Abstract:
A load lock and related method of handling a substrate involves placing a substrate onto a vertically movable poppet and moving the poppet between two vertically opposed subchambers such that in moving the poppet toward one of the subchambers, that subchamber is sealed to atmosphere. The two subchamber system allows one substrate to be placed into a buffer and another substrate to be cooled at the same time. Also, the system allows for a slow vacuum to be made on the substrate in a subchamber to avoid undesirably loading the substrate by the otherwise immediate drop in pressure.

Description:
BACKGROUND OF THE INVENTION 
     This application is based upon copending provisional application Ser. No. 60/055,329 filed on Aug. 12, 1997, on which application priority of the present application is based. 
    
    
     FIELD OF THE INVENTION 
     The apparatus of the present invention relates generally to material transfer devices and more particularly to an improved method and article of handling substrates within a substrate transport. 
     The material transferred might include, but not be limited to, semiconductor wafers, such as silicone and gallium arsenide, semiconductor packaging substrates, such as high density interconnects, semiconductor manufacturing processing imaging plates, such as masks or reticles, and large area displayed panels, such as active matrix LCD substrates. 
     The need for high throughput transport devices which can move a substrate or workpiece between remote locations within a highly confined footprint such as found in the manufacture of wafers or panels or the like used in the semiconductor industry is in high demand. This is because in the process of manufacturing such panels, wafers or the like, the need to move a workpiece from one position to the next not only requires that a high throughput rate be achieved, but also that maximum throughput between component elements of the tool is achieved. In this way, processing time for a given number of substrates can be maximized for a given tool. 
     Copending U.S. patent application Ser. No. 08/654,334 filed in the name of Hendrickson, filed on May 28, 1996 and entitled A System for Heating or Cooling Wafers and U.S. Pat. No. 5,588,827 entitled A Passive Gas Substrate Thermoconditioning Apparatus and Method, issued on Dec. 31, 1996 to Richard Muka, disclose a substrate transport having a main vacuum transport chamber to which a temperature transfer station is mounted. Thus, it is known in the art to connect an individual substrate thermoconditioning module to a side of the substrate transport outside of the main transport chamber. Also, in copending U.S. patent application Ser. No. 08/891,532 filed under Express Mail No. EM029241165 US and entitled A Substrate Processing Apparatus Having A Substrate Transport with a Front End Extension and an Internal Substrate Buffer, filed on Jul. 11, 1997 in the name of David Beaulie and Michael W. Pippins, now U.S. Pat. No. 5,882,413, discloses a method and apparatus for forming an integrated platform in which a wafer cooler is provided. However, the device disclosed in this patent application has an extended footprint as it uses separate elements, namely, a cooler  36 , a buffer, and load locks to effect three different functions for the three separate elements. However, the fabrication and usage of the three elements occupies much needed additional footprint space which otherwise could be used for other process modules and/or cluster tools in the substrate fabrication process. 
     Accordingly, it is an object of the invention to provide a single substrate load lock with offset cool module and buffer chamber which is capable of transporting substrates from an external environment to a vacuum environment for processing and then back to a factory interface in a manner such that no damage occurs due to thermal shock or nonuniformity in the substrate. 
     Another object of the invention is to provide a substrate load lock of the aforementioned type wherein the cost of fabrication is reduced by efficiency of the design and construction. 
     Still a further object of the invention is to provide a substrate load lock of the aforementioned type which is reduced in complexity of drive mechanisms and controls. 
     It is still a further object of the invention to provide substrate load lock of the aforementioned type which reduces vacuum volume thereby reducing the amount of pumping capability required to maintain adequate vacuum in the system. 
     Yet still a further object of the invention is to provide a substrate load lock of the aforementioned type wherein the manufacturing time, complexity of construction, alignment in time testing are reduced. 
     Further still an object of the invention is to provide a substrate load lock of the aforementioned type wherein service and reliability as well as reduced system time throughput are enhanced. 
     SUMMARY OF THE INVENTION 
     The invention resides in the single substrate load lock with offset cool module and buffer chambers. The load lock is provided as an interface to a substrate handling transport system via a vacuum isolation slot valve. The load lock allows for a single substrate transition from an external environment to the vacuum environment of the transport chamber while a second substrate may reside either in the buffer chamber or the cooling chamber. In either case, with or without a substrate in the buffer or cooling chambers, the load lock is adapted and is configured to provide a throughput mode wherein a substrate is loaded into the load lock from the outside without interfering with a substrate placed either in the buffer chamber or in the cooling chamber. 
