Abstract:
A linear substrate delivery and load lock system including a vacuum transfer chamber having a slit valve connected to a processing chamber and a rotatable carousel having two or more seats for supporting substrates in split path between the substrate source and the processing chamber. Two linear transfer mechanisms transfer the substrates between the source and the carousel and between the carousel and the processing chamber. The transfer mechanism may be disposed mostly located below the carousel and have similar structures but with arms having substrate blades on their end extending in opposite directions to move between the carousel and the source and processing chamber respectively. The carousel moves vertically to effect the transfer to and from the blades. A vertically movable cassette may constitute the substrate source.

Description:
RELATED APPLICATION  
       [0001]     This application claims benefit of provisional application 60/679,048, filed May 9, 2005. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates generally to substrate handing systems. In particular, the invention relates to substrate handling systems involving linear motion from a load lock to a vacuum processing chamber.  
       BACKGROUND ART  
       [0003]     The fabrication of semiconductor integrated circuits is one of several technologies involving the use of vacuum processing chambers for processing wafers or other substrates in a high vacuum, often using noxious or explosive gases or with plasmas or operating at very high temperatures. Typical chamber pressures for deposition and etching steps range from around a few to many torr for chemical vapor deposition to a millitorr and below for sputtering. Etching pressures typically are intermediate. Establishing very low pressures requires a long pump down from atmospheric pressure and possibly heating of the chamber surfaces to remove adsorbed gases. The pump down problem is exacerbated by the trend toward single-wafer processing reactors in which only a single wafer is processed at a time in the reactor. Some of the processing gases are explosive, such as hydrogen, and should be strictly isolated from ambient oxygen.  
         [0004]     Both in a production environment and even in research, it has become common practice to maintain the pressure within the processing reactor chamber at a pressure close to the processing pressure even while a substrate is being transferred into or out of the processing reactor chamber. High-volume semiconductor fabrication lines rely largely on platforms or integrated tools having a central transfer chamber around which are arranged several processing chambers and which is pumped to a reduced pressure. Slit valves are formed on the walls of the transfer chamber and selectively separate the transfer chamber from multiple processing chambers and from a load lock through which wafers are loaded into the system from cassettes originally held at atmospheric pressure. Each of the vacuum-isolated processing chambers, the transfer chamber, and the load lock is independently vacuum pumped. A robot located in the transfer chamber is driven by one or more shafts extending along the central axis of the transfer chamber and is connected to them through magnetic coupling or other types of vacuum feedthroughs. The robot controls a wafer paddle through a frog-leg or other mechanism which can both rotate around the central axis and move into any of the processing chambers or the load lock. Thereby, wafers are passed through the selectively opened slit valves and the transfer chamber as they are transferred between the load lock and the processing chambers. Such a system allows the rapid transfer of wafers between chambers in which processing times for a single step are typically less than a minute.  
         [0005]     However, such an integrated tool is not always appropriate. The central transfer chamber is large, and it and the robot are expensive. Many applications, particularly those involving research and development but also those involving low-volume production of high-value circuits, do not require the high throughput or multiple processing chambers available in integrated tools but these application still benefit from a load lock. Production of some components, such as optical circuits and MEMS (micro electromechanical systems), fabricated in silicon-on-insulator (SOI) substrates may require processing times on the order of hours, and such substrates are often processed in relatively small numbers. Photomask reticles used in optical lithographically may in part be produced by semiconductor processing equipment. These reticles typically are square panes of glass having dimensions of approximately 150 mm×110 mm on which metal mask layers are deposited, defined, and cleaned. These high-value items are produced in relatively small quantities. Much larger glass panels are used in the fabrication of flat panel displays. A low-cost load-lock system would be useful in the development phase.  
