injector having a number of injection ports positioned relative to substrates held in the carrier, and through which the fluid is introduced on one side of the number of substrates. A number of exhaust ports in the liner positioned relative to the substrates held in the carrier cause the fluid to flow across the surfaces of the substrates. Fluids introduced by the cross-flow injection system can include process gas or vapor, and inert purge gases or vapor used for purging or backfilling the chamber or for cooling the substrates therein.  
      In another aspect, the apparatus of the present invention includes an injection system which provides for selectable injection of gases to the process chamber. In general, the injection system of the present invention comprises one or more elongated injection tubes having a plurality of injection ports or orifices distributed in the tubes for directing flow of reactant and other gases across the surface of each substrate. The elongated injection tubes are rotatable about an axis in 360 degrees.  
      In another embodiment, the apparatus of the present invention comprises a process chamber providing a process region for a plurality of substrates held in a carrier, a cross-flow liner enclosing the carrier, and a cross-flow injection system disposed between the carrier and the cross-flow liner to direct flow of one or more gases across the surface of each substrate. The cross-flow injection system comprising a plurality of injection ports rotatable about an axis. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and various other features and advantages of the present invention will be apparent upon reading of the following detailed description in conjunction with the accompanying drawings and the appended claims provided below, where:  
       FIG. 1  is a cross-sectional view of a thermal processing apparatus having a pedestal heater for providing an isothermal control volume according to an embodiment of the present invention, employing conventional up-flow configuration;  
       FIG. 2  is a perspective view of an alternative embodiment a base-plate useful in the thermal processing apparatus shown in  FIG. 1 ;  
       FIG. 3  is a cross-sectional view of a portion of a thermal processing apparatus having a pedestal heater and a thermal shield according to an embodiment of the present invention;  
       FIG. 4  is a diagrammatic illustration of the pedestal heater and thermal shield of  FIG. 3  according to an embodiment of the present invention;  
       FIG. 5  is a diagrammatic illustration of an embodiment of the thermal shield having a top layer of material with a high absorptivity and a lower layer of material with a high reflectivity according to present invention;  
       FIG. 6  is a diagrammatic illustration of another embodiment of the thermal shield having a cooling channel according to present invention;  
       FIG. 7  is a perspective view of an embodiment of a thermal shield and an actuator according to present invention;  
       FIG. 8  is a cross-sectional view of a portion of a thermal processing apparatus having a shutter according to an embodiment of the present invention;  
       FIG. 9  is a cross-sectional view of a process chamber having a pedestal heater and a magnetically coupled wafer rotation system according to an embodiment of the present invention;  
       FIG. 10  is a cross-sectional view of a thermal processing apparatus having a cross-flow injector system according to an embodiment of the present invention;  
       FIG. 11  is a cross-sectional side view of a portion of the thermal processing apparatus of  FIG. 10  showing positions of injector orifices in relation to the liner and of exhaust slots in relation to the wafers according to an embodiment of the present invention;  
       FIG. 12  is a plan view of a portion of the thermal processing apparatus of  FIG. 10  taken along the line A-A of  FIG. 10  showing gas flow from orifices of a primary and a secondary injector across a wafer and to an exhaust port according to an embodiment of the present invention;  
       FIG. 13  is a plan view of a portion of the thermal processing apparatus of  FIG. 10  taken along the line A-A of  FIG. 10  showing gas flow from orifices of a primary and a secondary injector across a wafer and to an exhaust port according to another embodiment of the present invention;  
       FIG. 14  is a plan view of a portion of the thermal processing apparatus of  FIG. 10  taken along the line A-A of  FIG. 10  showing gas flow from orifices of a primary and a secondary injector across a wafer and to an exhaust port according to yet another embodiment of the present invention;  
       FIG. 15  is a plan view of a portion of the thermal processing apparatus of  FIG. 10  taken along the line A-A of  FIG. 10  showing gas flow from orifices of a primary and a secondary injector across a wafer and to an exhaust port according to still another embodiment of the present invention;  
       FIG. 16  is a cross-sectional view of a thermal processing apparatus having an alternative up-flow injector system according to an embodiment of the present invention;  
       FIG. 17  is a cross-sectional view of a thermal processing apparatus having an alternative down-flow injector system according to an embodiment of the present invention;  
       FIG. 18  is flowchart showing an embodiment of a process for thermally processing a batch of wafers according to an embodiment of the present invention whereby each wafer of the batch of wafers is quickly and uniformly heated to the desired temperature; and  
       FIG. 19  is flowchart showing another embodiment of a process for thermally processing a batch of wafers according to an embodiment of the present invention whereby each wafer of the batch of wafers is quickly and uniformly heated to the desired temperature.  
       FIG. 20  is a cross-sectional view of a thermal processing apparatus including an injection system according to one embodiment of the present invention.  
       FIG. 21  shows an elongated tube having a plurality of injection ports in accordance with one embodiment of the present invention.  
       FIG. 22  is a partial cross-sectional side view of a thermal processing apparatus showing connection of the injection system with a cross-flow liner and a base plate in accordance with one embodiment of the present invention.  
       FIG. 23  is a partial cross-sectional top view of a thermal processing apparatus showing connection of the injection system with a cross-flow liner and a base plate in accordance with one embodiment of the present invention.  
       FIG. 24  is a partial plan view of a liner top plate showing openings having notches.  
       FIG. 25  is an external view of a cross-flow stepped liner showing a longitudinal bulging section according to one embodiment of the present invention.  
       FIG. 26  is an external view of a cross-flow stepped liner showing a plurality of exhaust slots in the liner according to one embodiment of the present invention.  
       FIG. 27  is a plan view of an injection system with a cross-flow liner having a bulging section showing gas flow from orifices that impinges the liner inner wall prior to flowing across a wafer and exiting an exhaust slot according to one embodiment of the present invention.  
       FIG. 28  is a plan view of an injection system with a cross-flow liner having a bulging section showing gas flow from orifices that impinges each other prior to flowing across a wafer and exiting an exhaust slot according to one embodiment of the present invention.  
       FIG. 29  is a plan view of an injection system with a cross-flow liner having a bulging section showing gas flow from orifices directing to the center of a wafer and exiting an exhaust slot according to one embodiment of the present invention.  
       FIG. 30  is CFD demonstration for a thermal processing apparatus including an injection system having injection ports facing the center of a substrate in accordance with one embodiment of the present invention for deposition of silicon nitride.  
       FIG. 31  is CFD demonstration for a thermal processing apparatus including an injection system having injection ports facing each other in accordance with one embodiment of the present invention for deposition of silicon nitride.  
       FIG. 32  is CFD demonstration for a thermal processing apparatus including an injection system having injection ports facing the liner inner wall in accordance with one embodiment of the present invention for deposition of aluminum oxide. 