     The invention further relates to a method of handling a substrate in a cluster tool wherein a load lock with a cool down chamber and a buffer chamber is provided and is in selective vacuum communication with a transfer chamber associated with one valve and a second valve associated with an external environment. Thus, the system provides a reduced impact from vacuum to substrates as each is exposed to vacuum when moved from an external environment and vice versa. It is preferred to open the external valve to the external environment only when a substrate is sealed within one of the subchambers by either upward or downward movement of the poppet. In other words, the load lock configuration allows for fast venting only of empty areas where no substrate is disposed, but venting in the sealed subchambers is, rough or staggered, thus avoiding shocking the substrate. 
     More specifically, the invention resides in a typical sequence whereby a processed substrate is moved into the load lock and onto the holding members of the poppet, the poppet is lowered into subchamber and interior valve is closed. Fast evacuation of the main chamber and subchamber (empty) next begins. Next, cooling in a subchamber may take place. The external environment valve is opened and a new substrate is placed onto the poppet. The poppet is raised. Slow rough evacuation of the subchamber with the new substrate held therein is accomplished. Removal of cooled substrate from the poppet next occurs. The external environment valve is next closed. Fast evacuation of all chambers occurs and the internal valve is opened. The transport apparatus places a processed substrate onto the poppet. The poppet is next lowered. The transport apparatus may pick or place another substrate from the poppet if appropriate, and the internal valve is closed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top plan view of a substrate processing apparatus shown schematically incorporating the features of the present invention. 
     FIG. 2 is a perspective view of the main section of the apparatus shown in FIG.  1 . 
     FIG. 3 is a partial fragmentary vertical section taken through the load lock of the present invention showing the substrate platen in its down position. 
     FIG. 4 is a partially fragmentary vertical section taken through the load lock of the invention showing the substrate poppet in its vertically up condition. 
     FIG. 5 is a bottom view of the poppet. 
     FIGS. 6 a  and  6   b  when combined are a flow chart of one scheme which is capable of being employed by the load lock of the invention. 
     FIGS. 7 a - 7   d  show schematically various stages of the poppet support during one process of the invention. 
     FIG. 8 is an alternate embodiment of a partial fragmentary vertical section taken through the load lock of the present invention showing the substrate platen in its down position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, there is shown a schematic top plan view of a substrate processing apparatus  10  incorporating features, of the present invention. Although the present invention will be described with reference to the single embodiment shown in the drawings, it should be understood that the present invention can be embodied in many alternate forms of embodiments. In addition, any suitable size, shape or type of elements or materials could be used. 
     The apparatus  10  includes a main section  12 , substrate processing modules  14 , substrate load lock modules  16 , and an external environment  17 . The environment  17  may include means for holding cassettes of substrates and a robot (not shown) for moving the substrates into and out of the load locks  16 . In alternate embodiments, any suitable substrate loading system, manual and/or automatic computer controlled, could be used for loading substrates into the load locks  16 . 
     Referring also to FIG. 2, a perspective view of the main section  12  is shown. The cover  24  is shown in an up position for illustration purposes. During normal operation, the cover  24  is closed and sealed on top of the frame  18 . The main section  12  is a substrate transport having a housing  13  and a substrate transport mechanism  22 . The housing  13  has a frame  18  with multiple side apertures having door sections  20 , 20 ′. The modules  14 ,  16  are connected to the door sections  20 , 20 ′. The door sections  20  have doorways  21  with movable door mechanisms or valves to open and close the doorways. The substrate processing modules  14  and the load lock modules  16  are well known in the art. The substrates S could be semi-conductor wafers, flat panel display substrates, or any other type of substrate. The substrate transport mechanism  22  is provided for moving the substrates S among the modules  14 ,  16 . 
     The substrate transport mechanism  22  has a drive section  25 , a movable arm section  27  and two substrate holders  29 . The holders  29  can be moved through the doorways  21  into and out of the modules  14 ,  16  to move the substrate S into and out of the modules  14 ,  16 . A similar substrate transport mechanism is described PCT patent publication No. WO 94/23911 (corresponds to U.S. Pat. No. 5,720,590) which is hereby incorporated by reference in its entirety. However, any suitable type of substrate transport mechanism can be used. The housing  13  includes the movable top cover  24  and a cover movement crank  26 . The front end  28  of the housing  13  has one or more load locks  16 ,  16 . The term “front end” is used merely for descriptive purposes. The extended section could be located on any side of the housing, could be spaced from paths to and from the load locks, and/or could comprise multiple extended sections. Depending on the application, see copending U.S. Applications Ser. Nos. 60/055,332 (provisional of) 09/084,754 filed concurrently herewith and entitled, A Dual Plate Gas Assisted Degas Module, herein incorporated by reference, one of the modules  14  could be defined by the structure disclosed therein, while the load lock(s) may be defined by the structure of the present application. Thus, the substrate handler load locks  16 ,  16  and the modules  14  could include a substrate degas/pre-heater, a combined substrate heater/cooler, cooler or heater/cooler, or any other suitable type of substrate handler. 