         [0006]     Accordingly, several single-wafer load lock and wafer delivery systems have been proposed. It is understood that such wafer delivery systems can be applied with very little change to rectangular substrates so that the term wafer as used hereafter will include other shapes of substrates. The present inventors have disclosed a magnetically coupled linear substrate delivery system in U.S. Pat. No. 6,935,828, incorporated herein by reference in its entirety. This system relies upon a single wafer paddle (effector) traveling along a single track and magnetically coupled to an external drive to transfer a wafer from an input side of a vacuum pumped transfer chamber into a processing chamber on the opposed processing side of the transfer chamber. In one embodiment, individual wafers are manually placed into the transfer chamber, which is then pumped down to a pressure close to that of the processing chamber. Thereafter, a slit valve between the transfer and processing chambers is opened and the transfer mechanism places the wafer on a pedestal in the processing chamber. The paddle withdraws, the slit valve is closed, and the wafer is subject to the desired processing. After processing, the procedure is reversed. The processed wafer is manually removed from the transfer chamber and a new wafer is inserted. In another embodiment, an entire cassette is placed in or adjacent to the transfer chamber and the chamber is pumped down. The linear transfer mechanism removes one wafer from the cassette with one end of the paddle, withdraws it, and places it upon a raisable pedestal in the transfer chamber. The paddle moves back, and the wafer is then transferred from the pedestal onto the other end of the paddle. The transfer mechanism then moves the paddle and supported wafer into the processing chamber. After processing, the processed wafer is returned to the cassette. The cassette is then vertically moved to position a fresh wafer in alignment to the paddle, and the process is repeated for all wafers in the cassette.  
         [0007]     The cassette embodiment offers clear advantages in even low-volume production environments with the infrequent need to pump the transfer chamber between atmospheric and processing pressures. However, the single path between the cassette and processing chamber presents a bottle neck as the processed and unprocessed wafers are transferred between the cassette and the processing chamber along a single path. In some circumstances, the single path severely impacts throughput of the expensive processing chamber because of required cooling time after processing. For example, SOI wafers may need to be annealed at 1300° C. The paddles may be designed to transfer a hot wafer, but the commercially important FOUP cassettes are composed of a plastic material so that it is required to let the wafer cool almost to room temperature before it is placed in the cassette. Only after the cooling period can an unprocessed wafer be moved from the cassette to the processing chamber. During the cooling period, the processing chamber is inactive. Even in processes not requiring cool down, the entire sequence of motions performed by the transfer mechanism, the pedestal elevator, and the pedestal actuator for two different wafer are performed with the processing chamber left empty, thereby reducing processing throughput.  
         [0008]     Simplified versions of the production transfer chambers having a central rotating robot have been proposed for use with only a single processing chamber and a cassette load lock arranged around the robot. Although effective, the apparatus are expensive and occupy a large amount of valuable fab floor area.  
       SUMMARY OF THE INVENTION  
       [0009]     A linearly operating substrate transfer system in which a rotatable carousel can support multiple substrates. Two linear transfer mechanism transfer substrates between the carousel and a processing chamber and another location, such as a substrate cassette.  
         [0010]     The transfer mechanism, in one set of embodiments, moves beneath the carousel with its motive sources generally located therebelow. Arms of the transfer mechanisms are projectable from the carousel to the source and process sides respectively.  
         [0011]     The two transfer mechanisms may have substantially the same form and be aligned side by side but operate in opposed horizontal directions.  
         [0012]     The carousel may be both rotatable and vertically movable to engage the paddles of the transfer mechanisms, which may be held to the same plane. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a schematic cross-sectional view of a first embodiment of a substrate transfer system of the invention including a vacuum sealable door for inserting a substrate cassette into the transfer chamber.  
         [0014]      FIG. 2  is a schematic cross-sectional view of a second embodiment of the invention including a slit valve on the source side of the transfer chamber opening to atmosphere.  
         [0015]      FIG. 3  is a schematic cross-section view of a third embodiment of the invention including a slit valve on the source side of the opening to a vacuum sealable chamber for holding either a single substrate or a wafer cassette inserted at atmosphere therein.  
