Abstract:
An adjustable wafer transfer machine that includes an adjusting mechanism for changing the spacing between adjacent wafers to accommodate placement of the wafers in either a smaller wafer carrier or a larger wafer carrier and a transfer mechanism for transferring the wafers between the smaller wafer carrier and the adjusting mechanism and for transferring the wafers between the larger wafer carrier and the adjusting mechanism. The adjusting mechanism comprises a pair of flat plates disposed parallel to and opposite one another and a plurality of elongated opposing dividers slidably mounted on the plates. The dividers are disposed vertically adjacent to one another at spaced apart intervals and they extend horizontally to support the wafers along a portion of their perimeter. A positioning mechanism is operatively coupled to the dividers for changing the spacing between the dividers and, correspondingly, between the wafers supported on the dividers.

Description:
This application is a division of application Ser. No. 08/649,942, filed May 14, 1996, now U.S. Pat. No. 5,735,662. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to semiconductor manufacturing equipment and, more particularly, to wafer transfer machines. 
     BACKGROUND OF THE INVENTION 
     Generally, semiconductor devices are mass produced by forming many identical circuit patterns on a single silicon wafer which is thereafter cut into many identical dies or “chips.” Semiconductor devices, also commonly referred to as integrated circuits, are typically constructed by successively depositing or “stacking” layers of various materials on the wafer. Each layer is patterned as necessary to form the desired circuit components. To ensure reliable and predictable operation of integrated circuits, the wafer and deposited materials must be free from contamination. Hence, many fabrication processes must be performed in an environment that is essentially free from contamination. For example, the contamination level requirement for Class  1  cleanliness in semiconductor wafer processing areas or “clean rooms” is less than one part (contaminates) per cubic foot. To achieve this high degree of cleanliness, special high volume ventilation systems are used to continuously filter the air. These systems represent a significant contribution to the overall cost of manufacturing semiconductor devices. Accordingly, substantial cost savings can be realized by minimizing the size of the clean rooms and by making the most efficient use of all available clean room space. 
     A number of different size wafers, ranging from 3 inches in diameter to 8 inches in diameter, are currently produced in the semiconductor industry. In addition, development efforts are underway to produce 10 and 12 inch diameter wafers. While it is economically desirable to have the capability to produce wafers of all sizes, each size wafer generally requires its own special processing equipment. The redundancy in equipment to process different size wafers increases equipment costs as well as the size of the clean room and the associated construction and maintenance costs. Cost and space savings could be realized if some of the same equipment could be used to process different size wafers. 
     During the manufacture of semiconductor devices, the wafers are subjected to a number of different processes and environmental conditions. Wafer carriers, sometimes also called cassettes or “boats,” are used to house the wafers for processing, bulk storing and transporting through the manufacturing processes. One type of wafer carrier is not typically suitable for exposure to all of the different environmental conditions encountered during processing. As a result, the wafers have to be transferred between different types of boats at various times during the production of the semiconductor devices. Wafer transfer machines are used to perform this task. Conventional wafer transfer machines are capable of transferring only one size wafer to and from only one size wafer carrier. It would be advantageous in reducing manufacturing costs to process smaller diameter wafers in larger diameter wafer processing machines. For example, it is desirable to process six inch wafers using eight inch processing machines. Thus, there is a need for a wafer transfer machine that is capable of transferring six inch diameter wafers to and from eight inch diameter wafer carriers to facilitate processing the six inch wafers in eight inch machines. One problem associated with such a transfer, however, is the disparate wafer to wafer spacing in six inch and eight inch wafer carriers. That is, the wafer to wafer spacing is {fraction (3/16)} inch in six inch wafer carriers and ¼ inch in eight inch wafer carriers. What is needed is a wafer transfer machine that can adjust the wafer to wafer spacing to accommodate the use of both six inch and eight inch wafer carriers. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is one object of the invention to facilitate the utilization of eight inch wafer processing machines to process six inch wafers. It is another object to reduce the number of machines necessary to support the processing of different size wafers, particularly in a clean room environment. It is a further object of the invention to reduce the equipment and associated clean room costs for the manufacture of semiconductor devices. It is yet another object of the invention to transfer smaller diameter wafers, typically six inch wafers, to and from a larger diameter wafer carrier, typically an eight inch wafer carrier. 