     The load locks  16 ,  16  connect directly to the housing  13  so as to extend outwardly at an angle so as to allow the nearby substrate processing modules  14  to be angled and positioned as shown. This helps to orientate all of the substrate processing modules at efficient locations and spacings with the main section  12 . The front section  28  being defined by load locks  16 , 16 , is comprised of separate pieces removably connected to the rest of the frame  18 , or alternatively could be formed integrally with the front end of the housing  12 . What is desired is that the front section as defined by one or more of the load locks  16 , 16  have a chamber(s) which are in selective vacuum communication with the main chamber  31 . The general length D as measured from the substrate load lock center C in each load lock  16 ,  16  to the axis A of rotation of the transport mechanism  22  of the front extended section  30  is sufficiently short to allow the movable arm section  27  of the transport mechanism  22  to pass through the valves  20 ′, 20 ′ associated with the front section of the housing  13  and into the load locks  16 , 16 . The housing  13  forms a main transport chamber  31  therein. 
     The main transport chamber  31  has the movable arm section  27  therein and the doorways  21  are located at the outer perimeter of the chamber  31 . The chamber  31  is maintained as a substantially closed environment. The valves  20 , 20 ′ at the doorways  21  can be temporarily opened for inserting and removing substrates with the modules  14 ,  16 . Preferably, the main chamber  31  is maintained in a vacuum. However, the main chamber  31  could alternatively be filled with an inert gas. 
     Referring now to FIGS. 3 and 4, and in particular to the load lock  16 , 16  of the invention, it should be seen that the load locks  16  are provided with two valves, the first of which as discussed previously is valve  20 ′ which is disposed intermediate the internal chamber  31  of the transport mechanism  22  and an internal chamber  50  of the load lock. Opposite the valve  20 ′ is a similar valve  52  which is associated with the external environment  17  and an aperture  19  in the load lock. A like aperture  19 ′ exists at the other end of the load lock adjacent the valve  20 ′. 
     Vertically movably disposed within the chamber  50  of the load lock  16  is a generally circular planar support member or poppet  54  having upstanding standoffs  56  for mounting a substrate thereon. Opposite sides of the poppet  54  are connected respectively with two vertically movable rods  58 , 58  which are connected to one another via a horizontally disposed transverse bar  60  which is in turn moved by an actuator  62  secured to a cantilevered post member  64  which is mounted to the top of the load lock  16 . Depending from the poppet  54  are a plurality of inwardly directed holding pins  66 , 66  with depending portions  68  fixedly secured to the undersurface of the poppet  54 . Referring for the moment to FIG. 5, it should be seen that the depending portions  68 , 68  of the holding pins  66  are located laterally outwardly beyond the width W of the doorway/port  19 ′, 21  associated with the valve  20 ′ such that the substrate S passes freely through and into the chamber  50  without interference from the depending portions  68  when the poppet  54  is in the upwardly raised condition. 
     The chamber  50  of the load lock  16  is defined by two working subchambers. The first of which subchambers is defined by an upper buffer chamber  70  located at the top portion of the chamber  50  and a lower thermal chamber  72 . Each of the subchambers  70  and  72  is defined by a circular opening  74 ,  76  respectively, in communication with the chamber  50 . Disposed about each of the openings  74  and  76  is an annular gasket  80 , 80  which is capable of sealing each of the subchambers in the manner which will be discussed in greater detail later. As is illustrated in the drawings, the diameter of the circular poppet  54  is greater than the diameter of the openings  74  and  76  formed in the housing of the load lock  16 . Thus, as the poppet  54  is moved between vertical up and vertical down positions as shown respectively in FIGS. 4 and 3, the force applied in each such direction by the actuator  62  is sufficient to cause sealing by one of the corresponding upper and lower surfaces of the poppet  54  with a juxtaposed one of the annular gaskets  80 , 80  fixed to the load lock housing about each of the openings  74  and  76 . As such, it should be understood that each of the subchambers  70  and  72  is capable of being sealed relative to the remainder of the chamber  50  by virtue of the vertical movement of the poppet  54 . In other words, the movement of the poppet  54  between vertically up and down positions causes the poppet to behave like an isolation valve between the two subchambers  70  and  72 . 