         [0016]      FIG. 4  is an orthographic view of an implemented embodiment combinable with the preceding embodiments. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     According to one embodiment of the invention, a linear substrate transfer system  10 , illustrated functionally in  FIG. 1 , transfers substrates  12 , such as wafers or rectangular reticles, between a substrate source on an input side on the right, such as a cassette  14 , and a processing side on the left, such as a single-wafer vacuum processing chamber  16 . The processing chamber  16  includes a pedestal  18 , which receives the substrate  12  and supports it during processing in harsh environments such as plasmas or high-temperature processing. A rotatable carousel  20  contained within a vacuum-tight transfer chamber  22  is capable of holding at least two substrates  12  at different angular positions of the carousel  20 . An actuator  24  supports the carousel  20  on a shaft  26  extending along a central axis of the carousel  20  and can both rotate the carousel  20  and raise and lower it. Thereby, the substrates  12  are moved between the input and output sides. The actuator  24  is preferably positioned below the transfer chamber  22  and the shaft  26  passes through the upper wall of the transfer chamber  22  in a rotatable and axially translatable seal. However, the actuator  24  and its shaft  26  my be positioned above the carousel  20 .  
         [0018]     The processing reactor  16  is vacuum isolated from the transfer chamber  22  by a selectively openable slit valve  03  through which the substrates  12  and associated transfer arms can pass. A first vacuum pumping system  32  holds the processing chamber  16  at a controlled, typically reduced pressure. Depending upon the type of processing performed in the processing chamber  16 , unillustrated gas sources may supply processing or inert gases into the processing chamber  16 . A second pumping system  34  controls the pressure within the transfer chamber  22  independently of the first pumping system  32  although the two pumping systems  32 ,  34  may include a single set of pump and independently controlled valves.  
         [0019]     The cassette  14  may be inserted into the transfer chamber  22  through a door  36  sealable to the upper or sidewall of the transfer chamber  22  and then placed on an elevator platform  40  while the transfer chamber  22  is opened to ambient pressure. Thereafter, the door  36  is closed and the second vacuum pumping system  34  reduces the pressure in the transfer chamber  22  to near the pressure within the processing chamber  16 . The cassette includes multiple shelves  42  for holding multiple substrates  12 , one above the other in parallel horizontal orientations. An elevator actuator  44  selectively raises and lowers an elevator shaft  46  passing through a seal in bottom wall of the transfer chamber  22  and supporting the elevator platform  40  and the supported cassette  14  supported thereon.  
         [0020]     A source linear transfer mechanism  50  transfers a substrate  12  between the input side adjacent the cassette  14  and the carousel  20 . In one set of embodiments of the invention, to be described in more detail later, the source linear transfer mechanism  50  is typically constrained to operation in a single horizontal plane. The elevator actuator  44  raises and lowers the cassette  14  to present a particular shelf  42  to the source transfer mechanism  50 , which inserts its empty blade below the selected shelf  42 . The elevator actuator  44  then lowers the cassette  14  to transfer the substrate  12  from the selected shelf  42  to the source transfer mechanism  50 . In transferring a processed substrate  12  back to the cassette  14 , the loaded blade is positioned above a selected empty shelf  42  and the cassette  14  is raised to transfer the substrate  12  from the blade to the shelf  42 .  
         [0021]     The process linear transfer mechanism  52 , predominantly disposed within the transfer chamber  22 , can transfer a substrate  12  between the carousel  12  and the pedestal  18  within the processing chamber  16  through the closable slit valve  30 . If the two linear transfer mechanisms  50 ,  52  are constrained to operated within a plane, vertical movement of the carousel  12  effects the transfer of the substrate  12  between the carousel  20  and the respective transfer mechanism  52 . In this case, either the pedestal  18  is vertically movable or vertically movable lift pins are included within it to effect substrate transfer between the pedestal  18  and the transfer mechanism  48 . The structure of the schematically linear transfer mechanisms  50 ,  52  will be described later in more detail.  
         [0022]     In operation, the source linear transfer mechanism  50  transfer a fresh substrate  12  from the cassette  14  to the position of a vacant sector or seat of the carousel  20  adjacent the cassette  14 . The carousel  20  vertically lifts the fresh substrate  12  off the source transfer mechanism  50  and then rotates, preferably in the raised position, to present the fresh substrate  12  to the process linear transfer mechanism  52 , and the carousel  20  lowers the substrate  12  to the process linear trans mechanism  52  which then transfers the fresh substrate  12  through the opened slit valve  30  onto the pedestal  18  within the processing reactor  16 . The process linear transfer mechanism  52  retracts from the processing chamber  16 , the slit valve  30  is closed, and processing commences. Meanwhile, the elevator actuator  44  raises or lowers the cassette  14  so that the source linear transfer mechanism  50  can transfer a fresh second substrate  12  from the cassette  14  onto the carousel  20  while the first substrate  12  is being processed.  
