Patent Publication Number: US-2020294819-A1

Title: Systems and Methods for Substrate Cooling

Description:
FIELD OF THE INVENTION 
     The invention relates generally to an apparatus and a method for cooling a substrate, such as a semiconductor wafer. 
     BACKGROUND OF THE INVENTION 
     A semiconductor device is generally fabricated by repetitively performing a series of processes, such as photolithography, diffusion, etching, ion implantation, deposition, and metallization processes, on a substrate (e.g., a wafer). The manufacturing equipment for fabricating a semiconductor device includes apparatus for performing each of these processes, such as a process chamber into which a substrate is loaded to perform each process. Further, semiconductor device manufacturing equipment can also include at least one load lock chamber connected to a process chamber, a cassette or carrier that can hold a number of substrates, and a mechanical transfer mechanism for moving substrates among different equipment, including the process chamber and the load lock chamber. 
     In a typical semiconductor fabrication operation, at least one substrate is loaded onto a cassette and moved from an input stage into the load lock chamber while the load lock chamber is vented to atmosphere. The load lock chamber is then pumped down to a desired high vacuum pressure. Thereafter, the substrate in the load lock chamber is mechanically transferred to a process chamber for processing, where the substrate is subjected to high processing temperature. When processing is completed, the substrate is moved from the process chamber and placed into a cooling station prior to returning the substrate to the load lock chamber. Cooling of a substrate is necessary to avoid damaging temperature-sensitive apparatus associated with handling post-process wafers. Exemplary temperature-sensitive apparatus include, but are not limited to, the atmosphere robot arm and its associated components, as well as plastic wafer storage cassettes. After cooling, the substrate is transferred back to the original cassette located in the load lock chamber. Subsequent to the other substrates in the load lock chamber being processed in a similar manner, the load lock chamber is vented to atmospheric pressure. 
     A load lock chamber thus functions as a transition chamber between the process chamber, which is maintained under vacuum, and the input stage, which is under atmospheric pressure. A load lock chamber allows substrates to be transferred into the process chamber without venting the process chamber to atmosphere, thereby reducing processing times in the process chamber and minimizing exposure of the process chamber to atmospheric contamination. 
     SUMMARY OF THE INVENTION 
     The present invention provides a load lock chamber with integrated cooling capability. Specifically, the cooling systems and methods of the present invention is implemented in a load lock chamber to take advantage of the mechanisms that are already in place (e.g., the existing gas delivery system) and can be adapted for cooling a substrate. This integrated apparatus increases system throughput and decreases physical footprint because processed substrates can be transferred from a process chamber into a load lock chamber without the need for separate cooling. Further, the systems and methods of the present invention facilitates uniform cooling of a substrate in the load lock chamber. 
     In one aspect, the invention features an apparatus for cooling a substrate having (i) a top surface and a bottom surface and (i) at least one vertical side surface corresponding to a substrate thickness. The apparatus comprises a chamber configured to receive the substrate. The chamber comprises a plurality of sidewall sections surrounding the substrate and oriented in a vertical direction substantially parallel to the vertical side surface of the substrate. The apparatus also includes at least one gas inlet port on a first side wall section of the chamber. The gas inlet port is configured to introduce a cooling gas into the chamber in a lateral direction parallel to the top and bottom surfaces of the substrate. The apparatus further includes at least one gas outlet port on a second side wall section of the chamber located substantially opposite of the first side wall section of the chamber with the substrate disposed therebetween. The gas outlet port is configured to conduct at least a portion of the cooling gas out of the chamber along the lateral direction. The gas inlet port and the gas outlet port, in combination, are adapted to cause the cooling gas to cooperatively flow across the top and bottom surfaces of the substrate in the lateral direction to cool the substrate. 
     In another aspect, a method is provided for cooling a substrate having (i) a top surface and a bottom surface and (i) at least one vertical side surface corresponding to a substrate thickness. The method includes securing the substrate in a chamber. The chamber comprises a plurality of sidewall sections surrounding the substrate and oriented in a vertical direction substantially parallel to the vertical side surface of the substrate. The method also includes introducing, via at least one gas inlet port, a cooling gas into the chamber in a lateral direction parallel to the top and bottom surfaces of the substrate. The gas inlet port is located on a first side wall section of the chamber. The method further includes conducting, via at least one gas outlet port, at least a portion of the cooling gas out of the chamber along the lateral direction. The gas outlet port is located on a second side wall section of the chamber substantially opposite of the first side wall section of the chamber with the substrate disposed therebetween. The method also includes cooling, by a flow of the cooling gas from the gas inlet port to the gas outlet port, the top and bottom surfaces of the substrate along the lateral direction. 
