Abstract:
A functional load lock apparatus having two or more load lock chambers mounted on a central chamber which can be mounted on a single opening in a vacuum chamber such as a substrate processing platform for making integrated circuits on silicon wafers. Each load lock chamber preferably has a semi-cylindrical valve which remains sealed when the load lock chamber is open to atmospheric pressure. A wafer cassette holder positioned within each load lock chamber can be loaded and unloaded while the semi-cylindcical valves seal the vacuum chamber from atmospheric pressure. The semi-cylindrical valve pivots to an open position when the load lock chamber is under vacuum and the entire wafer cassette moves from the load lock chamber to the central chamber.

Description:
This is a continuation of application Ser. No. 08/746,859 filed on Nov. 18, 1996, now U.S. Pat. No. 5,961,269, issued Oct. 5, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to loading and unloading of vacuum chambers while a vacuum is maintained in the chamber. More specifically, the invention relates to a load lock apparatus for loading silicon substrates in a substrate processing platform. 
     2. Background of the Related Art 
     Cluster tools which combine numerous substrate processing units in a processing platform have become generally accepted as an effective and efficient concept in advanced microelectronics manufacturing. A cluster tool generally refers to a modular, multi-chamber, integrated processing system. It typically consists of a central wafer handling vacuum chamber and a number of peripheral vacuum process chambers. The silicon wafers go through a set of process steps under vacuum in the various process stations without being exposed to ambient conditions. The transfer of the wafers for the processes is managed by the wafer handling vacuum chamber which is also maintained under vacuum conditions. Cluster tools offer significantly higher yields on account of lower defect densities. Different types of cluster tools, such as linear or radial, with different types of architecture are possible. 
     Substrate processing platforms typically include at least two load lock chambers mounted on separate openings in the central wafer handling vacuum chamber for loading or unloading silicon wafers while the vacuum chamber remains under vacuum. The load lock chambers occupy valuable positions on the processing platform which would otherwise be used for additional process chambers. However, two chambers are usually required to maintain continuous operation such that wafers are processed from one load lock chamber while finished wafers are unloaded from the other chamber and new wafers are loaded. 
     FIG. 1 (prior art) shows a commercially available substrate processing platform offered by Applied Materials, Inc. under the trademark Endura®. The platform combines vacuum chambers designed to process silicon wafers at low/high pressure vacuum in the range of 10 −3  to 10 −8  torr. 
     Referring to FIG. 1, silicon wafers in a cassette  10  are introduced and withdrawn from the platform  52  through a first slit valve by a first load lock chamber  12  or through a second slit valve by a second load lock chamber  14 . A fist robot  16  having a blade  18  is located in a buffer chamber  20  to move a wafer  22  between various chambers  24 ,  26 ,  28  surrounding the buffer chamber  20 . A second robot  30  is located in a transfer chamber  32  to transfer a wafer  34  between various chambers  28 ,  36  surrounding the transfer chamber  32 . The buffer chamber  20  and the transfer chamber  32  are connected through two common chambers  28 . It is understood in the art that a wafer may be processed or cooled in one or more chambers for any number of times in any order to accomplish fabrication of a desired semiconductor structure on the wafer. A microprocessor controller  38  and associated software is provided to control processing and movement of wafers. 
     Attempts to connect two or more load lock chambers to a single slit valve in a processing platform have been unsuccessful. Such an apparatus must have internal valves large enough for the transfer of entire cassettes of wafers. Large valves are difficult to seal when the load lock chamber is open to the atmosphere and is mounted on a chamber that is under high vacuum. 
     It is an objective of the present invention to provide a load lock apparatus for mounting two load lock chambers on a single slit valve in a substrate processing platform. It is a further objective of this invention to provide a large valve in a load lock chamber which will remain sealed when the load lock chamber is mounted on an opening in a vacuum chamber under high vacuum conditions. 
     SUMMARY OF THE INVENTION 
     The present invention provides a functional load lock apparatus having two or more load lock chambers mounted on a central chamber which can be mounted on a single opening in a vacuum chamber such as a substrate processing platform for making integrated circuits on silicon wafers. 