    
    
     DETAILED DESCRIPTION  
      The present invention is directed to an apparatus and method for processing a relatively small number or mini-batch of one or more work pieces, such as semiconductor substrates or wafers, held in a carrier, such as a cassette or boat, that provides reduced processing cycle times and improved process uniformity.  
      As used herein the term “mini-batch” means a number of wafers less than the hundreds of wafers found in the typical batch systems, and preferably in the range of from one to about fifty-three semiconductor wafers or wafers, of which from one to fifty are product wafers and the remainder are non-product wafers used for monitoring purposes and as baffle wafers.  
      By thermal processing it is meant processes that in which the work piece or wafer is heated to a desired temperature which is typically in the range of about 350° C. to 1300° C. Thermal processing of semiconductor wafers can include, for example, heat treating, annealing, diffusion or driving of dopant material, deposition or growth of layers of material, such as chemical vapor deposition or CVD, and etching or removal of material from the wafers.  
      A thermal processing apparatus according to an embodiment will now be described with reference to  FIG. 1 . For purposes of clarity, many of the details of thermal processing apparatuses that are widely known and are widely known to a person of skill in the art have been omitted. Such detail is described in more detail in, for example, commonly assigned U.S. Pat. No. 4,770,590, which is incorporated herein by reference.  
       FIG. 1  is a cross-sectional view of an embodiment of a thermal processing apparatus for thermally processing a batch of semiconductor wafers. As shown, the thermal processing apparatus  100 , generally includes a vessel  101  that encloses a volume to form a process chamber  102  having a support  104  adapted for receiving a carrier or boat  106  with a batch of wafers  108  held therein, and heat source or furnace  110  having a number of heating elements  112 - 1 ,  112 - 2  and  112 - 3  (referred to collectively hereinafter as heating elements  112 ) for raising a temperature of the wafers to the desired temperature for thermal processing. The thermal processing apparatus  100  further includes one or more optical or electrical temperature sensing elements, such as a resistance temperature device (RTD) or thermal couple (T/C), for monitoring the temperature within the process chamber  102  and/or controlling operation of the heating elements  112 . In the embodiment shown the temperature sensing element is a profile T/C  114  that has multiple independent temperature sensing nodes or points (not shown) for detecting the temperature at multiple locations within the process chamber  102 . The thermal processing apparatus  100  can also include one or more injectors  116  (only one of which is shown) for introducing a fluid, such as a gas or vapor, into the process chamber  102  for processing and/or cooling the wafers  108 , and one or more purge ports or vents  118  (only one of which is shown) for introducing a gas to purge the process chamber and/or to cool the wafers. A liner  120  increases the concentration of processing gas or vapor near the wafers  108  in a region or process zone  128  in which the wafers are processed, and reduces contamination of the wafers from flaking or peeling of deposits that can form on interior surfaces of the process chamber  102 . Processing gas or vapor exits the process zone through exhaust ports or slots  121  in the chamber liner  120 .  
      Generally, the vessel  101  is sealed by a seal, such as an o-ring  122 , to a platform or base-plate  124  to form the process chamber  102 , which completely encloses the wafers  108  during thermal processing. The dimensions of the process chamber  102  and the base-plate  124  are selected to provide a rapid evacuation, rapid heating and a rapid backfilling of the process chamber. Advantageously, the vessel  101  and the base-plate  124  are sized to provide a process chamber  102  having dimensions selected to enclose a volume substantially no larger than necessary to accommodate the carrier  106  with the wafers  108  held therein. Preferably, the vessel  101  and the base-plate  124  are sized to provide a process chamber  102  having dimensions of from about 125 to about 150% of that necessary to accommodate the carrier  106  with the wafers  108  held therein, and more preferably, the process chamber has dimensions no larger than about 125% of that necessary to accommodate the carrier and the wafers in order to minimize the chamber volume which aids in pump down and back-fill time required.  
      Openings for the injectors  116 , T/Cs  114  and vents  118  are sealed using seals such as o-rings, VCR®, or CF® fittings Gases or vapor released or introduced during processing are evacuated through a foreline or exhaust port  126  formed in a wall of the process chamber  102  (not shown) or in a plenum  127  of the base-plate  124 , as shown in  FIG. 1 . The process chamber  102  can be maintained at atmospheric pressure during thermal processing or evacuated to a vacuum as low as 5 millitorr through a pumping system (not shown) including one or more roughing pumps, blowers, hi-vacuum pumps, and roughing, throttle and foreline valves.  
      In another embodiment, shown in  FIG. 2 , the base-plate  124  further includes a substantially annular flow channel  129  adapted to receive and support an injector  116  including a ring  131  from which depend a number of vertical injector tube or injectors  116 A. The injectors  116 A can be sized and shaped to provide an up-flow, down flow or cross-flow flow pattern, as described below. The ring  131  and injectors  116 A are located so as to inject the gas into the process chamber  102  between the boat  106  and the vessel  101 . In addition, the injectors  116 A are spaced apart around the ring  131  to uniformly introduce process gas or vapor into the process chamber  102 , and may, if desired, be used during purging or backfilling to introduce a purge gas into the process chamber. The base-plate  124  is sized in a short cylindrical form with an outwardly extending upper flange  133 , a sidewall  135 , and an inwardly extending base  137 . The upper flange  133  is adapted to receive and support the vessel  101 , and contains an o-ring  122  to seal the vessel to the upper flange. The base  137  is adapted to receive and support the liner  120  outside of where the ring  131  of injectors  116  is supported.  
      Additionally, the base-plate  124  shown in  FIG. 2  incorporates various ports including backfill/purge gas inlet ports  139 ,  143 , cooling ports  145 , 147 , provided to circulate cooling fluid in the base-plate  124 , and a pressure monitoring port  149  for monitoring pressure within the process chamber  102 . Process gas inlet ports  151 ,  161 , introduce a gas from a supply (not shown) to the injectors  116 . The backfill/purge ports  139 , 143 , are provided at the sidewall  135  of the base-plate  124  principally to introduce a gas from a vent/purge gas supply (not shown) to the vents  118 . A mass flow controller (not shown) or any other suitable flow controller is placed in line between the gas supplies and the ports  139 ,  143 ,  151  and  161  to control the gas flow into the process chamber  102 .  
      The vessel  101  and liner  120  can be made of any metal, ceramic, crystalline or glass material that is capable of withstanding the thermal and mechanical stresses of high temperature and high vacuum operation, and which is resistant to erosion from gases and vapors used or released during processing. Preferably, the vessel  101  and liner  120  are made from an opaque, translucent or transparent quartz glass having a sufficient thickness to withstand the mechanical stresses and that resists deposition of process byproducts, thereby reducing potential contamination of the processing environment. More preferably, the vessel  101  and liner  120  are made from quartz that reduces or eliminates the conduction of heat away from the region or process zone  128  in which the wafers  108  are processed.  