     Any of the above aspects can include one or more of the following features. In some embodiments, the at least one gas outlet port is substantially aligned with the substrate in the vertical direction to facilitate cooling of the top and bottom surfaces of the substrate. In some embodiments, the at least one gas inlet port is substantially aligned with the substrate in the vertical direction. 
     In some embodiments, at least one bumper is provided that is located in the chamber. The bumper is raised in the vertical direction to prevent lateral movement of the substrate caused by the cooling gas flow. In some embodiments, the bumper is integrated with a pad in the chamber on which the substrate is placed. 
     In some embodiments, a clamping pin is provided that is located in the chamber. The clamping pin is adapted to exert a physical pressure on the substrate in the vertical direction to prevent at least one of a vertical or lateral movement of the substrate caused by the cooling gas flow. In some embodiments, the clamping pin is retractable in the vertical direction. 
     In some embodiments, at least one second gas inlet port is provided that is located on a top wall of the chamber. The second gas inlet port is configured to introduce a second gas into the chamber in the vertical direction. In some embodiments, the second gas inlet port is adapted to conduct the second gas to exert a gas pressure on the substrate in the vertical direction to prevent at least one of a vertical or lateral movement of the substrate in the chamber. 
     In some embodiments, the chamber is a load lock chamber. In some embodiments, one or more valves are included in a gas delivery system and are in fluid communication with the gas inlet port. The valves are adjustable to provide variable flow rate of the cooling gas via the gas inlet port to control a cooling rate of the substrate. 
     Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating the principles of the invention by way of example only. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages of the technology described above, together with further advantages, may be better understood by referring to the following description taken in conjunction with the accompanying drawings. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the technology. 
         FIGS. 1 a  and 1 b    show a perspective view and a profile view, respectively, of an exemplary integrated load lock chamber, according to some embodiments of the present invention. 
         FIG. 2  shows an exemplary arrangement of multiple gas inlet ports on the first sidewall section of the integrated load lock chamber of  FIGS. 1 a  and  b   , according to some embodiments of the present invention. 
         FIG. 3  shows another exemplary arrangement of multiple gas inlet ports on the first sidewall section of the integrated load lock chamber of  FIGS. 1 a  and  b   , according to some embodiments of the present invention. 
         FIG. 4  shows an exemplary arrangement of at least one outlet port on the second sidewall section of the load lock chamber of  FIGS. 1 a  and  b   , according to some embodiments of the present invention. 
         FIG. 5  shows another exemplary arrangement of multiple outlet ports on the second sidewall section of the load lock chamber of  FIGS. 1 a  and  b   , according to some embodiments of the present invention. 
         FIG. 6  shows an exemplary mechanism for preventing movement of the substrate in the load lock chamber of  FIGS. 1 a  and  b   , according to some embodiments of the present invention. 
         FIG. 7  shows another exemplary mechanism for preventing movement of the substrate in the load lock chamber of  FIGS. 1 a  and  b   , according to some embodiments of the present invention. 
         FIG. 8  shows a retractable actuator as an example of the clamping mechanism of  FIG. 7  for preventing movement of the substrate in the load lock chamber of  FIGS. 1 a  and  b   , according to some embodiments of the present invention. 
         FIG. 9  shows yet another exemplary mechanism for preventing movement of the substrate in the load lock chamber of  FIGS. 1 a  and  b   , according to some embodiments of the present invention. 
         FIG. 10  shows an exemplary process for cooling a substrate inside of the load lock chamber of  FIGS. 1 a  and  b   , according to some embodiments of the present invention. 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIGS. 1 a  and 1 b    show a perspective view and a profile view, respectively, of an exemplary integrated load lock chamber  100 , according to some embodiments of the present invention. Even though  FIGS. 1 a  and 1 b    show the load lock chamber  100  as a single wafer device, the principles of the present invention are equally applicable to multi-wafer load lock devices, as understood by a person of ordinary skill in the art. As shown, the load lock chamber  100  includes a gas delivery manifold  102  with one or more gas inlet ports  104 , a holder  106  configured to receive and store a substrate  108 , and at least one gas outlet port  110 . Substrate  108  generally refers to a solid substance onto which a layer of a second substance is applied. In integrate circuit fabrication, the substrate  108  can be a wafer made from a semiconductor material (e.g., silicon, silicon carbide, germanium or gallium arsenide) or an insulator material (e.g., glass). The substrate  108  has a top surface  108   a  and a bottom surface  108   b , both of which can be substantially horizontal if the substrate  108  is planar. The substrate  108  also includes at least one vertical side surface (not labeled) corresponding to a substrate thickness. 