     The present invention also provides a load lock apparatus having a semi-cylindrical valve mounted in a load lock chamber. The semi-cylindrical valve remains sealed when the load lock chamber is open to atmospheric pressure. A wafer cassette holder positioned within each load lock chamber can be loaded and unloaded while the semi-cylindrical valves seal the vacuum chambers from atmospheric pressure. The semi-cylindrical valve pivots to an open position when the load lock chamber is under vacuum and the entire wafer cassette moves from the load lock chamber to the central chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the above recited features, advantages and objects of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. 
     The appended drawings illustrate typical embodiments of this invention and are not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
     FIG. 1 (prior art) is a top schematic view of a radial cluster tool for batch processing of silicon wafers. 
     FIG. 2 is a front schematic view of a load lock apparatus of the present invention comprising two load lock chambers for mounting to a slit valve in a substrate processing platform such as the radial cluster tool of FIG. 1; 
     FIG. 3 is a side schematic view of the load lock apparatus of FIG.  2 . 
     FIG. 4 is a side sectional view of the load lock apparatus of FIG. 2 showing internal semi-cylindrical valves; 
     FIG. 5 is a rear sectional view of the load lock apparatus of FIG. 2 showing the internal semi-cylindrical valve and wafer cassettes; 
     FIGS. 6-9 are top sectional views of the load lock apparatus of FIG. 2; 
     FIGS. 10-12 are sectional views of a load lock chamber of the load lock apparatus of FIG.  2  showing movement of the semi-cylindrical valve; 
     FIGS. 13-15 are detail views of the semi-cylindrical valves including separate valve seals; and 
     FIG. 16 is a top schematic view of the load lock apparatus of FIG. 2 replacing both of the load lock chambers on the cluster tool of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention generally provides a load lock chamber having a two or more isolatable regions selectively communicable with a central transfer region. The load lock chamber is preferably mounted on a vacuum system so that the central transfer region is selectively communicable with the vacuum system. Each load lock region defines a loading port disposed in a sidewall and includes a door valve mounted in the loading port and a transfer port selectively communicable with the transfer region. A valve is rotatably disposed in each region to selectively communicate each load lock region with the transfer region. The central housing of the loadlock chamber preferably includes a transfer port which is selectively communicable with the vacuum system and a port selectively communicable with each load lock region so that wafers can be moved from each load lock region into the transfer region and then into the vacuum system. 
     In one embodiment of the present invention, a sealing valve is disposed in each load lock region to selectively communicate the load lock region and the transfer region. Preferably, the valve is a semi-cylindrical valve rotatably disposed in the load lock region. A wafer cassette holder is mounted on a shaft which is movably disposed in each load lock region to move the wafer cassette into the transfer region. An elevator mechanism, such as a stepper motor, moves the cassette holder within the load lock region to transfer the wafer cassette holder between the load lock region and the central transfer region. In one embodiment, at least two load lock housings are mounted on a central housing to eliminate the need for a second load lock chamber mounted on a separate opening in the vacuum chamber. 
     The load lock chamber of the present invention is preferably operated by a microprocessor controller provided with the vacuum system. The sequence and timing of operating the load lock chamber is provided so that a first load lock region is loaded and pumped down to a selected pressure so that a wafer cassette can be moved into the transfer region and wafers moved into the vacuum system. While the wafers are being processed, the second load lock region is loaded and pumped down to the desired pressure. After the wafers moved from the first region are processed, the wafer cassette is moved back into the load lock region and the valve disposed between the transfer region and the load lock region is closed. The wafer cassette in the second load lock region is then moved into the transfer region and the wafers loaded into the system. 
     A preferred load lock apparatus for mounting on a vacuum system having two or more load lock chambers which have semi-cylindrical valves disposed in the ports located between the load lock chambers and are the central transfer chamber will be described in references to FIGS. 2-15. The various chamber components are preferably machined from aluminum, but may be comprised of any other material known in the art and compatible with vacuum processing. 