         [0023]     When substrate processing within the processing chamber  16  is completed, the slit valve  30  is opened, and the process linear transfer mechanism  52  transfers the processed first substrate  12  from the processing reactor  16  to the position of a vacant seat on the carousel  20 . The carousel  20  lifts the processed first substrate  12  from the process transfer mechanism  52  and is again rotated so that the fresh second substrate  12  is presented to the process transfer mechanism  52  for transfer into the processing chamber  16  and concurrently the processed second substrate  12  is presented to the source transfer mechanism  26 . The fresh second substrate is transferred into the processing chamber  16  by operation of the process transfer mechanism  52  and vertical movement of the carousel  20 , the slit valve  30  is closed, and processing commences for the second substrate  12  while the source transfer mechanism  50  transfers the first substrate  12  back into the cassette  14 . The elevator actuator  44  is again indexed so that the source transfer mechanism  22  can transfer a fresh third substrate  12  from the cassette  14  to the carousel  20 , which then lifts the substrate  12  onto the carousel  20 . Thereby, two transfer paths are created between the cassette  14  and the processing reactor  16 , and a fresh substrate  12  can pass a processed substrate  12  while both are supported on the carousel  20 . If the processed substrate  12  requires a substantial cool down period before being reloaded into the cassette  14 , the processed substrate  12  may wait on the carousel  20  or on the source transfer mechanism  40  while the next substrate  12  wafer is being processed in the reactor  16 .  
         [0024]     When all the substrates  12  contained in a cassette  14  have been processed and stored back in the cassette  14 , the door  36  of the transfer chamber  26  is opened while the slit valve  30  is closed and the second vacuum pump system  34  is isolated from the transfer chamber  26 . The first cassette  14  of processed substrates  12  is replaced on the elevator platform  40  by a second cassette  14  of fresh substrates  12 . The door  36  is closed and the second vacuum pump system  34  pumps the transfer chamber  26  down to approximately the processing pressure. The previously described substrate transfer and processing sequence is then repeated.  
         [0025]     In a second embodiment of a linear substrate transfer system  60 , schematically illustrated in the cross-sectional view of  FIG. 2 , substrates  12  are transferred one at a time in and out of the transfer chamber  26  through a source slit valve  62 . A robot operating at atmospheric pressure or a human operator may place a fresh substrate  12  on a ledge  64  outside of the source slit valve  62 . In operation, once a fresh substrate  12  is placed on the pedestal  18  in the process chamber  16  and the process slit valve  30  is closed to allow processing of the substrate, the transfer pump  34  is blocked and the source slit valve  62  is opened so that the transfer chamber  26  is vented to atmosphere. The source transfer mechanism  50  transfers the processed substrate  12  from the carousel  20  through the opened source slit valve  62  onto the ledge  64 , where either the operator or external robot replaces it with a fresh substrate  12 . The source transfer mechanism  50  transfers the fresh substrate  12  back through the source slit valve  62  onto the carousel  20 . The source slit valve  62  is closed, and the transfer vacuum pump  34  pumps the transfer chamber  26  to a reduced pressure. If desired, an inert gas such as nitrogen or argon is back filled into the transfer chamber  26 . The source substrate transfer and in particular the long pump down may occur while a substrate continues to be processed in the reactor chamber  16 .  
         [0026]     Once the processing is completed, the process slit valve  30  is opened but the processing chamber  16  is not exposed to the atmosphere previously held in the transfer chamber  26 . As described previously, the source transfer mechanism  50  exchanges the processed substrate  12  with a fresh substrate  12  on the carousel  20 . The source slit valve  30  is closed, the carousel  20  rotates, and the source transfer mechanism  50  exchanges the processed substrate  12  on the carousel  20  with a fresh substrate  12  from ledge  64 .  
         [0027]     In a variant embodiment, which combines the embodiments of  FIGS. 1 and 2 , the source slit valve  62  is replaced by a door in the transfer chamber wall, possibly the upper wall of  FIG. 1 , so that the substrate  12  is loaded or unloaded manually or with external equipment directly into or from the opened transfer chamber  26 . The substrate  12  may be loaded directly onto the source transfer mechanism  50  or onto an intermediate station.  