      The batch of wafers  108  is introduced into the thermal processing apparatus  100  through a load lock or loadport (not shown) and then into the process chamber  102  through an access or opening in the process chamber or base-plate  124  capable of forming a gas tight seal therewith. In the configuration shown in  FIG. 1 , the process chamber  102  is a vertical reactor and the access utilizes a movable pedestal  130  that is raised during processing to seal with a seal, such as an o-ring  132  on the base-plate  124 , and lowered to enable an operator or an automated handling system, such as a boat handling unit (BHU) (not shown), to position the carrier or boat  106  on the support  104  affixed to the pedestal.  
      The heating elements  112  include elements positioned proximal to a top  134  (elements  112 - 3 ), side  136  (elements  112 - 2 ) and bottom  138  (elements  112 - 1 ) of the process chamber  102 . Advantageously, the heating elements  112  surround the wafers to achieve a good view factor of the wafers and thereby provide an isothermal control volume or process zone  128  in the process chamber in which the wafers  108  are processed. The heating elements  112 - 1  proximal to the bottom  138  of the process chamber  102  can be disposed in or on the pedestal  130 . If desired, additional heating elements may be disposed in or on the base plate  124  to supplement heat from the heating elements  112 - 1 .  
      In the embodiment shown in  FIG. 1  the heating elements  112 - 1  proximal to the bottom of the process chamber preferably are recessed in the movable pedestal  130 . The pedestal  130  is made from a thermally and electrically insulating material or insulating block  140  having an electric, resistive heating elements  112 - 1  embedded therein or affixed thereto. The pedestal  130  further includes one or more feedback sensors or T/Cs  141  used to control the heating elements  112 - 1 . In the configuration shown, the T/Cs  141  are embedded in the center of the insulating block  140 .  
      The side heating elements  112 - 2  and the top heating elements  112 - 3  may be disposed in or on an insulating block  110  about the vessel  101 . Preferably the side heating elements  112 - 2  and the top heating elements  112 - 3  are recessed in the insulating block  110 .  
      The heating elements  112  and the insulating blocks  110  and  140  may be configured in any of a variety of ways and may be made in any of a variety of ways and with any of a variety of materials.  
      Preferably, to attain desired processing temperatures of up to 1150° C. the heating elements  112 - 1  proximal to the bottom  138  of the process chamber  102  have a maximum power output of from about 0.1 kW to about 10 kW with a maximum process temperature of at least 1150° C. More preferably, these bottom heating elements  112 - 1  have a power output of at least about 3.8 kW with a maximum process temperature of at least 950° C. In one embodiment, the side heating elements  112 - 2  are functionally divided into multiple zones, including a lower zone nearest the pedestal  130  and upper zone, each of which are capable of being operated independently at different power levels and duty cycles from each other and from the top heating elements  112 - 3  and bottom heating elements  112 - 1 .  
      The heating elements  112  are controlled in any suitable manner, either by using a control technique of a type well known in the art.  
      Contamination from the insulating block  140  and bottom heating elements  112 - 1  is reduced if not eliminated by housing the heating element and insulation block in an inverted quartz crucible  142 , which serves as a barrier between the heating element and insulation block and the process chamber  102 . The crucible  142  is also sealed against the loadport and BHU environment to further reduce or eliminate contamination of the processing environment. Generally, the interior of the crucible  142  is at standard atmospheric pressure, so that the crucible  142  should be strong enough to withstand a pressure differential between the process chamber  102  and the pedestal  130  across the crucible  142  of as much as  1  atmosphere.  
      While the wafers  108  are being loaded or unloaded, that is while the pedestal  130  is in the lowered position ( FIG. 3 ), the bottom heating elements  112 - 1  are powered to maintain an idle temperature lower than the desired processing temperature. For example, for a process having a desired processing temperature for the bottom heating elements of 950° C., the idle temperature can be from 50-150°. The idle temperature can be set higher for certain processes, such as those having a higher desired processing temperature and/or higher desired ramp up rate, or to reduce thermal cycling effects on the bottom heating elements  112 - 1 , thereby extending element life.  
      In order to further reduce preprocessing time, that is the time required to prepare the thermal processing apparatus  100  for processing, the bottom heating elements  112 - 1  can be ramped to at or below the desired process temperature during the push or load, that is while the pedestal  130  with a boat  106  of wafers  108  positioned thereon is being raised. However, to minimize thermal stresses on the wafers  108  and components of the thermal processing apparatus  100  it is preferred to have the bottom heating elements  112 - 1  reach the desired process temperature at the same time as the heating elements  112 - 3  and  112 - 2  located proximal to respectively the top  134  and side  136  of the process chamber  102 . Thus, for some processes, such as those requiring higher desired process temperatures, the temperature of the bottom heating elements  112 - 1  can begin being ramped up before the pedestal  130  begins being raised, while the last of the wafers  108  in a batch are being loaded.  
      Similarly, it will be appreciated that after processing and during the pull or unload cycle, that is while the pedestal  128  is being lowered, power to the bottom heating elements  112 - 1  can be reduce or removed completely to begin ramping down the pedestal  130  to the idle temperature, in preparation for cooling of the wafers  108  and unloading by the BHU.  
      To assist in cooling the pedestal  130  to a pull temperature prior to the pull or unload cycle, a purge line for air or an inert purge gas, such as nitrogen, is installed through the insulating block  140 . Preferably, nitrogen is injected through a passage  144  through the center of the insulating block  140  and allowed to flow out between the top of the insulating block  140  and the interior of the crucible  142  to a perimeter thereof. The hot nitrogen is then exhausted to the environment either through High Efficiency Particulate Air (HEPA) filter (not shown) or to a facility exhaust (not shown). This center injection configuration facilitates the faster cooling of the center of the wafers  108 , and therefore is ideal to minimize the center/edge temperature differential of the bottom wafer or wafers, which could otherwise result in damage due to slip-dislocation of the crystal lattice structure.  
      As noted above, to increase or extend the life of bottom heating element  112 - 1  the idle temperature can be set higher, closer to the desired processing temperature to reduce the effects of thermal cycling. In addition, it is also desirable to periodically bake out the heating elements  112 - 1  in an oxygen rich environment to promote the formation of a protective oxide surface coat. For example, where the resistive heating elements are formed from an Aluminum containing alloy, such as Kanthal®, baking out the heating elements  112 - 1  in an oxygen rich environment promotes an alumna oxide surface growth. Thus, the insulating block  140  can further include an oxygen line (not shown) to promote the formation of the protective oxide surface coat during bake out of the heating elements  112 - 1 . Alternatively, oxygen for bake out can be introduced through the purge line used during processing to supply cooling nitrogen via a three-way valve.  