     Generally, the load lock chamber  100  is defined by multiple sidewall sections  112 , a top wall  114  and a bottom wall  116  that substantially encase the substrate  108  in the holder  106 . The sidewall sections  112  can be oriented in a vertical direction  118  substantially parallel to the vertical side surface of the substrate  108 . The top and bottom walls  114 ,  116  of the chamber  100  are positioned relative to the top and bottom surfaces  108   a ,  108   b , respectively, of the substrate  108 , such as parallel to the top and bottom surfaces of the substrate  108 . 
     The one or more gas inlet ports  104  are located on a first side wall section  112   a  of the chamber  100  and are configured to introduce a cooling gas, such as a nitrogen (N 2 ) gas, into the chamber  100  in a lateral direction  120  substantially parallel to the top surface  108   a  and the bottom surface  108   b  of the substrate  108  and perpendicular to the vertical direction  118 . In general, directing a cooling gas to flow across the top and bottom surfaces  108   a, b  of the substrate  108  facilitates heat transfer from the substrate  108  to the gas, thereby reducing the temperature of the substrate  108 . 
     The one or more gas outlet ports  110  are located on a second side wall section  112   b  of the chamber  100  and are configured to conduct at least a portion of the cooling gas out of the chamber  100  along the lateral direction  120 . The second side wall section  112   b  is located substantially opposite of the first sidewall section  112   a  with the substrate  108  and the holder  106  disposed between the two sections  112   a,b . This opposite-wall arrangement of the gas inlet ports  104  and gas outlet ports  110  allows at least a portion of the nitrogen gas to cooperatively flow across the top and/or bottom surfaces  108   a,b  of the substrate  108  to cool the substrate  108  before exiting from the chamber  100 . 
     In some embodiments, the gas manifold  102  is configured to deliver a cooling gas to the chamber  100  to cool the substrate  108 . Specifically, the gas manifold  102  can be configured to introduce as well as control the introduction of a cooling gas from at least one gas source (not shown) into the chamber  100  via one or more of the inlet ports  104  fluidly coupled to the first side wall section  112   a . In some embodiments, the gas manifold  102  is connected to the same gas source (not shown) and/or delivery system (not shown) that are traditionally used by the load lock chamber  100  to deliver a gas to the chamber  100  for adjusting the internal pressure of the chamber  100 . That is, the gas (e.g., nitrogen) that is typically used for restoring the internal pressure in the load lock chamber  100  from vacuum to atmospheric pressure may be used by the manifold  102  to cool the substrate  108  in the chamber  100 . In some embodiments, the same gas is used for both cooling and pressure adjustment. In some embodiments, the gas manifold  102  also includes one or more valves  122  in fluid communication with one or more of the gas inlet ports  104  to control the flow rate of the gas delivered therethrough. The valves  122  are adjustable, either manually by an operator or automatically by a computer numerical controller, to provide adjustable flow rate of the cooling gas delivered via one or more of the gas inlet ports  104 . This enables control of the velocity of the cooling gas, thereby providing variable cooling rate for cooling the substrate  108  in the chamber  100 . In some embodiments, the substrate  108  can be cooled at different cooling rates over time in response to variable system throughput requirements by selectively manipulating the valves  122  of the manifold  102 . In some embodiments, the valves  122  are adjusted to achieve turbulence in the cooling gas flow for the purpose of enhanced thermal transfer. For example, if two valves  122  are included in the manifold  102 , one valve  122  can be adjusted to offer slow venting by restricting the gas flow to minimize the pressure burst into the evacuated volume, while the other valve  122  can be adjusted to offer a variable flow rate, which provides an adjustable cooling rate. The resultant gas flow can be turbulent in nature. 