         [0028]     In a third embodiment of a linear substrate transfer system  70 , illustrated in  FIG. 3 , the ledge  64  forms part of a vacuum pumped single-substrate load lock chamber in conjunction with the second slit valve  62  between it and the transfer chamber  26  and a door  72 , which when closed seals to the ledge  64  to form the load lock chamber. Substrates  12  are transferred into and out of the system  70  by placing them or removing them from the ledge  64 . A third vacuum pump system  74  pumps the load lock chamber to near the pressure of the transfer chamber  26 . Thereafter, the second slit valve  62  is opened and the source transfer mechanism  50  transfers substrates  12  between the ledge  64  and the carousel  20 . Thereby, the transfer chamber  26  is never exposed to atmosphere. A variant of this embodiment places the cassette  14  and the elevator platform  50  within the just described load lock chamber so that the elevator actuator  44  can present different shelves  42  of the cassette  14  to the source transfer mechanism  50 .  
         [0029]     The system  70  can be modified to include an cassette elevator  40 ,  44 ,  46  of  FIG. 1  within the load-lock chamber formed by the door  72  and vacuum pump  74 . Once the cassette  14  is loaded into the load-lock chamber, it is pumped down while all its substrates are being processed.  
         [0030]     In both embodiments, the transfer chamber  22  remains pumped down for processing of a nearly unlimited number of substrates.  
         [0031]     The preceding embodiments are functionally presented. An implemented embodiment of the invention illustrated in the orthographic view of  FIG. 4  offers several advantages. A transfer system  80  includes a transfer chamber body  82 , which is vacuum sealed on its upper side by a top plate  84  and is sealed to the outside on its lower side by a base plate  86  having a shaft hole  88  and two parallel, laterally offset, and linearly extending slots  90 ,  92  formed through it between the two slots  90 ,  92 . A process port  96  is formed on one side lateral wall  94  to be sealed to the processing chamber  16  through the process slit valve  30 . A corresponding source port  97  penetrates the opposing side wall  98 , the form of which depends upon the vacuum isolation to the wafer source. The source port  97  may be a simple passage to a cassette accommodated within an adjacent part of the vacuum chamber, as in  FIG. 1 , or include a slit valve, as in  FIGS. 2 and 3 . The two slots  90 ,  92  may be horizontally offset to accommodate horizontally offset transfer mechanisms, and the process port  96  and the source port  97  are aligned with the two slots  90 ,  92  respectively.  
         [0032]     A two-seat carousel  100  is disposed within the transfer chamber body  82  and includes a horizontally extending carousel plate  102  and two horizontally opposed spiders  104 ,  106  laterally offset from each other along a horizontal axis, dependent from the carousel plate  102 , and designed to support rectangular reticles. Their shape would differ for circular wafers or other substrates. The spiders  104 ,  106  include respective pairs of dependent arms  108 ,  110  to support the reticles. The spiders  104 ,  106  may be modified for circular substrates. A spider shaft  114  supports the carousel plate  102  and is captured and vertically and rotationally moved by an actuator  116  having an actuator plate  118  sealed to the bottom, ambient side of the base plate  86 . The actuator  116  includes a pneumatic cylinder  120  and a motor  122 . The pneumatic cylinder  120  raises and lowers the spider shaft  114  while the motor  120  rotates it through a rotary section  124  including a ferro-fluidic rotary seal. A bellows  126  provides a vacuum seal for the vertical movement.  