       FIG. 3  is a cross-sectional view of a portion of a thermal processing apparatus  100 .  FIG. 3  shows the thermal processing apparatus  100  while the wafers  108  are being loaded or unloaded, that is while the pedestal  130  is in the lowered position. In this mode of operation, the thermal processing apparatus  100  further includes a thermal shield  146  that can be rotated or slid into place above the pedestal  130  and the lower wafer  108  in the boat  106 . To improve the performance of the thermal shield  146 , generally the thermal shield is reflective on the side facing the heating elements  112 - 1  and absorptive on the side facing the wafers  108 . Purposes of the thermal shield  146  include increasing the rate of cooling of the wafers  108  lower down in the boat  106 , and assisting in maintaining the idle temperature of the pedestal  130  and bottom heating elements  112 - 1  to decrease the time required to ramp up the process chamber  102  to the desired processing temperature. An embodiment of a thermal processing apparatus having a thermal shield will now be described in further detail with reference to  FIGS. 3 through 6 .  
       FIG. 3  also shows an embodiment of a thermal processing apparatus  100  having pedestal heating elements  112 - 1  and a thermal shield  146 . In the embodiment shown, the thermal shield  146  is attached via arm  148  to a rotable shaft  150  that is turned by an electric, pneumatic or hydraulic actuator to rotate the thermal shield  146  into a first position between the heated pedestal  130  and the lowest of the wafers  108  in the boat  106  during the pull or unload cycle, and removed or rotated to a second position not between the pedestal and the wafers during at least a final portion or end of the push or load cycle, just before the bottom of the boat  106  enters into the chamber  102 . Preferably, the rotable shaft  150  is mounted on or affixed to the mechanism (not shown) used for raising and lowering the pedestal  130 , thereby enabling the thermal shield  146  to be rotated into position as soon as the top of the pedestal has cleared the process chamber  102 . Having the shield  146  in place during the load cycle enables the heating elements  112 - 1  to be heated to a desired temperature more rapidly than would otherwise be possible. Similarly, during unload cycle the shield  146  helps in cooling the wafers, particularly those closer to the pedestal, by reflect the heat radiating from the pedestal heating elements  112 - 1 .  
      Alternatively, the rotable shaft  150  can be a mounted on or affixed to another part of the thermal processing apparatus  100  and adapted to move axially in synchronization with the pedestal  130 , or to rotate the thermal shield  146  into position only when the pedestal is fully lowered.  
       FIG. 4  is a diagrammatic illustration of the pedestal heating elements  112 - 1  and thermal shield  146  of  FIG. 3  illustrating the reflection of thermal energy or heat radiating from the bottom heating elements back to the pedestal  130  and the absorption of thermal energy or heat radiating from the lower wafer  108  in the batch or stack of wafers. It has been determined that the desired characteristics, high reflectivity and high absorptivity, can be obtained using a number of different materials, such as metals, ceramic, glass or polymeric coatings, either individually or in combination. By way of example the following table list various suitable materials and corresponding parameters.  
                       TABLE I                       Material   Absorptivity   Reflectivity                                            Stainless Steel   0.2   0.8       Opaque Quartz   0.5   0.5       Polished Aluminum   0.03   0.97       Silicon Carbide   0.9   0.1                    
      According to one embodiment the thermal shield  146  can be made from a single material such as silicon-carbide (SiC), opaque quartz or stainless steel which has been polished on one side and scuffed, abraded or roughened on the other. Roughening a surface of the thermal shield  146  can significantly change its heat transfer properties, particularly its reflectivity.  
      In another embodiment, the thermal shield  146  can be made from two different layers of material.  FIG. 5  is a diagrammatic illustration of a thermal shield  146  having a top layer  152  of material such as SiC or opaque quartz, with a high absorptivity and a lower layer  154  of material or metal, such as polished stainless steel or polished aluminum, with a high reflectivity. Although shown as having approximately equal thicknesses, it will be appreciated that either the top layer  152  or the lower layer  154  can have a relatively greater thickness depending on specific requirements for the thermal shield  146 , such as minimizing thermal stresses between the layers due to differences in coefficients of thermal expansion. For example, in certain embodiments the lower layer  154  can be an extremely thin layer or film of polished metal deposited, formed or plated on a quartz plate that forms the top layer  152 . The materials can be integrally formed or interlocking, or joined by conventional means such as bonding or fasteners.  
      In yet another embodiment, the thermal shield  146  further includes an internal cooling channel  156  to further insulate the wafers  108  from the bottom heating elements  112 - 1 . In one version of this embodiment, shown in  FIG. 6 , the cooling channel  156  is formed between two different layers  152  and  154  of material. For example, the cooling channel  156  can be formed by milling or any other suitable technique in a highly absorptive opaque quartz layer  152 , and be covered by a metal layer  154  or coating such as a Titanium or Aluminum coating. Alternatively, the cooling channel  156  can be formed in the metal layer  154  or both the metal layer and the quartz layer  152 .  
       FIG. 7  is a perspective view of an embodiment of a thermal shield assembly  153  including the thermal shield  146 , arm  148 , rotable shaft  150  and an actuator  155 .  
      As shown in  FIG. 8 , the thermal processing apparatus  100  further includes a shutter  158  that can be rotated or slid or otherwise moved into place above the boat  106  to isolate the process chamber  102  from the outside or load port environment when the pedestal  130  is in the fully lowered position. For example, the shutter  158  can be slid into place above the carrier  106  when the pedestal  130  is in a lowered position, and raised to isolate the process chamber  102 . Alternatively, the shutter  158  can be rotated or swung into place above the carrier  106  when the pedestal  130  is in a lowered position, and subsequently raised to isolate the process chamber  102 . Optionally, the shutter  158  may be rotated about or relative to threaded screw or rod to simultaneously raise the shutter to isolate the process chamber  102  as it is swung into place above the carrier  106 .  
      For a process chamber  102  that is normally operated under vacuum, such as in a CVD system, the shutter  158  could form a vacuum seal against the base-plate  124  to allow the process chamber  102  to be pumped down to the process pressure or vacuum. For example, it may be desirable to pump down the process chamber  102  between sequential batches of wafers to reduce or eliminate the potential for contaminating the process environment. Forming a vacuum seal is preferably done with a large diameter seal, such as an o-ring, and thus the shutter  158  can desirably include a number of water channels  160  to cool the seal. In the embodiment shown in  FIG. 8  the shutter  158  seals with the same o-ring  132  used to seal with the crucible  142  when the pedestal  130  is in the raised position.  
      For a thermal processing apparatus  130  in which the process chamber  102  is normally operated at atmospheric pressure, the shutter  158  is simply an insulating plug designed to reduce heat loss from the bottom of the process chamber. One embodiment for accomplishing this involves the use of an opaque quartz plate, which may or may not further include a number of cooling channels underneath or internal thereto.  