     Communicating with both the lower subchamber  72  and the upper subchamber  70  is a vacuum pump  82  which is responsible for evacuating the entire chamber  50  or only one of the subchambers  70 ,  72 . The vacuum pump  82  is connected to both subchambers  70  and  72  through a rough out valve  84 . The base of the subchamber  70  is provided with a cooling plate  92  disposed therein. The cooling plate  92  is connected to a heat transfer device and is responsible for drawings off heat from substrates which require cool down prior to being transferred out of the load lock and to the external environment or require cool down before entering another processing step within the apparatus  10 . 
     In operation, the subchamber  70  would serve as a buffer station for a single substrate to reside in vacuum while a second substrate is either loaded from the external environment or is moved from the internal confines of the chamber  31  and placed onto the holders  66  which depend from the poppet  54 . It is a further feature of the invention to provide vacuum in selective communication with the subchambers  70  and  72  for evacuating air from one such subchamber while leaving the other such subchamber open to the external environment. Thus, for example, once the poppet is raised to its vertically closed condition, such as in the example where a substrate is loaded from the external environment through the valve  52  and onto the depending holding members  66 , 66 , the upper subchamber  70  may remain in vacuum with the remainder of the chamber  50  being exposed to a different pressure. Conversely, if desired, the poppet may be moved to its vertical down condition thereby sealing the lower subchamber  72  and allowing the remainder of the chamber  50  to be exposed to the external environment. Thus, when the poppet is raised to its upward condition, the subchamber  70  can be independently evacuated and when the poppet is lowered, the subchamber  72  can be independently evacuated. During such modes of operation where the external environment valve  52  is opened, it is understood that the valve  20 ′ is in its closed condition barring the exposure of the main chamber  31  to the external environment. 
     It is a feature of the invention to provide a reduced impact from vacuum to substrates as each is exposed to vacuum from the external environment and vice versa. Thus, it is preferred to open the external valve  52  to the external environment only when a substrate is sealed within one of the subchambers  70 ,  72  by either upward or downward movement of the poppet. 
     In other words, the load lock configuration of the present invention allows for fast venting only of areas of the chamber  50  in which no substrate is disposed, but in the sealed subchambers, only rough or staggered occurs, thus avoiding shocking the substrate. 
     A typical sequence would be as set forth in the flow diagram of FIGS. 6 a  and  6   b.    
     A processed substrate is moved into the load lock  16  from the main chamber  31  and is placed onto the depending holding members  66 , the poppet is lowered into subchamber  72  and interior valve  20 ′ is closed. (step  100 ) 
     Cooling begins, see FIG. 7 a . (step  102 ) 
     Close internal valve  20 ′. (step  104 ) 
     Fast venting of chamber  50  and subchamber  70  (empty) begins. (step  106 ) 
     External environment valve  52  is opened. (step  108 ) 
     Place new substrate onto stand offs  56 , see FIG. 7 b . (step  110 ) 
     Slow vent lower chamber. (step  112 ) 
     Raise poppet  54  and slow rough evacuation of subchamber  70  with new substrate held therein. (step  114 ) 
     Remove cooled substrate from poppet through valve  52 . (step  116 ) 
     Close atmospheric valve  52 . (step  118 ) 
     Fast evacuation of remaining chambers  50 ,  70 , and  72 , see FIG. 7 c . (step  120 ) 
     Open internal valve  20 ′. (step  122 ) 
     Transport apparatus places processed substrate onto poppet depending members  66 , see FIG. 7 d . (step  124 ) 
     Lower poppet. (step  126 ) 
     Transport apparatus picks substrate from top of poppet. (step  128 ) 
     Close internal valve  21 ′. (step  130 ) 
     The cooled substrate may be returned to the main processing chamber or may exit the load lock. (step  132 ). 
