Abstract:
A wafer processing apparatus is provided with a wafer carrier comprising a doorplate, a pedestal including one or more legs to support the pedestal on the doorplate, and a wafer rack positionable on the pedestal. A pedestal lock is connected to the doorplate and is selectively engageable with at least one of the legs to lock the pedestal to the doorplate. A lock is further provided to selectively engage at least one of the wafer rack and the pedestal to lock the wafer rack to the pedestal. The pedestal is thereby prevented from falling off of the doorplate, and the wafer rack is prevented from falling off of the pedestal, during earthquake-induced vibrations and accelerations.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to semiconductor processing equipment and more particularly to earthquake protection for such equipment. 
     2. Description of the Related Art 
     Semiconductor workpieces, or wafers, are typically loaded into wafer racks or boats for processing in a batch reactor. If the reactor is a vertical reactor, the wafer rack is typically supported on a pedestal. In the system disclosed in PCT Publication No. WO 99/38199, published Jul. 29, 1999, the pedestal, in turn, is supported on a doorplate. The wafer rack and pedestal are lifted into the reactor from below. The doorplate serves to seal the internal chamber of the reactor from a surrounding processing chamber during processing of the wafers. 
     The wafer carrier and pedestal are typically made of quartz, and are relatively fragile. As such, they are susceptible to damage caused by earthquakes. During an earthquake, the wafer rack has a tendency to vibrate or rock back and forth on the pedestal. Similarly, the pedestal has a tendency to vibrate or rock back and forth on the doorplate. If the vibration or rocking caused by the earthquake is significant, the wafer rack can fall off of the pedestal, and the pedestal can fall off of the doorplate. As a result, damage to the wafer rack, pedestal, wafers, and the reactor or surrounding processing chamber can occur. The loss of an entire rack of large wafers (e.g., 100) can be quite expensive. 
     Accordingly, a need exists for semiconductor processing equipment that is equipped to prevent damage that can be caused by earthquakes. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, a wafer carrier is provided comprising a wafer rack adapted to receive a plurality of wafers and a pedestal supporting the wafer rack. A lock is provided that is engageable with at least one of the wafer rack and the pedestal to selectively lock the wafer rack to the pedestal. The wafer rack is thus prevented from falling off of the pedestal as a result of earthquake-induced vibrations and accelerations. 
     In accordance with another aspect of the present invention, a wafer processing apparatus is provided, comprising a doorplate, a pedestal including one or more legs to support the pedestal on the doorplate, and a wafer rack positionable on the pedestal. A pedestal lock is connected to the doorplate and is selectively engageable with at least one of the legs to lock the pedestal to the doorplate. The pedestal is thereby prevented from falling off of the doorplate as a result of earthquake-induced vibrations and accelerations. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an exemplary wafer processing system in accordance with the prior art. 
     FIG. 2 is a schematic plan view of the system of FIG.  1 . 
     FIG. 3 is an isometric view of the pedestal and the lower portion of the wafer rack for a system similar to that of FIG. 1, constructed in accordance with a preferred embodiment of the present invention. 
     FIG. 4 is an elevational view of the pedestal and lower portion of the wafer rack of FIG. 3 in an assembled position. 
     FIG. 5 is a top plan view of the pedestal and wafer rack of the system of FIG. 3, with a lock engaged with the beam of the pedestal. 
     FIG. 6 is a side elevational view of the pedestal, wafer rack and lock of FIG. 5, illustrating the operation of the lock. 
     FIG. 7 is an elevational view of the lower portion of the pedestal of FIG.  5  and an underlying doorplate. 
     FIG. 8 is a cross-sectional view taken through the legs of the pedestal along lines  8 — 8  in FIG.  7 . 
     FIG. 9 is a cross-sectional view taken through the pedestal lock, pedestal leg, screw and doorplate of the system of FIG. 1 along lines  9 — 9  in FIG.  8 . 
     FIG. 10 is a perspective view of the pedestal lock and door plate. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIGS. 1 and 2, an exemplary wafer processing apparatus is illustrated and indicated generally by the reference numeral  1 . The exemplary apparatus  1  of FIGS. 1 and 2 comprises a housing  2  and is generally installed in a so-called “clean room.” In addition to the housing  2 , partitions  3 ,  4  and  5  are also present. The housing  2  delimits, with the partition  3 , a processing area or chamber  21 . In this example, the processing area  21  comprises vertical furnaces  6 ,  7 . The housing  2  and the partitions  3  and  4  define a wafer handling chamber  22 . A cassette transfer chamber  23  is defined between the housing  2  and partitions  4  and  5 . An input/output station, to transfer cassettes into and out of the system  1 , is indicated by reference numeral  33 . 