      When the pedestal  130  is in the fully lowered position, the shutter  158  is moved into position below the process chamber  102  and then raised to isolate the process chamber by one or more electric, hydraulic or pneumatic actuators (not shown). Preferably, the actuators are pneumatic actuators using from about 15 to 60 pounds per square inch gauge (PSIG) air, which is commonly available on thermal processing apparatus  100  for operation of pneumatic valves. For example, in one version of this embodiment the shutter  158  can comprise a plate having a number of wheels attached via short arms or cantilevers to two sides thereof. In operation, the plate or shutter  158  is rolled into position beneath the process chamber  102  on two parallel guide rails. Stops on the guide rails then cause the cantilevers to pivot translating the motion of the shutter  158  into an upward direction to seal the process chamber  102 .  
      As shown in  FIG. 9 , the thermal processing apparatus  100  further includes a magnetically coupled wafer rotation system  162  that rotates the support  104  and the boat  106  along with the wafers  108  supported thereon during processing. Rotating the wafers  108  during processing improves within wafer (WIW) uniformity by averaging out any non-uniformities in the heating elements  112  and in process gas flows to create a uniform on-wafer temperature and species reaction profile. Generally, the wafer rotation system  162  is capable of rotated the wafers  108  at a speed of from about 0.1 to about 10 revolutions per minute (RPM).  
      The wafer rotation system  162  includes a drive assembly or rotating mechanism  164  having a rotating motor  166 , such as an electric or pneumatic motor, and a magnet  168  encased in a chemically resistive container, such as annealed polytetrafluoroethylene or stainless steel. A steel ring  170  located just below the insulating block  140  of the pedestal  130 , and a drive shaft  172  with the insulating block transfer the rotational energy to another magnet  174  located above the insulating block in a top portion of the pedestal. The steel ring  170 , drive shaft  172  and second magnet  174  are also encased in a chemically resistive container compound. The magnet  174  located in the side of the pedestal  130  magnetically couples through the crucible  142  with a steel ring or magnet  176  embedded in or affixed to the support  104  in the process chamber  102 .  
      Magnetically coupling the rotating mechanism  164  through the pedestal  130  eliminates the need for locating it within the processing environment or for having a mechanical feedthrough, thereby eliminating a potential source of leaks and contamination. Furthermore, locating rotating mechanism  164  outside and at some distance from the processing minimizes the maximum temperature of to which it is exposed, thereby increasing the reliability and operating life of the wafer rotation system  162 .  
      In addition to the above, the wafer rotation system  162  can further include one or more sensors (not shown) to ensure proper boat  106  position and proper magnetic coupling between the steel ring or magnet  176  in the process chamber  102  and the magnet  174  in the pedestal  130 . A sensor which determines the relative position of the boat  106 , or boat position verification sensor, is particularly useful. In one embodiment, the boat position verification sensor includes a sensor protrusion (not shown) on the boat  106  and an optical or laser sensor located below the base-plate  124 . In operation, after the wafers  108  have been processed and the pedestal  130  is lowered about 3 inches below the base-plate  124 . There, the wafer rotation system  162  is commanded to turn the boat  106  until the boat sensor protrusion can be seen. Then, the wafer rotation system  162  is operated to align the boat so that the wafers  108  can be unloaded. After this is done, the boat is lowered to the load/unload height. After the initial check, it is only capable of verifying the boat location from the flag sensor.  
      As shown in  FIG. 10 , improved injectors  216  are preferably used in the thermal processing apparatus  100 . The injectors  216  are distributive or cross(X)-flow injectors  216 - 1  in which process gas or vapor is introduced through injector openings or orifices  180  on one side of the wafers  108  and boat  106  and caused to flow across the surfaces of the wafers in a laminar flow to exit exhaust ports or slots  182  in the chamber line  120  on opposite the side. X-flow injectors  116 - 1  improve wafer  108  to wafer uniformity within a batch of wafers  108  by providing an improved distribution of process gas or vapor over earlier up-flow or down flow configurations.  
      Additionally, X-flow injectors  216  can serve other purposes, including the injection of gases for cool-down (e.g., helium, nitrogen, hydrogen) for forced convective cooling between the wafers  108 . Use of X-flow injectors  216  results in a more uniform cooling between wafers  108  whether disposed at the bottom or top of the stack or batch and those wafers that are disposed in the middle, as compared with earlier up-flow or down flow configurations. Preferably, the injector  216  orifices  180  are sized, shaped and position to provide a spray pattern that promotes forced convective cooling between the wafers  108  in a manner that does not create a large temperature gradient across the wafer.  
       FIG. 11  is a cross-sectional side view of a portion of the thermal processing apparatus  100  of  FIG. 10  showing illustrative portions of the injector orifices  180  in relation to the chamber liner  120  and the exhaust slots  182  in relation to the wafers  108 .  
       FIG. 12  is a plan view of a portion of the thermal processing apparatus  100  of  FIG. 10  taken along the line A-A of  FIG. 10  showing laminar gas flow from the orifices  180 - 1  and  180 - 2  of primary and secondary injectors  184 ,  186 , across an illustrative one of the wafers  108  and to exhaust slots  182 - 1  and  182 - 2  according to one embodiment. It should be noted that the position of the exhaust slot  182  as shown in  FIG. 10  have been shifted from the position of exhaust slots  182 - 1  and  182 - 2  shown in  FIG. 12  to allow illustration of the exhaust slot and injector  116 - 1  in a single a cross-sectional view of a thermal processing apparatus. It should also be noted that the dimensions of the injectors  184 ,  186 , and the exhaust slots  182 - 1  and  182 - 2  relative to the wafer  108  and the chamber liner  120  have been exaggerated to more clearly illustrate the gas flow from the injectors to the exhaust slots.  
      Also as shown in  FIG. 12 , the process gas or vapor is initially directed away from the wafers  108  and toward the liner  120  to promote mixing of the process gas or vapor before it reaches the wafers. This configuration of orifices  180 - 1  and  180 - 2  is particularly useful for processes or recipes in which different reactants are introduced from each of the primary and secondary injectors  184 ,  186 , for example to form a multi-component film or layer.  
       FIG. 13  is another plan view of a portion of the thermal processing apparatus  100  of  FIG. 10  taken along the line A-A of  FIG. 10  showing an alternative gas flow path from the orifices  180  of the primary and secondary injector  184 ,  186 , across an illustrative on of the wafer  108  and to the exhaust slots  182  according to another embodiment.  
       FIG. 14  is another plan view of a portion of the thermal processing apparatus  100  of  FIG. 10  taken along the line A-A of  FIG. 10  showing an alternative gas flow path from the orifices  180  of the primary and secondary injector  184 ,  186 , across an illustrative on of the wafer  108  and to the exhaust slots  182  according to yet another embodiment.  