     FIG. 2 is a front view of a preferred load lock apparatus of the present invention comprising two load lock chambers for mounting to a slit valve in a substrate processing platform such as the radial cluster tool of FIG.  1 . The load lock chambers are preferably vertically aligned around a central chamber to make room for processing chambers on adjacent slit valves. Referring to FIG. 2, the load lock apparatus  40  comprises a central housing  42  having a slit  48  for mounting adjacent a slit valve on a processing platform The slit  48  will usually have a width corresponding to passage of a silicon wafer. However, the use of double wide slits for passage of two wafers side-by-side is also contemplated. Each substrate cassette holder  60 ,  104  (shown in FIG. 5) may support two substrates in a side-by-side relationship. The central housing  42  has a vacuum port  54  for connection to a vacuum system commonly provided with the processing platform  52  or optionally provided with the load lock apparatus. 
     The load lock apparatus further comprises a first load lock housing  56  mounted on the central housing  42 . A door valve  66  having external knobs  68  which engage the first load lock housing  56  provide access for loading and unloading wafers as described for FIG. 5 below. Preferably, the door valve  66  is operated automatically by the processing platform. Automatic door valves are used commercially on the load lock chambers of FIG.  1  and can be included on the present invention. A vacuum port  70  on the first load lock housing  56  connects to a vacuum system commonly provided with the processing platform  52  or optionally provided with the load lock apparatus. The vacuum system typically can achieve pressures lower than 0.01 Torr in a load lock chamber. 
     Rotatable seals  76  are mounted in both sides of the load lock housing  56  and pivot pins  82  are rotatably mounted in the rotatable seals  76 . Pneumatic actuating arms  78  are externally fastened at one end to the load lock housing  56  and the other ends are pivotally linked to pivot arms  80  which are fastened to the pivot pins  82 . External components of a first cassette elevator  90  are protected by a shield  98  which is mounted on the load lock housing  56  and also secures an end of the pneumatic actuating arms  78 . Expansion or contraction of the pneumatic actuating arms  78  rotates the pivot pins  82  and operates internal components as described for FIG. 4 below. 
     The first cassette elevator  90  moves a cassette of wafers within the apparatus as described for FIG.  5  and externally includes a shaft  92  which slides through a packing gland  94  mounted on the load lock housing  56 . 
     The load lock apparatus  40  further comprises a second load lock housing  100  mounted on the central housing  42 . A door valve  110  having knobs  112  which engage the second load lock housing  100  provide access for loading and unloading wafers as described for FIG. 5 below. Preferably, the door valve  110  is operated automatically by the processing platform  52  as described above. A vacuum port  114  on the second load lock housing  100  connects to a vacuum system as described for the vacuum port  70  on the first load lock housing  56 . 
     The load lock apparatus further comprises rotatable seals  120  and pivot pins  126  on the second load lock housing  100  as described for the first load lock housing  56 . Pneumatic actuating arms  122  are fastened to the load lock housing  100  at one end and the other ends are linked to pivot arms  124  which are fastened to the pivot pins  126 . External components of a second cassette elevator  130  are protected by a shield  138  which is mounted on the load lock housing  100  and also secures an end of the pneumatic actuating arms  122 . Expansion or contraction of the pneumatic actuating arms  122  rotates the pivot pins  126  and operates internal components described for FIG. 4 below. 
     The second cassette elevator  130  moves a second cassette of wafers within the apparatus as described for FIG.  5  and externally includes a shaft  132  which slides through a packing gland  134  mounted on the second load lock housing  100 . 
     FIG. 3 is a side view of the load lock apparatus of FIG.  2  and shows the first pneumatic arms  78  in an extended position for comparison to a retracted position shown for the second pneumatic arms  122 . 
     FIG. 4 is a side sectional view of the load lock apparatus of FIG. 2 showing internal chambers and semi-cylindrical valves. The central housing  42  internally comprising first  44  and second  46  openings and the slit  48  for transferring substrates between a central chamber  50  within is the central housing and the processing platform  52 . The first load lock housing  56  internally comprising a first opening  58  adjacent the first opening  44  of the central housing  42  for transferring a first substrate cassette holder  60  (FIG. 5) between the central chamber  50  and a first load lock chamber  62  within the first load lock housing  56 . The first load lock housing  56  further comprises a second opening  64  for loading or unloading the first substrate cassette holder  60  through the door valve  66 . 