     Wafers  13  are supplied in cassettes  10 , which are placed on the input/output station  33 . A cassette handling device  31  transfers the cassettes  10  from the input/output station  33  through a closable opening  34  into a cassette store  8  located in the cassette transfer chamber  23 . The cassette store  8  is provided with a number of vertically aligned rotary platforms  27  on which the cassettes  10  are stored. The cassette handling device  31  is movable in a vertical direction by means of an elevator  35  so that the different platforms  27  can be reached. The cassette handling device  31  is provided with a cassette end effector  32 , which has dimensions a little smaller than those of a series cut-outs  26  in the rotary platforms  27 . When the cassette handling device  31  has transferred a cassette into the store  8 , an end effector  32  of the device  31  can be lowered through one of the cut-outs  26  in one of the platforms  27  to place the cassette on the platform  27 . Subsequently, the cassette handler  31  can be retracted from the cassette store  8 . The cassette handling device  31  is mounted such that it is able to transfer cassettes between the input/output station  33  and the store  8 . The device  31  is also capable of transferring cassettes between the store  8  and a rotatable cassette transfer platform  30 , or between the input/output station  33  and the rotatable cassette transfer platform  30 . 
     The rotatable cassette transfer platform  30  is constructed such that, on rotation, the cassette is placed against the partition  4  between the cassette transfer chamber  23  and the wafer handling chamber  22 . The partition  4  is provided with a closure and a closure mechanism, together forming an interface schematically indicated by the reference numeral  37 . After placing the cassette against the interface  37  in the partition  4 , the closure mechanism grips and unlocks the closure of the cassette and simultaneously opens the closure in the partition  4  and the closure of the cassette. 
     A wafer handling device  24  within the wafer handling chamber  22  transfers wafers between the cassette concerned and a wafer carrier  12 . The wafer handling device  24  comprises a robot arm  28  with a wafer end effector  29 , numbered in FIG.  1 . As described below, each of the wafer carriers  12  preferably comprises a wafer boat or rack supported on a pedestal. A doorplate is preferably provided below each of the pedestals. 
     After completion of the loading of wafers into the wafer carrier  12 , a transfer arm  16  swings about pivot point  18  and moves the wafer carrier  12  upon a support surface  17  through an openable closure  19  in the partition  3  from the wafer handling chamber  22  into the processing chamber  21 . The processing chamber  21  is provided with a rotary transfer platform  11 , supporting the wafer carrier  12 . Two reactors, which in this case comprise furnaces  6 ,  7 , are arranged in the processing chamber  21 . The furnaces  6 ,  7  are positioned vertically and wafer carriers  12 , filled with wafers  13 , are introduced vertically into the furnaces  6 ,  7  from below. To this end, each furnace  6 ,  7  has an insertion arm  14 , which is movable in the vertical direction and sized to fit through slots  15  in the transfer platform. The doorplates below the wafer racks serve to seal the reactors from the outside processing chamber when the wafer carriers  12  are lifted up into the reactors. 
     The treatment of a large number of wafers can be carried out as follows: The operator, shown diagrammatically in FIG. 1, loads the store  8  by introducing a number of cassettes  10  on the input/output station  33  and carrying out control operations on a control panel  36 . Each of the cassettes  10  is transferred from the input/output station  33  with the aid of the cassette handling device  31  into the storage compartments  9  made for these cassettes in the store  8 , specifically on the stacked rotary platforms  27 . By rotation of the store  8  and use of the elevator  35 , it is possible to fill various compartments with the cassettes  10 . After filling the store  8 , no further human interaction is required with this exemplary automated installation. 
     The cassettes  10  concerned are then removed from the store  8  by the cassette handler device  31  and placed on the cassette transfer platform  30 . The cassette transfer platform  30  comprises two levels, schematically indicated in FIG. 1, each level capable of receiving a cassette, where the two levels can be rotated independently of one another. Upon rotation of the cassette transfer platform  30 , the cassettes are placed against the partition  4 . After opening of the closure of the cassette, together with the closure  37  in the partition  4 , the wafers are removed by the wafer handler  24  and placed in a wafer carrier  12 . After the wafer carrier  12  has been filled, and becomes available for one of the reactors  6 , 7 , the closure  19  in partition  3  is opened and the wafer boat  12  is placed on the transfer platform  11  by the transfer arm  16 . The transfer platform  11  then moves the wafer carrier  12  within the process chamber  21  to a position below the reactor to be loaded. Then the insertion mechanism or elevator  14  moves through the slot  15  in the transfer platform  11  to lift the carrier  12  into the reactor  6  or  7 . Treated wafers move counter to the course described above after being lowered an cooled within the chamber  21 . 