       FIG. 15  is another plan view of a portion of the thermal processing apparatus  100  of  FIG. 10  taken along the line A-A of  FIG. 10  showing an alternative gas flow path from the orifices  180  of the primary and secondary injector  184 ,  186 , across an illustrative on of the wafer  108  and to the exhaust slots  182  according to still another embodiment.  
       FIG. 16  is a cross-sectional view of a thermal processing apparatus  100  having two or more up-flow injectors  116 - 1  and  116 - 2  according to an alternative embodiment. In this embodiment, process gas or vapor admitted from the process injectors  116 - 1  and  116 - 2  having respective outlet orifices low in the process chamber  102  flows up and across the wafers  108 , and spent gases exit exhaust slots  182  in the top of the liner  120 . An up-flow injector system is also shown in  FIG. 1 .  
       FIG. 17  is a cross-sectional view of a thermal processing apparatus  100  having a down-flow injector system according to an alternative embodiment. In this embodiment, process gas or vapor admitted from process injectors  116 - 1  and  116 - 2  having respective orifices high in the process chamber  102  flows down and across the wafers  108 , and spent gases exit exhaust slots  182  in the lower portion of the liner  120 .  
      Advantageously, the injectors  116 ,  216 , and/or the liner  120  can be quickly and easily replaced or swapped with other injectors and liners having different points for the injection and exhausting of the process gas from the process zone  128 . It will be appreciated by those skilled in the art that the embodiment of the x-flow injector  216  shown in  FIG. 10  adds a degree of process flexibility by enabling the flow pattern within the process chamber  102  to be quickly and easily changed from a cross-flow configuration, as shown in  FIG. 10 , to an up-flow configuration, as shown in  FIGS. 1 and 16 , or a down-flow configuration, as shown in  FIG. 17 . This can be accomplished through the use of easily installable injector assemblies  216  and liners  120  to convert the flow geometry from cross-flow to an up-flow or down-flow.  
      The injectors  116 ,  216 , and the liner  120  can be separate components, or the injector can be integrally formed with liner as a single piece. The latter embodiment is particular useful in applications where it is desirable to frequently change the process chamber  102  configuration.  
      An illustrative method or process for operating the thermal processing apparatus  100  is described with reference to  FIG. 18 .  FIG. 18  is a flowchart showing steps of a method for thermally processing a batch of wafers  108  wherein each wafer of the batch of wafers is quickly and uniformly heated to the desired temperature. In the method, the pedestal  130  is lowered, and the thermal shield  142  is moved into a position while the pedestal  130  is lowered to reflect heat from the bottom heating element  112 - 1  back to the pedestal  130  to maintain the temperature thereof, and to insulate the finished wafers  108  (step  190 ). Optionally, the shutter  158  is moved into position to seal or isolate the process chamber  102  (step  192 ), and power is applied to the heating elements  112 - 2 ,  112 - 3 , to begin pre-heating the process chamber  102  to or maintain at an intermediate or idling temperature (step  194 ). A carrier or boat  106  loaded with new wafers  108  is positioned on the pedestal  130  (step  196 ). The pedestal  130  is raised to position the boat in the process zone  128 , while simultaneously removing the shutter  158 , the thermal shield  142 , and ramping-up the bottom heating element  112 - 1  to preheat the wafers to an intermediate temperature (step  197 ). Preferably, the thermal shield  142  is removed just before the boat  106  is positioned in the process zone  128 . A fluid, such as a process gas or vapor, is introduced on one side of the of wafers  108  through a plurality of injection ports  180  (step  198 ). The fluid flows from the injection ports  180  across surfaces of the wafers  108  to exhaust ports  182  positioned in the liner  120  on the opposite side of the wafers relative to the injection ports (step  199 ). Optionally, the boat  106  can be rotated within the process zone  128  during thermal processing of the batch of wafers  108  to further enhance uniformity of the thermal processing, by magnetically coupling mechanical energy through the pedestal  130  to the carrier or boat  106  to reposition it during thermal processing of the wafers (step  200 ).  
      A method or process for a thermal processing apparatus  100  according to another embodiment will now be described with reference to  FIG. 19 .  FIG. 19  is a flowchart showing steps of an embodiment of a method for thermally processing a batch of wafers  108  in a carrier. In the method, an apparatus  100  is provided having a process chamber  102  with dimensions and a volume not substantially larger than necessary (guard heaters absent) to accommodate the carrier  106  with the wafers  108  held therein. The pedestal  130  is lowered, and the boat  106  with the wafers  108  held therein positioned thereon (step  202 ). The pedestal  130  is raised to insert the boat in the process chamber  102 , while simultaneously preheating the wafers  108  to an intermediate temperature (step  204 ). Power is applied to the heating elements  112 - 1 ,  112 - 2 ,  112 - 3 , each disposed proximate to at least one of the top wall  134 , the side wall  136  and the bottom wall  138  of the process chamber  102  to begin heating the process chamber (step  206 ). Optionally, power to at least one of the heating elements is adjusted independently to provide a substantially isothermal environment at a desired temperature in a process zone  128  in the process chamber  102  (step  208 ). When the wafers  108  have been thermally processed, and while maintaining the desired temperature in the process zone  128 , the pedestal  130  is lowered, and the thermal shield  142  is moved into position to insulate the finished wafers  108  and to reflect heat from the bottom heating element  112 - 1  back to the pedestal  130  to maintain the temperature thereof (step  210 ). Also, optionally, the shutter  158  is moved into position to seal or isolate the process chamber  102 , and power applied to the heating elements  112 - 2 ,  112 - 3 , to maintain the temperature of the process chamber (step  212 ). The boat  106  is then removed from the pedestal  130  (step  214 ), and another boat loaded with a new batch of wafers to be processed positioned on the pedestal (step  216 ). The shutter  158  is repositioned or removed (step  218 ), and the thermal shield withdrawn or repositioned to preheat the wafers  108  in the boat  106  to an intermediate temperature while simultaneously raising the pedestal  130  to insert the boat into the process chamber  102  to thermally process the new batch of wafers (step  220 ).  
      It has been determined that the thermal processing apparatus  100  provided and operated as described above, reduces the processing or cycle time by about 75% over conventional systems. For example, a conventional large batch thermal processing apparatus may process  100  product wafers in about 232 minutes, including pre-processing and post-processing time. The inventive thermal processing apparatus  100  performs the same processing on a mini-batch of 25 product wafers  108  in about 58 minutes.  
      An injection system in accordance with one embodiment of the present invention will be now described with reference to  FIGS. 20 through 32 .  