     The load lock apparatus  40  internally comprises a first semi-cylindrical valve  72  pivotally mounted to the first load lock housing  56 . The semi-cylindrical valve  72  is fastened by screws or the like at each side to flexible brackets  74  which are fastened to eccentric supports  75 . Each eccentric support  75  is fastened to one of the pivot pins  82  which pass through the load lock housing  56  as described for FIG.  2 . Expansion or contraction of the pneumatic actuating arms  78  rotates the eccentric supports  75  and moves the semi-cylindrical valve  72  between an open position and a closed position to selectively communicate the first load lock chamber  62  and the central chamber  50 . Connection of the semi-cylindrical valve  72  to the load lock housing  56  can be achieved in a variety of ways. The flexible brackets  74 , eccentric supports  75 , and rotatable seals  76  shown in FIG. 4 minimize vacuum leaks while m m g wear of internal valve components in the load lock chamber  62 . 
     The second load lock housing  100  internally comprises a first opening  102  adjacent the second opening  46  of the central housing  42  for transferring a second substrate cassette holder (FIG. 5) between the central chamber  50  and a second load lock chamber  106  within the second load lock housing  100 . The second load lock housing  100  further comprises a second opening  108  for loading or unloading the second substrate cassette holder  104  through the door valve  110 . 
     The load lock apparatus further comprises a second semi-cylindrical valve  116  pivotally mounted to the second load lock housing  100  by flexible brackets  118 , eccentric supports  119 , pivot pins  126 , and rotatable seals  120  as described for the first semi-cylindrical valve  72 . The semi-cylindrical valve  116  has the same valve stops  83  and the same movement (FIGS. 10-12) described for the first semi-cylindrical valve  72 . 
     FIG. 5 is a rear sectional view of the load lock apparatus of FIG. 2 showing the internal semi-cylindrical valves and wafer cassettes. The first semi-cylindrical valve  72  is removed from the drawing to show a semi-cylindrical surface  88  on the first load lock housing  56  for seating the first semi-cylindrical valve. The load lock apparatus  40  further comprises the first cassette elevator  90  mounted to the first substrate cassette holder  60  for moving the first substrate cassette holder between the first load lock chamber  62  and the central chamber  50 . The first cassette elevator  90  can be any means for moving the cassette holder  60  such as the shaft  92  which slides through the packing gland  94  mounted on the load lock housing  56 . Preferably, the shaft  92  engages a screw drive system  96 FIG. 3) which aligns the cassette holder  60  with the slit  48  in the central chamber  50 . 
     The load lock apparatus  40  further comprises the second cassette elevator  130  mounted to the second substrate cassette holder  104  for moving the second substrate cassette holder between the second load lock chamber  106  and the central chamber  50 . The second cassette elevator  130  can be any means for moving the cassette holder  104  such as the shaft  132  which slides through the packing gland  134  mounted on the load lock housing  100 . Preferably, the shaft  132  engages a screw drive system  136  (FIG.  3 ). 
     Each substrate cassette holder  60 ,  104  may have individual slits for receiving wafers or optionally may house an external wafer cassette which slips into the substrate cassette holder to accelerate loading and unloading. Each cassette elevator  90 ,  130  is vertically indexable so that every substrate in each substrate cassette holder  60 ,  104  can be delivered by the first robot  140  through the slit  48  in the central housing  42 . For example, computer-controlled, stepper motor-driven lead screw drive systems  96 ,  136  may be used to position the substrate cassette holders  60 ,  104  for loading and unloading wafers through the door valves  66 ,  112  in each load lock housing  42 ,  100  and for loading and unloading wafers through the slit  48  in the central housing  42 . The screw drive systems are currently used to perform the same function on the commercially available platform of FIG.  1 . 