     With reference now to FIGS. 3 and 4, a preferred embodiment of the wafer carrier  12  that can be used in the exemplary wafer processing apparatus  1  is illustrated. As noted above, the wafer carrier  12  comprises a wafer boat or rack  38  and a pedestal  40 . In the illustrated embodiment, the pedestal  40  comprises a generally cylindrical main portion  48  and a generally cylindrical beam portion  50  that extends upwardly from a top surface of the main portion  48 . A number of legs  54  extend below the main portion  48  to support the pedestal  40 . In the illustrated embodiment, the pedestal  40  has four legs  54 , one of which is hidden behind the middle leg  54  in FIG.  4 . 
     The wafer rack  38  illustrated in FIGS. 3 and 4 comprises a generally disc-shaped base  58  and a number of columns  60  that extend upwardly from the base  58 . In the illustrated embodiment, the wafer rack  38  includes three columns  60  that are spaced around a perimeter of the base  58 . The columns  60  are provided with a number of slots  64  for supporting individual wafers in the wafer rack  38 . Preferably, greater than  40  such slots  64  are provided and  100  slots are provided in the illustrated embodiment. A number of legs  66  extend below the base  58  to support the wafer rack  38  on the pedestal  40 . 
     In the illustrated embodiment, an opening  70  is provided in the center of the base  58  of the wafer rack  38 . When the wafer rack  38  is placed on top of the pedestal  40 , the beam portion  50  of the pedestal  40  extends upwardly through the opening  70  in the base  58 . Preferably, the diameter of the opening  70  is only slightly larger than the diameter of the beam portion  50  to help prevent lateral rocking of the wafer rack  38  on the pedestal  40 . 
     As illustrated in FIGS. 3-5, a linear groove  74  is formed in a side of the beam portion  50  of the pedestal  40 . Preferably, the groove  74  is located a distance above the top surface of the main portion  48  such that, when the wafer rack  38  is situated on top of the pedestal  40 , the groove  74  is located just above a top surface of the base  58  of the wafer rack  38 , as best seen in the view of FIG.  4 . 
     The wafer carrier  12  desirably also comprises a lock  80  (FIG. 5) for locking the wafer rack  38  to the pedestal  40 . In the illustrated embodiment, the lock  80  comprises a generally linear segment  82  and a curved segment  84  that extends from one end of the linear segment  82  towards the other end. Preferably, the lock  80  extends greater than  180  degrees around the beam portion  50  of the pedestal  40 . 
     To engage the lock  80 , the linear segment  82  is placed in the groove  74  of the beam portion  50 . The lock  80  is initially oriented vertically so that the curved segment  84  extends above the linear segment  82 . The curved segment  84  is then rotated over the top of the beam portion  50 , as illustrated in FIG. 6, until the curved segment  84  rests against the top surface of the base  58 . The curved segment  84  extends partially around the beam portion  50  of the pedestal  40 , preferably greater than 180 degrees around, to prevent the linear segment  82  of the lock  80  from sliding out of the groove  74 . To disengage the lock  80 , the curved segment  84  is lifted off of the base  58  and rotated back over the top of the beam portion  50 . The linear segment  82  can then be removed from the groove  74 . 
     When engaged, the lock  80  prevents movement of the wafer rack  38  relative to the pedestal  40 . The linear portion  82  of the lock  80  is trapped in the groove  74  in the beam portion  50  of the pedestal  40 . When the wafer rack  38  is moved upwardly away from the pedestal  40 , the linear segment  82  of the lock  80  abuts the top surface of the base  58  of the wafer rack  38 , preventing further movement of the wafer rack  38  relative to the pedestal  40 . 
     Like the rest of the wafer carrier  12 , the lock  80  is preferably formed of a material that is process-compatible (i.e., non-contaminating) and capable of withstanding the high temperatures (e.g., greater than about 400° C.) to which the wafer carrier  12  is exposed during processing. Preferably, the lock is formed of quartz or silicon carbide (SiC). 
     With reference now to FIG. 7, a doorplate  42  and lower portion of the pedestal  40  are shown. The main portion  48  of the pedestal  40  is supported above the doorplate  42  by the pedestal legs  54 . 
     FIG. 8 is a cross-sectional view taken through the pedestal legs  54  along lines  8 — 8  in FIG.  7 . As illustrated in FIG. 8, a pedestal lock  90  is provided between the doorplate  42  and the main portion  48  of the pedestal  40 . In the illustrated embodiment, the pedestal lock  90  is generally Y-shaped and comprises a stem  96  and a pair of arms  98  that extend outwardly from the stem  96 . A slotted opening  102  is provided in the stem  96  and in each of the arms  98 . A screw  106  extends through each of the slotted openings  102  and into the doorplate  42  to slidably secure the pedestal lock  90  to the door plate  42 . 