      Injectors having injection ports or orifices distributed in elongated tubes have been used in both horizontal and vertical furnaces to control gas concentration across the surface of substrates. Typically, two or more injectors are used to distribute similar or different gases depending on specific applications. For example, for deposition of P-doped polysilicon, injectors with distributed injection ports have been used to introduce PH 3  gas across a wafer load in a furnace to provide a uniform gas concentration. Injectors with distributed injection ports are used to ensure that the properties of the deposited films are the same across the wafer load. Traditionally, the injectors are fixed, i.e., the direction of injection ports or orifices in the injectors are fixed and typically face toward the center of wafers. Even so, films deposited on the wafers still exhibit an undesirable within-wafer uniformity. The uniformity, quality and repeatability of deposited films depend on not only gas flow rates, concentration, pressure and temperature, but also gas flow pattern and distribution of gases. The present invention provides an injection system that is angularly adjustable to promote the momentum transfer of “ballistic mixing” of different gases to provide improved flow uniformity and thus improved quality and uniformity of the deposited films. In general, the injection system of the present invention comprises one or more elongated injection tubes having a plurality of injection ports or orifices distributed in the tubes for directing flow of reactant and other gases across the surface of each substrate. The elongated injection tubes are rotatable about an axis in 360 degrees.  
       FIG. 20  shows a thermal processing apparatus  230  including an injection system  250  according to one embodiment of the present invention. To simplify description of the invention, elements not closely relevant to the invention are not indicated in the drawing and described. In general, the apparatus  230  includes a vessel  234  that houses a process chamber  236  having a support  238  adapted for receiving a carrier  240  with a batch of wafers  242  held therein. The apparatus  230  includes heat source or furnace  244  for raising temperature of the wafers  242  to the desired temperature for thermal processing. A cross-flow liner  232  is provided to increase the concentration of processing gas or vapor near wafers  242  and reduce contamination of wafers  242  from flaking or peeling of deposits that can form on interior surfaces of the process chamber  236 . The liner  232  is patterned to conform to the contour of the wafer carrier  240  and sized to reduce the gap between the wafer carrier  240  and the liner wall. The liner  232  is mounted to the base plate  246  and sealed. A cross-flow injection system  250  is disposed between the liner  232  and the wafer carrier  240 . Gases are introduced through a plurality of injection ports or orifices  252  from one side of the wafers  242  and carrier  240  across the surface of the wafers in a laminar flow as described below. A plurality of slots  254  are formed in the liner  232  on the opposite side to exhaust gases or reaction by-product.  
      The cross-flow injection system  250  includes one or more elongated injection tubes.  FIG. 21  shows an elongated injection tube  256  according to one embodiment of the present invention. As shown, a plurality of injection ports or orifices  252  are provided in the elongated injection tube  256 . In one embodiment, the spacing between the injection ports  252  is such that when the injection tube  256  is installed, each injection port  252  is positioned at a height between two adjacent wafers  242  supported in the wafer carrier  240  so that the gas exiting the injection port  252  is caused to flow in a path formed between the adjacent wafers. In another embodiment, the spacing between and number of the injection ports or orifices  252  in the injection tubes  256  cooperates with the spacing between and number of slots  254  in the liner  232  so that excessive gas or reaction by-products are exhausted from the corresponding slot in the liner. The injection system  250  of the present invention may comprise one or more elongated injection tubes  256  as illustrated in  FIG. 21 . The elongated injection tube  256  can be made of any metal, ceramic, crystalline or glass material that is capable of withstanding the thermal and mechanical stresses of high temperature and high vacuum operation, and which is resistant to erosion from gases and vapors used or released during processing. Preferably, the injection tube is made from an opaque, translucent or transparent quartz glass. In one embodiment, the injection tube is made from quartz.  
       FIG. 22  is a partial cross-sectional view of a thermal processing apparatus  230  showing connection of the injection system  250  with liner  232  and base plate  246 . The elongated injection tube  256  is coupled to an injection inlet  262  in the base plate  246  and sealed to the base plate by O-rings  264 . The elongated injection tubes  256  are engaged with the liner  232  through a clamp block  266 , as shown in detail in  FIG. 23 . A lock pin  268  locks the clamp block  266  to the base plate  246 . Reactants or other gases are introduced into the injection tube  256  through inlet  262 .  
       FIG. 24  is a partial plan view of a top plate  270  of a liner  232  having openings  272  for receiving one or more elongated injection tubes  256 . As shown, the openings  272  in the top plate  270  are provided with notches  274  for stabilizing the elongated injection tubes  256  and orienting the injection ports  252  in the tubes  256  to a specific direction. While three notches  274 A-C are shown in each of the openings  272  for illustrative purpose, it should be noted that any number of notches can be provided so that the elongated injection tubes  256  can be rotated and adjusted about an axis in  360  degrees and the injection ports  258  can be oriented in any direction as desired. In one embodiment, the elongated tube  256  includes an index pin (not shown) for locking the elongated tube  256  in one of the notches  274  in the opening  272 . In another embodiment, the injection ports or orifices  252  in the tubes  256  are formed in line with the index pin. Thus, when the elongated tube  256  is installed, the index pin is locked in one of the notches  274  and the injection ports  252  in the tube  256  are oriented to a direction as indicated by the index pin locked in the notch.  
      For example, when the index pin in the elongated tube  256  is locked in notch  274 A, the injection ports  252  are oriented to face the inner surface of the liner  232 . Gases exiting the injection ports  252  impinge the wall and mix prior to flowing across the surface of each substrate  242 . In another embodiment, the index pin in the elongated tube  256  is locked in notch  274 B. The injection ports  252  in each injection tube  256  are oriented to face each other. Gases exiting the injection ports  252  impinge each other and mix prior to flowing across the surface of each substrate  242 . In a further embodiment, the index pin in the elongated tube  256  is locked in notch  274 C so that the injection ports  252  are oriented to face the center of the substrate  242 . The number of notches formed in the openings can be as many as desired so that the elongated tube  256  can be rotated in 360 degrees and stabilized in a desired position, and accordingly the injection ports  252  can be oriented to a desired direction.  
      Of advantage, the injection system of the present invention enables full freedom of rotation of the injection ports to promote the momentum transfer of “ballistic mixing” of gases, which may vary in different processes. The orientation of the injection ports or orifices that influence gas mixing and flow direction can be adjusted on a run-to-run basis without the need of process chamber modification.  