     As shown in  FIGS. 1 a  and 1 b   , the cooling gas is adapted to flow in the lateral direction  120  from the first side wall section  112   a  to the opposite second side wall section  112   b  of the chamber  100 . An advantage of this lateral cooling flow, in comparison to directing the cooling gas to flow in the vertical direction  118  from the top wall  114  to the bottom wall  116  of the chamber  100 , is that the substrate  108  can be cooled relatively uniformly across both its top and bottom surfaces  108   a ,  108   b . That is, the cooling gas flow rate/velocity is substantially constant across these surfaces. For example, the cooling gas flow rate/velocity can be adjusted such that the rate/velocity across the top surface  108   a  of the substrate  108  is substantially the same as the rate/velocity across the bottom surface  108   b  of the substrate  108 . Another advantage of this lateral cooling flow is that the pressure of the cooling gas does not concentrate at a particular area on the top or bottom surfaces  108   a ,  108   b  of the substrate  108  when the cooling gas is introduced into the chamber  100 , thereby minimizing the likelihood of the cooling gas damaging (e.g., breaking) the substrate  108 . 
     In some embodiments, the one or more gas inlet ports  104  and/or the one or more gas outlet ports  110  are suitably arranged on their respective sidewall sections to enhance the uniform distribution of the cooling gas across the top and bottom surfaces  108   a ,  108   b  of the substrate  108 . For example, at least one gas inlet port  104  can be substantially aligned with the substrate  108  in the vertical direction  118 , such as at about the same vertical height as the substrate  108  in the chamber  100 , to facilitate cooling of the top and bottom surfaces  108   a ,  108   b  of the substrate  108 . Likewise, at least one gas outlet port  110  can be substantially aligned with the substrate  108  in the vertical direction  118  to further enhance uniform cooling. 
       FIG. 2  shows an exemplary arrangement of multiple gas inlet ports  104  on the first sidewall section  112   a  of the integrated load lock chamber of  FIGS. 1 a  and  b   , according to some embodiments of the present invention. As shown, multiple inlet ports  104  are substantially aligned with the substrate  108  in the vertical direction  118 , such as at about the same vertical height as the substrate  108 . This arrangement ensures uniform cooling of the top and bottom surfaces  108   a ,  108   b  of the substrate  108  in the holder  106 . In addition, these inlet ports  104  can be evenly distributed along the width of the chamber  100  in the lateral direction  120 , such that they are on either side of the substrate  108 , which enhances the uniform delivery of the cooling gas through the chamber  100 . Likewise, the same arrangement can be made for the gas outlet ports  110  on the second sidewall section  112   b  of the chamber  100  in relation to the substrate  108 . 
       FIG. 3  shows another exemplary arrangement of multiple gas inlet ports  104  on the first sidewall section  112   a  of the integrated load lock chamber of  FIGS. 1 a  and  b   , according to some embodiments of the present invention. As shown, an equal number of inlet ports  104  are arranged above and below the substrate  108  in the vertical direction  118  to ensure uniform cooling of the top and bottom surfaces  108   a ,  108   b  of the substrate  108  in the holder  106 . These ports  104  can be offset relative to each other above and below the substrate  108 . Likewise, the same arrangement can be made for the gas outlet ports  110  on the second sidewall section  112   b  of the chamber  100  in relation to the substrate  108 . 
       FIG. 4  shows an exemplary arrangement of at least one outlet port  110  on the second sidewall section  112   b  of the load lock chamber  100  of  FIGS. 1 a  and  b   , according to some embodiments of the present invention. As shown, one gas outlet port  110  is located on the second sidewall section  112   b  of the chamber  100  positioned at substantially the same height along the vertical direction  118  as the substrate  108  in the chamber  100 . The gas outlet port  110  has a wide opening along the lateral direction  120  through which the substrate  108  can be loaded into and unloaded from the interior of the chamber  100 . Thus, the gas outlet port  110  can provide the dual function of conducting the cooling gas out of the chamber  100  as well as enabling the loading and unloading of the substrate  108  relative to the chamber  100 . 