     Referring still to FIG. 8, in the illustrated embodiment, a second opening  110  is provided in each of the lock arms  98  inwardly of the slotted openings  102 . Each of the second openings  110  comprises a circular portion  112  and a slotted portion  114  that extends from the circular portion  112 , preferably parallel to the slots  102 . The circular portions  112  of the openings  110  preferably have a diameter that is slightly larger than a diameter of the pedestal legs  54 . The slotted portions  114  of the openings  110  preferably have a more narrow lateral width that is slightly less than the diameter of the pedestal legs  54 . 
     FIG. 9 is a cross-sectional view taken through the pedestal lock  90 , pedestal leg  54 , screw  106  and doorplate  42  along lines  9 — 9  in FIG.  8 . As illustrated in FIG. 9, the doorplate  42  of the illustrated embodiment comprises a main plate  120  and a lip seal  126  extending upwardly and outwardly from the main plate  120  around a circumference of the main plate  120 . The main plate  120  desirably is provided with blind holes  130  that extend from the upper surface of main plate  120  in a direction perpendicular to the upper surface, the locations of which correspond to the locations of the legs  54  of the pedestal  40 . When the pedestal  40  is situated on top of the doorplate  42 , the pedestal legs  54  extend into the holes  130  in the main plate  120 . 
     Preferably, the screws  106  are provided with a lower threaded portion  107  and an upper portion  108  having a larger diameter than the threaded portion  107 . The main plate  120  is provided with threaded blind holes  132  extending from the upper surface of main plate  120  in a direction perpendicular to the upper surface and are designed to receive and mate with the lower threaded portion  107  of the screws  106 . The length of the upper portion  108  of the screws  106  is preferably slightly greater than the thickness of the pedestal lock  90 . A separate washer  109  is provided below the pedestal lock  90 . The screws  106  can be tightened against the door plate  42  to slidably secure the pedestal lock  90  to the doorplate  42  and allow the pedestal lock  90  to move a predetermined distance in the vertical direction between the washers  109  and the screw  106  heads. 
     Referring still to FIG. 9, the pedestal legs  54  desirably each have a notch  134  formed in a side thereof. To engage the pedestal lock  90 , the lock  90  is slid relative to the pedestal  40  and doorplate  42  so that the legs  54  of the pedestal  40  extend through the slotted portions  114  of the lock arm openings  110 , as illustrated in FIGS. 8-10. Since the lateral width of the slotted portions  114  of the openings  110  is less than the diameter of the legs  54 , the lock arms  98  extend into the notches  134  to trap the legs  54 , thereby locking the pedestal  40  to the doorplate  40 . 
     To disengage the pedestal lock  90 , the lock  90  is slid relative to the pedestal  40  and doorplate  42  so that the legs  54  of the pedestal  40  extend through the circular portions  112  of the lock arm openings  110 . Since the diameter of the circular portions  112  of the openings  110  is larger than the diameter of the pedestal legs  54 , the legs  54  are freed from the lock arms  98  and the pedestal  40  can thus be lifted off of the doorplate  42 . 
     FIG. 10 is a perspective view of the door plate  42  and the pedestal lock  90 . A tab  160  is punched in the pedestal lock  90  near an end of the slotted opening  102  in the stem  96 . The tab  160  is bent downwardly towards the doorplate  42 . A slot (not shown) is provided in the doorplate  42  below the tab  160  so that, when the pedestal lock  90  is in the locked position, the tab  160  extends into and is retained in the slot to prevent the pedestal lock  90  from sliding to the unlocked position. An upwardly extending tab  164  and an opening  166  preferably are provided at an end of the stem  96 . The upwardly extending tab  164  and opening  166  are intended to cooperate with a locking tool (not shown) to facilitate movement of the lock  90  between the locked and unlocked positions. 
     The wafer carrier  12  of the preferred embodiments can be manufactured with tooling similar to that used for manufacturing conventional wafer carriers, thereby minimizing retooling costs. The wafer carrier  12  can be incorporated in a variety of different processing systems. The processing apparatus  1  illustrated in FIGS. 1 and 2 is merely exemplary. The wafer carrier  12  of the preferred embodiments, however, is especially advantageous in processing systems such as that of FIGS. 1 and 2, in which the wafer carriers are transported within the housing  2 . 
     Although the invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.