      In one embodiment, the injection system of the present invention is used in connection with a cross flow liner having a bulging section. U.S. application Ser. No. ______ (Attorney Docket No. 33586/US/1) filed currently with this application further describes a cross-flow liner, the disclosure of which is hereby incorporated by reference in its entirety.  FIGS. 25-26  show a cross-flow liner  276  that can be used in connection with the injection system  250  of the present invention. As shown, the cross-flow liner  276  includes a cylinder  278  having a close end  280  and open end  282 . The cylinder  278  is provided with a longitudinal bulging section  284  to accommodate a cross-flow injection system  250 . A plurality of latitudinal slots  286  are provided longitudinally in the cylinder  278  on the side opposite to the bulging section  284  to exhaust gases and reaction by-products. The cross-flow liner  276  is sized and patterned to conform to the contour of the wafer carrier  240  and the carrier support  238 . In one embodiment, the liner  276  comprises a first section  288  sized to conform to the wafer carrier  240  and a second section  290  sized to conform to the carrier support  238 . The diameter of the first section  288  may differ from the diameter of the second section  290 , i.e., the liner  276  may be “stepped” to conform to the wafer carrier  240  and carrier support  238  respectively. In one embodiment, the first section  288  of the liner  276  has an inner diameter that constitutes about 104 to 110% of the carrier outer diameter. In another embodiment, the second section  290  of the liner  276  has an inner diameter that constitutes about 115 to 120% of outer diameter of the carrier support  238 . The second section  290  may be provided with one or more heat shields to protect seals such as O-rings from being overheated by heating elements. Of advantage, the cross-flow liner  276  with a longitudinal bulging section  284  can be made conformal to the contour of the wafer carrier  240  to reduce the gap between the liner  276  and the wafer carrier  240 . This helps reduce vortices and stagnation in the gap regions between the liner inner wall and the wafer carrier, and thus improve flow uniformity, which in turn improves the quality, uniformity, and repeatability of the deposited film.  
      In one embodiment shown in  FIG. 27 , two elongated injection tubes  256  are installed in a bulging section  284  of a cross-flow liner  276 . The elongated tubes  256  are rotated and adjusted so that the injection ports  252  are oriented to face the inner surface of the liner  276 . As shown in  FIG. 27 , gases exiting the injection ports  252  impinge the liner wall and mix in the bulging section  284  prior to flowing across the surface of each substrate  242 . In another embodiment shown in  FIG. 28 , two elongated tubes  256  are rotated and adjusted so that the injection ports  252  are oriented to face each other. As shown in  FIG. 28 , gases exiting the injection ports  252  impinge each other and mix in the bulging section  284  prior to flowing across the surface of each substrate  242 . In a further embodiment shown in  FIG. 29 , two elongated tubes  256  are rotated and adjusted so that the injection ports  252  are oriented to face the center of the substrate  242 .  
      The following examples are provided to further illustrate the present invention and are not intended to limit the scope of the invention in any way.  
     EXAMPLE 1  
      This example illustrates deposition of silicon nitride using dichlorosilane (DCS) and NH 3  gases. The deposition is performed in a thermal processing apparatus including an injection system of the present invention. The injection system comprises a first injection tubes for introducing DCS gas and a second injection tube for introducing NH 3  gas. Each of the first and second injection tubes is provided with a plurality of ports or orifices for directing gas flow across the surface of each substrate.  
      In one variation, the elongated tubes are rotated and adjusted so that the injection ports are oriented to face the inner surface of the liner. DCS and NH 3  gases exiting the injection ports away from wafers and impinge the liner inner surface prior to flowing across the surface of each substrate.  
      In another variation, the elongated tubes are rotated and adjusted so that the injection ports are oriented to face the center of the substrate. DCS and NH 3  gases exit the injection ports and flow across the surface of each substrate.  
       FIG. 30  is a Computational Fluid Dynamics (CFD) demonstration showing a uniform flow of DCS and NH 3  gases across the surface of the substrate in an injector configuration where the injection ports are oriented toward the center of the substrate, creating radially-inward flow of the gases. In this case, the mass difference between DCS and NH 3  is relatively less (DCS=101, NH 3 =17), thus the gas velocities are more similar.  
     EXAMPLE 2  
      This example illustrates deposition of silicon nitride using bis tertiarybutylamino silane (BTBAS) and NH 3  gases. The deposition is performed in a thermal processing apparatus including an injection system of the present invention. The injection system comprises a first injection tube for introducing BTBAS gas and a second injection tube for introducing NH 3  gas. Each of the first and second injection tubes is provided with a plurality of ports or orifices for directing gas flow across the surface of each substrate.  
      In one variation, the elongated tubes are rotated and adjusted so that the injection ports are oriented to face the inner surface of the liner. BTBAS and NH 3  gases exiting the injection ports away from wafers and impinge the liner wall prior to flowing across the surface of each substrate.  
      In another variation, the elongated tubes are rotated and adjusted so that the injection ports are oriented to face each other. BTBAS and NH 3  gases exit the injection ports and impinge and mix prior to flowing across the surface of each substrate.  
       FIG. 31  is a CFD demonstration showing a uniform flow of BTBAS and NH 3  gases across the surface of the substrate in an injector configuration where the injection ports are oriented to face each other, creating converging flow of the gases. In this case, the molecular weight of BTBAS is 174, the molecular weight of NH 3  is 17. The recoil and mixing of BTBAS and NH 3  ensure a uniform gas velocity as the gases flow across the wafer and results in exceptional within wafer uniformity of &lt;1.5% (1 sigma) on a 300 mm wafer.  
     EXAMPLE 3  
      This example illustrates deposition of aluminum oxide (Al 2 O 3 ) using trimethyl aluminum (TMA) and ozone (O 3 ) gases. The deposition is performed in a thermal processing apparatus including an injection system of the present invention. The injection system comprises a first injection tube for introducing TMA gas and a second injection tube for introducing O 3  gas. Each of the first and second injection tubes is provided with a plurality of ports or orifices for directing gas flow across the surface of each substrate.  
      In one variation, the elongated tubes are rotated and adjusted so that the injection ports are oriented to face the inner surface of the liner. TMA and O 3  gases exiting the injection ports away from wafers and impinge the liner wall prior to flowing across the surface of each substrate.  
      In one variation, the elongated tubes are rotated and adjusted so that the injection ports are oriented to face each other. TMA and O 3  gases exit the injection ports and impinge and mix prior to flowing across the surface of each substrate.  
       FIG. 32  is a CFD demonstration showing a uniform flow of TMA and O 3  gases across the surface of the substrate in an injector configuration where the injection ports are oriented to face the liner wall, creating radially outward flow of the gases. The recoil and mixing of TMA and O 3  ensure a uniform gas velocity as the gases flow across the surface of each wafer.  
      The foregoing description of specific embodiments and examples of the invention have been presented for the purpose of illustration and description, and although the invention has been described and illustrated by certain of the preceding examples, it is not to be construed as being limited thereby. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and many modifications, improvements and variations within the scope of the invention are possible in light of the above teaching. It is intended that the scope of the invention encompass the generic area as herein disclosed, and by the claims appended hereto and their equivalents.