     FIGS. 6-9 show horizontal cross-sections through chambers inside the load lock apparatus as indicated in FIG.  5 . FIG. 6 shows a cross-section through the first load lock chamber  62  looking toward the semi-cylindrical surface  88  on the first load lock housing  56 . The view also shows the first opening  58  in the first load lock housing  56  and the valve stops  83 . FIG. 7 show a cross-section through the central chamber  50  looking toward the first opening  102  in the second load lock housing  42 . FIG. 8 is a cross-section through the second load lock chamber  106  and the shaft  132  which mounts the second substrate holder  104 . FIG. 9 is a cross-section through the shaft  132  looking toward the packing gland  134  outside the second load lock housing  100 . 
     FIGS. 10-12 show the movement ofthe first semi-cylindrical valve  72 . Rotation of the pivot pins  82  also rotates the eccentric supports  75  which mount the flexible brackets  74  and the semi-cylindrical valve  72 . Initial rotation of the pivot pins  42  moves the semi-cylindrical valve  72  from an open position, FIG. 10, to a closed position, FIG. 11, wherein the flexible brackets  74  are blocked by the valve stops  83 . Further rotation of the pivot pins  82  causes the flexible brackets  74  to flex away from the eccentric supports  75  and push the semi-cylindrical valve  72  outward to contact the semi-cylindrical surface  88  on the load lock housing  56 . Venting of the load lock chamber  62  to atmospheric pressure pushes the semi-cylindrical valve  72  tighter toward the semi-cylindrical surface  88 . Thus, the high pressure differential between the load lock chamber  62  and the central chamber  50  during wafer loading and unloading makes a tighter seal around the semi-cylindrical valve  72  and assists in sealing the central chamber  50 . The semi-cylindrical valve  72  is not moved while a pressure differential exists between the central chamber  50  and the load lock chamber  62 . The semi-cylindrical valve  72  is opened after the load lock chamber  62  is evacuated to about the same vacuum as the central chamber  50 . Retraction of the pneumatic arms  78  opens the semi-cylindrical valve  72  by pulling the semi-cylindrical valve  72  away from the semi-cylindrical surface  88  on the load lock housing  56 . 
     FIGS. 13-15 are detail views of the semi-cylindrical valves showing detachable valve seals which can be replaced when worm. FIG. 13 is a partial section view of the semi-cylindrical valve  72  showing the flexible brackets  74  supporting each end of the semi-cylindrical valve. The semi-cylindrical valve  72  preferably has a detachable seal  84  which is formed by machining channels in both sides of a flat aluminum sheet and rolling the sheet to the desired shape. Durable elastomer seals  86 , such as VITON fluoroelastomer (a trademark of du Pont), are adhered to the channels in the detachable seal  84 . The outer elastomer seal  86  rests against the semi-cylindrical surface  88  around the first opening  58  in the first load lock housing  56 . The inner elastomer seal  86  is preferably the same as the outer seal, but could be an  0 -ring which is not adhered to the channel in the detachable seal  84 . FIG. 14 is a cross-section through the detachable seal  84  and elastomer seals  86 . FIG. 15 is a plane view of the detachable seal  84  showing that the elastomer seal  86  is positioned near the perimeter of the detachable seal  84 . 
     FIG. 16 shows the load lock apparatus  40  of the present invention mounted on the commercially available substrate processing platform  52  of FIG. 1. A first robot  140  having a blade  142  is located in a buffer chamber  144  to move a wafer  146  between various chambers  150 ,  152 ,  154  surrounding the buffer chamber  144 . A second robot  160  is located in a transfer chamber  162  to transfer a wafer  164  between various chambers  154 ,  166  surrounding the transfer chamber  162 . The buffer chamber  144  and the transfer chamber  162  are connected through two cooling chambers  154 . It is understood in the art that a wafer may be processed or cooled in one or more chambers for any number of times in any order to accomplish fabrication of a desired semiconductor structure on the wafer. A microprocessor controller  180  and associated software controls movement and processing of wafers throughout the system. 