       FIG. 5  shows another exemplary arrangement of multiple outlet ports  110  on the second sidewall section  112   b  of the load lock chamber  100  of  FIGS. 1 a  and  b   , according to some embodiments of the present invention. As shown, multiple gas outlet ports  110  are aligned with the substrate  108  in the vertical direction  118 , such as at about the same vertical height as the substrate  108  in the chamber  100 . The gas outlet ports  110  are also evenly distributed along the width of the chamber  100  in the lateral direction  120 , such that they are on either side of the substrate  108 , thereby enhancing the uniform delivery of the cooling gas through the chamber  100 . Likewise, the same arrangement can be made for the gas inlet ports  104  on the first sidewall section  112   a  of the chamber  100 . In general, any reasonable arrangement of the inlet ports  104  and/or the outlet ports  110  are within the scope of the present invention to provide uniform gas flow across the top and bottom surfaces  108   a ,  108   b  of the substrate  108 . Due to the small opening of each gas outlet port  110  in this exemplary configuration, a separate opening (not shown) may be disposed on another sidewall section of the load lock chamber  100  for receiving and removing the substrate  108 . 
     In another aspect, the present invention features various mechanisms for securing the substrate  108  to the load lock chamber  100 . In cases where the cooling gas flow across the substrate  108  has a high velocity, the cooling gas flow can potentially disturb and move the substrate  108 . Therefore, it may be desirable to secure the substrate  108  within the chamber  100  to prevent substrate movement. However, when the velocity of the cooling gas is low, the substrate  108  is unlikely to move, thus may not need to be secured. 
       FIG. 6  shows an exemplary mechanism for preventing movement of the substrate  108  in the load lock chamber  100  of  FIGS. 1 a  and  b   , according to some embodiments of the present invention. As shown, the substrate  108  is positioned on at least one pad  402  coupled to the holder  106  in the load lock chamber  100 . The pad  402  has one or more bumpers  404 , such as side walls, that are raised in the vertical direction  118  to limit a lateral sliding movement of the substrate  108  caused by, for example, the cooling gas flowing along the lateral direction  120 . Thus one or more of the pad-bumper combination can be distributed around the edge/perimeter of the substrate  108  to hold the substrate  108  in place relative to the holder  106 . A bumper  404  can be integrated with the pad  402  or removably attached to the pad  402 . 
       FIG. 7  shows another exemplary mechanism for preventing movement of the substrate  108  in the load lock chamber  100  of  FIGS. 1 a  and  b   , according to some embodiments of the present invention. In some instances, the cooling gas flow is sufficiently fast to generate a lifting force in the vertical direction  118 , which can cause the substrate  108  to jump over the bumpers  404 . To prevent such lifting movement of the substrate  108  while it is positioned on the pad-bumper combination  402  and  404 , a clamping mechanism is used to apply a vertical force to the top surface  108   a  of the substrate  108  to counteract any lifting motion by the cooling gas flow. As shown in  FIG. 7 , a clamping pin  502  is coupled to the top wall  114  of the load lock chamber  100  and substantially aligned with a corresponding pad  402  on the holder  106 . Thus, a clamping pin  502  can be used for each pad  402 . The tip  504  of the clamping pin  502  is adapted to contact the top surface  108   a  of the substrate  108  to exert a physical pressure on the substrate  108  in the vertical direction  118  against the pad  402 , thereby preventing at least one of lateral or vertical movement of the substrate  108 . In some embodiments, the pressure asserted by the clamping pin  502  prevents both lateral and vertical movement of the substrate  108 . In some embodiments, the tip  504  of the clamping pin  502  is adapted to make contact with the top surface  108   a  of the substrate  108  at a certain tolerance distance from the edge of the substrate  108 , such as at a distance of about 2 mm from the edge of the substrate  108 . The clamping pin  502  does not need to be used in conjunction with the bumper  404 . In some embodiments, only one or more clamping pins  502  and pads  402  are used without the pads  402  being attached to the bumpers  404 . 
     In some embodiments, the clamping pin  502  is attached to an actuator  600 .  FIG. 8  shows a retractable actuator  600  as an example of the clamping mechanism of  FIG. 7  for preventing movement of the substrate  108  in the load lock chamber  100  of  FIGS. 1 a  and  b   , according to some embodiments of the present invention. As shown, the actuator  600  includes a top portion  602  and a set of bellows  604 . The clamping pin  502  includes a rod portion  605  and a tip  606  held in the rod portion  605  by a retention spring  608 . In operation, air pressure is applied to the top portion  602  of the actuator  600  to compress the set of bellows  604 , which pushes the rod portion  605  of the clamping pin  502  along with the tip  606  downward in the vertical direction  118  against the top surface  108   a  of the substrate  108 . Once the air pressure is released, the rod portion  605  (along with the tip  606 ) of the clamping pin  502  is adapted to retract upward to release the pressure against the substrate  108 . The tip  606  of the clamping pin  502  can also be replaceable. Using such a retractable actuator  600  is advantageous because an operator can choose to activate the actuator  600  to reinforce the positioning of the substrate  108  within the chamber  100  only when the cooling gas flow is fast and/or the bumper  404  is not sufficient to prevent the substrate  108  from moving. The actuator  600  can cause the clamping pin  502  to be in its retracted position when such additional securement is not needed. 