         [0033]     A source transfer mechanism  130  and a process transfer mechanism  132  are disposed generally below the base plate  86  of the transfer chamber  82  and vacuum sealed on their upper sides to the lower surface of the base plate  86 . The details of the transfer mechanisms  130 ,  132  are disclosed in previously cited U.S. Pat. No. 6,935,828. They have respective risers  134 ,  136  rising through the two slots  90 ,  92  of the bottom plate  86  to support two arms  138 ,  140  having proximal ends fixed to the risers  134 ,  136  above the base plate  86 . Effectors or blades  142 ,  144  are fixed to distal ends of the arms  138 ,  140 . The illustrated blades  142 ,  144  are configured to support rectangular glass reticles. Other configurations are well known for semiconductor wafers and other substrates. The blades  142 ,  144  are sized to pass between the respective pairs of arms  106 ,  108  as the carousel  100  is raised and lowered to transfer reticles between the seats of the carousel  100  and the blades  142 ,  144   
         [0034]     Semi-tubular vacuum-tight nacelle covers  146 ,  148  seal the bottoms of the transfer mechanisms  130 ,  132 . Lead screws  152 ,  154  are turned by respective motors  154 ,  156  to linearly drive magnet assemblies, all in atmosphere. The magnet assemblies are magnetically coupled across the nacelle covers  146 ,  148  to linearly move the blades  142 ,  144  within the transfer chamber  82  and through its process and source ports  96 ,  97 .  
         [0035]     As illustrated, the arm  138  and its blade  142  of the source transfer mechanism  130  point in one direction to allow the blade  142  to move through the source port  97  between the interior of the transfer chamber body  82  and the substrate source, such as a wafer cassette. On the other hand, the arm  140  and blade  144  of the process transfer mechanism  132  point in the other direction to allow the blade  144  to move through the process port  96  between the interior of the transfer chamber body  82  and the process chamber. This configuration differs conventional wafer paddles in that the arm holding the blade is beneath the seat on which the substrate is placed and the paddle is backed onto the seat for substrate transfer. In contrast, conventional carousels use paddles having blades extending from arms towards the carousel.  
         [0036]     The size of the transfer chamber  82  may be reduced by making the clearance between the spider arms  108 ,  110  and the chamber walls only large enough to accommodate the risers  134 ,  136  of the transfer mechanisms  130 ,  132  in the extended position illustrated for the process transfer mechanism  132 . Then, in those conditions when the spider arms  108 ,  110  need to be lowered below the level of the spider arms  108 ,  110  while one of the spider arms  108 ,  110  contains a substrate that is not desired to be yet transferred, the associated transfer mechanism  130 ,  132  is projected out of the transfer chamber  82  leaving only the riser within the transfer chamber  82 . This situation occurs when a hot processed substrate has been loaded onto the carousel, the processed substrate is rotated to the source side and the fresh substrate is presented to the process side but needs to be lowered onto the process transfer mechanism without the hot substrate being transferred to the source transfer mechanism  130 . In this case, the source transfer mechanism  130  is projected out of the transfer chamber  82 . This limitation also allows the carousel rotation to be done in the down position if both transfer mechanisms  130 ,  132  are projected out of the transfer chamber  82  during rotation. As a result, all carousel rotation occurs between processing cycles while the processing chamber is open for the process transfer mechanism  132 . An unused shelf position of the cassette  14  may be used for temporary storage of the source transfer mechanism  130 .  
         [0037]     The transfer system  80  offers several advantages. Two stock transfer mechanisms may be used although different paddles and arms may be used depending on the application. The mechanisms and seals are all located below or at least even with the substrate flow. As a result, any particles generated within the system are unlikely to fall upon the substrates. The footprint of the system is small. This beneficial effect is enabled by the parallel offset transfer mechanism positioned below the carousel and having a throw nearly the size of the transfer chamber.  
         [0038]     The illustrated transfer system  80  applies easily to the systems  60  and  70  of  FIGS. 2 and 3 . Applying it to the system  10  of  FIG. 1  in which a cassette is contained within the transfer chamber  82  requires some redesign and a larger chamber. Alternatively, the cassette could be placed within a separate chamber open to the transfer chamber system  80  through the unillustrated and unvalved source port.  
         [0039]     The system  80  of  FIG. 4  can be adapted to place carousel actuator  24  or the linear transfer mechanisms  130 ,  132  above the carousel but the lower locations are preferred, especially for the transfer mechanisms.  
         [0040]     The carousel  106  of  FIG. 4  contains only two seats but the system  80  is simple and compact. The carousel may be designed to have more than two seats but the system will be considerably larger.  
         [0041]     It is possible to apply these transfer systems to more complex platforms than the single process chamber and single substrate source of the various described embodiments.