     Alternative means for connecting the semi-cylindrical valves  72 ,  116  to the first and second load lock housings  56 ,  100  include rigid brackets that are fastened to the semi-cylindrical valves and to the pivot pins  82 ,  126  without the eccentric supports  75 ,  119 . Pushing or pulling the semi-cylindrical valves with respect to the semi-cylindrical surfaces  88  on the load lock housings  56 ,  100  can be accomplished with a rigid bracket by eccentrically mounting the pivot pins  82 ,  126  in the rotatable seals  76 ,  120  and fastening external levers to the rotatable seals. When the cylinder valves are in a closed position, the external levers are separately actuated to rotate the seals and shift the pivot pins toward the semi-cylindrical surfaces  88 . As another alternative, the flexible brackets  74 ,  118  could be replaced by hinged brackets that are spring biased in a retracted position when the valves are open. Rotation of the hinged brackets will also be blocked by the valve stops  83  and continued rotation of the pivot pins  82 ,  126  will straighten the hinged bracket and push the semi-cylindrical valve against the semi-cylindrical surface  88 . 
     Operation of the load lock apparatus  40  is very similar to operation of two separate load lock chambers  12 ,  14  after the load lock apparatus  40  has been mounted on the substrate processing platform  52 . The central chamber  50  is preferably connected by vacuum port  54  to the vacuum source provided with the platform  72 . The vacuum port  54  is used to evacuate the central chamber  50  in the load lock apparatus  40 , but may be used to evacuate the entire buffer chamber  144  in the platform  72 . The central chamber  50  will typically be purged with dry nitrogen to remove moisture and evacuated to a pressure below 0.01 Torr while both semi-cylindrical valves  72 ,  116  are closed. The load lock chambers  62 ,  106  are also purged with dry nitrogen while the central chamber  50  is purged and evacuate&amp; The central chamber  50  is generally maintained at the same conditions as the buffer chamber  144  during all process steps. 
     After the central chamber  50  is evacuated, the semi-cylindrical valves  72 ,  116  tightly seal the central chamber  50  and purging of the first load lock chamber  62  can continue while wafers are loaded in the first substrate cassette holder  60 . The first door valve  66  is then closed and the first load lock chamber  62  is evacuated through vacuum port  70  to a pressure less than 0.01 Torr. The first semi-cylindrical valve  72  is then opened and the first cassette mover  90  moves the first substrate cassette holder  60  into the central chamber  50 . 
     While wafers in the first substrate cassette holder  60  are being processed in the platform  52 , the wafer loading procedure is repeated for the second substrate cassette holder  108  in the second load lock chamber  106 . After all wafers in the first substrate cassette holder  60  have been returned from the platform  52 , the first cassette holder  60  is returned to the first load lock chamber  62 , the first semi-cylindrical valve  72  is closed, and the first load lock chamber  62  may be vented and purged with a gas such as dry nitrogen. The second door valve  110  is then closed and the second load lock chamber  106  is evacuated through vacuum port  114  to a pressure below 0.01 Torr. Wafers in the second substrate cassette holder  104  are then moved into the central chamber  50  and processed in the platform  52  while processed wafers are removed from the first cassette holder  60 . 
     Operation of the platform  52  continues until all wafers in the second substrate cassette holder  104  are processed and returned to the cassette holder  104 . The second cassette holder  104  is returned to the second load lock chamber  106  and the second semi-cylindrical valve  116  is closed. The second load lock chamber  106  may then be vented and purged with a gas such as dry nitrogen prior to unloading the processed wafers and loading new wafers. 
     Loading and unloading of wafers through the door valves  66 ,  110  typically takes place in a controlled clean room using robots which minimize contamination of the wafers. The load lock  25  apparatus  40  is preferably controlled by the microprocessor controller  180  which controls the substrate processing platform  52  as well as other components in the clean room. The load lock apparatus  40  preferably has the same input/output devices used for the available load lock chambers  12 ,  14  and can thus replace the available chambers  12 ,  14  with little or no modification of the microprocessor controller  38  or associated software. Of course, an existing substrate processing platform can be modified or a new substrate processing platform can be designed, by persons skilled in the art, to include a load lock apparatus of the present invention using the preceding disclosure. 
     While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof The scope of the invention is determined by the claims which follow.