     Thus, the substrate is normally placed onto the platen in the condition shown in FIG. 4 by opening the outside valve  52  to the external environment and maintaining the valve  20 ′ closed to the inner chamber  31  of the transport apparatus. All the while, it should be understood that while loading a substrate from the external environment through the valve  52  it is entirely possible and desirable to maintain a substrate within the upper chamber  70  in a buffer condition. As seen from the above example, such a substrate in the buffer condition in the subchamber  70  could be transported into the chamber  50  of the load lock  16  with the outside valve  52  closed to the external environment and inside valve  20 ′ open to the main chamber  31  of the transport apparatus. In this case, the transport apparatus  22  would move a substrate into the load lock with the poppet in the lowered condition as shown in FIG.  3  and thereafter the poppet can be raised with the substrate placed into a buffer condition. Since the load lock  50  would already be in vacuum, there is no reason to provide vacuum to the subchamber  70  in this scenario. 
     Assuming a substrate is located in the upper subchamber  70  in a buffer condition and the valve  20 ′ to the main transport chamber is closed and with the outer valve  52  open to the external environment, a substrate can thus be taken out of the load lock from the poppet and if no substrate is to be loaded, the holding members  66  are left empty. Thereafter, the outer chamber valve  52  is closed to the external environment and vacuum applied to the chamber  50  through the vacuum valve  84  in a manner discussed above. With the chamber  50  brought down to vacuum, the inner valve  20 ′ may be open. At this point it may be possible to use the transport apparatus  22  to move a substrate into the load lock chamber  50 , if there is no substrate present. 
     Depending on the application, it is a feature of the invention to allow the substrate in the buffer subchamber  70  to be lowered through the intermediary of the actuator  62  such that it can be picked up and moved by the substrate holder  29 . Alternatively, it is well within the purview of the invention to maintain the substrate previously moved to the buffer subchamber  70  or the lower chamber  72  within that-chamber and have the more currently loaded substrate from the apparatus  22  maintained on the last open holders of the poppet. 
     Another aspect of the invention is provided by the cooling plate  92  located in the lower subchamber  72 . The cooling plate  72  provides passive cooling to substrates held on the lower holders  66 . Thus, with two such load locks  16 , 16  as shown in FIG. 1, two cooling cycles are provided by the system. In each cooling cycle, a substrate which has been worked in is moved into the load lock  16  from within the main chamber  31 . At this point, the substrate having been processed through one of the process modules  14 , 14  is very hot and must be cooled prior to making the transition through to the factory interface or back into the main transport chamber  30 . This is important because after such processing occurs, the substrate temperatures are elevated to several hundred degrees centigrade. The temperature must be reduced in a controlled manner so that no damage occurs due to thermal shock or nonuniformity. 
     Thus, with substrate held on the depending holders  66 , cooling may be effected. Such cooling may occur simply by lowering the substrate into the lower subchamber  72  so that it is in close proximity with the cooling plate  92 . Once the cooling process is complete, the poppet can be raised, assuming chamber  50  is in vacuum, to allow access of the cooled substrate by the handling interface occurring through the then opened valve  52 . It should be understood, another important feature of the invention is that during the cooling process which requires the substrate held on the depending holders  66 , the chamber  50  can be functional, although not preferred, as a pass through load lock for moving a substrate between the external environment interface outside the valve  52  and the inner main chamber  31  of the transport apparatus. 
     As illustrated in FIG. 8, one or both of the load locks  16 , 16  can be modified to include a heating element  99  which is provided within subchamber  70  for heating of the substrate prior to entering a given one of the processing modules  14 , 14 . Thus, with such a load lock, numerous options are available to a system employing such a device(s) given that both heating (within chamber  70 ) and cooling (within chamber  72 ) are made possible on different substrates within the same load lock. For example, a new substrate could be loaded into the load lock through exterior valve  52  and onto the elements  56  of the poppet  54 . The poppet could then be moved upwards into chamber  70  where slow evacuation and heating takes place. In the meantime, the exterior valve  52  would be closed, the remaining chamber(s) fast evacuated, and the interior valve opened. A processed substrate could be loaded onto the holding members  66  of the raised poppet and then lowered. The heated substrate on the top elements  56  could then be moved off and into the central processing chamber and the cycle would continue much in the same way as explained above with reference to FIGS. 6 a  and  6   b.    
     By the foregoing an improved single substrate load lock with offset cool module and buffer chamber has been described by way of the aforementioned description. However numerous substitutions and modifications may be had without departing from the spirit of the invention. For example, the upper subchamber  70  or buffer chamber is ideally suited for handling and storing a dummy/cleaning substrate which could be used in the cleaning operation for each of the process modules. Preferably each cleaning operation substrate is only used with one of the modules  14 . However, a single dummy/cleaning substrate could also be used to clean multiple processing modules. A cleaning substrate could be maintained a top the standoffs  56 , 56  and held there until such time a cleaning operation was designated for one of the process modules.