       FIG. 9  shows yet another exemplary mechanism for preventing movement of the substrate  108  in the load lock chamber  100  of  FIGS. 1 a  and  b   , according to some embodiments of the present invention. As shown, a second flow of fluid, in addition to the lateral cooling gas flow, is provided to the load lock chamber  100  to prevent movement of the substrate  108  within the chamber  100 . The vertical fluid flow can be introduced into the chamber  100  from at least one inlet port  702  located on the top wall  114  of the chamber  100 . The inlet port  702  is configured to deliver the second fluid flow in the vertical direction  118 , thereby exerting a vertical pressure on the top surface  118   a  the substrate  118  to prevent the substrate  118  from moving laterally or vertically due to, for example, the lateral gas flow introduced from the one or more gas inlet ports  104 . The second fluid introduced from the inlet port  702  can be a cooling gas the same as or different from the lateral cooling gas flow from the inlet port  104 . The second fluid does not need to be a cooling gas. It can be any reasonable fluid for the purpose of keeping the substrate  100  in place inside of the chamber  100 . The vertical fluid flow approach can be employed in conjunction with one or more of the mechanisms described above with respect to  FIGS. 6-8  to stabilize the substrate  108 . Alternatively, the vertical fluid flow approach can be employed as a stand-alone mechanism for stabilizing the substrate  108  inside of the chamber  100 . 
       FIG. 10  shows an exemplary process  800  for cooling a substrate inside of the load lock chamber  100  of  FIGS. 1 a  and 1 b   , according to some embodiments of the present invention. At step  802 , the substrate  108  is secured to the holder  106  in the chamber  100  using one or more of the securing mechanisms explained above with reference to  FIGS. 6-9 . For example, the substrate  108  can be positioned on one or more pads  402  that are coupled to the holder  106 . In some embodiments, the pads  402  are attached to one or more bumpers  404  to prevent the substrate  108  from moving laterally within the chamber, as illustrated in  FIG. 6 . In some embodiments, a clamping pin  502 , as attached to a retractable actuator  600 , is used to restrain the substrate  108  in the vertical and/or lateral directions  118 ,  120 , as illustrated in  FIGS. 7 and 8 . In some embodiments, a vertical fluid flow is used to restrain the substrate  108  in the vertical and/or lateral directions  118 ,  120 , as illustrated in  FIG. 9 . 
     At step  804 , a cooling gas, such as nitrogen gas, is introduced into the chamber  100  via at least one gas inlet port  104  that is configured to conduct the gas in the lateral direction  120  substantially parallel to the top and bottom surfaces  108   a ,  108   b  of the substrate  108 . The gas inlet port  104  is located on the first side wall section  112   a  of the chamber  100 . In some embodiments, an operator can manipulate one or more valves coupled to the gas inlet port  104  to achieve a variable flow rate of the cooling gas. In some embodiments, the flow rate of the cooling gas is adjusted to create laminar or turbulent flow conditions. 
     At step  806 , the cooling gas is adapted to exit from the chamber  100  via at least one gas outlet port  110  along the lateral direction  120 . The gas outlet port  110  is located on a second side wall section  112   b  of the chamber  100  substantially opposite of the first side wall section  112   a  of the chamber  100  with the substrate  108  disposed therebetween. 
     Such lateral flow of the cooling gas from the inlet port  104  to the outlet port  110  is adapted to cool both the top and bottom surfaces  108   a ,  108   b  of the substrate  108  at step  808 . Specifically, the gas inlet port  104  and/or the gas outlet port  110  are positioned on their respective side wall sections  112  to allow substantially uniform flow of the cooling gas across the top and bottom surfaces  108   a ,  108   b  of the substrate  108 . For example, at least one of the gas inlet port  104  or the gas outlet port  110  can be positioned along its corresponding side wall section at about the same vertical height as the substrate  108  in chamber  100 . 
     One skilled in the art will realize the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting of the invention described herein. Scope of the invention is thus indicated by the appended claims, rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.