     These and other objects and advantages may be achieved by a novel apparatus for adjusting the spacing between a series of semiconductor wafers or other such planar objects aligned parallel to one another. The apparatus includes a pair of flat plates disposed parallel to and opposite one another. The plates are spaced apart a distance sufficient to allow the horizontal passage of the objects therebetween. A plurality of elongated opposing dividers are slidably mounted on the plates. The dividers are disposed vertically adjacent to one another at spaced apart intervals and they extend horizontally to support the objects along a portion of their perimeter. A positioning mechanism is operatively coupled to the dividers for changing the spacing between the dividers. The positioning mechanism is operative between a first position wherein the dividers are vertically spaced apart a first distance and a second position wherein the dividers are vertically spaced apart a second distance greater than the first distance. Thus, the spacing between the objects may be changed by moving the positioning mechanism alternately between the first and second positions. 
     In one preferred version of this spacing adapter apparatus, the positioning mechanism comprises a series of vertically oriented slots in the plates. Each divider is slidably mounted in a respective one of the slots. The first slot has a length L 1  and each succeeding slot has a length L n  computed according to the equation L n =L n−1 +ΔD, where L n−1  is the length of the immediately preceding slot and ΔD is the difference between the first distance and the second distance. The spacing between the objects is changed in this version of the invention by moving the dividers up and down in the slots. 
     Another aspect of the invention provides an adjustable wafer transfer machine that allows wafers to be transferred between smaller and larger wafer carriers. The adjustable wafer transfer machine of the present invention includes (1) an adjusting mechanism for changing the spacing between adjacent wafers to accommodate placement of the wafers in either a smaller wafer carrier or a larger wafer carrier, and (2) a transfer mechanism for transferring the wafers between the smaller wafer carrier and the adjusting mechanism and for transferring the wafers between the larger wafer carrier and the adjusting mechanism. In one preferred version of this aspect of the invention, the adjusting mechanism constitutes the spacing adapter apparatus described above. In another preferred version of this aspect of the invention, the transfer mechanism includes a turntable assembly and two transfer arms. The turntable assembly consists of a turntable rotatably mounted on a base. The turntable has a first portion and a second portion. The first portion has an upper surface for receiving the wafer carriers. The adjusting mechanism, such as the preferred spacing adapter, is operatively coupled to the second portion of the turntable. The first transfer arm is positioned adjacent to one end of the turntable and the second transfer arm is positioned adjacent to the other end of the turntable. The turntable is operable to rotate between a first position and a second position. When the turntable is in the first position, the first portion of the turntable (which receives the wafer carriers) is adjacent to the first transfer arm and the second portion of the turntable (on which the adjusting mechanism is mounted) is positioned adjacent to the second transfer arm. When the turntable is in the second position, the first portion of the turntable is adjacent to the second transfer arm and the second portion of the turntable is adjacent to the first transfer arm. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded isometric view of the presently preferred embodiment of the adjustable wafer transfer machine. 
     FIG. 2 is an elevation view of the spacing adapter of the adjustable wafer transfer machine of FIG. 1 configured to receive wafers from a smaller wafer carrier. 
     FIG. 3 is an elevation view of the spacing adapter of the adjustable wafer transfer machine of FIG. 1 configured to increase the spacing between wafers for transferring the wafers into a larger wafer carrier. 
     FIG. 4 is an isometric view of the adjustable wafer transfer machine of FIG. 1 with a smaller wafer carrier installed on the turntable for transferring the wafers from the smaller wafer carrier into the spacing adapter. 
     FIG. 4A is a detail isometric view of a portion the wafer dividers disposed along the inner surface of the spacing adapter shown in FIG.  4 . 
     FIG. 5 is a detail isometric view of the spacing adapter configured to receive wafers from or transfer wafers to a smaller wafer carrier. 
     FIG. 6 is an isometric view of the adjustable wafer transfer machine of FIG. 1 with a larger wafer carrier installed on the turntable for transferring the wafers from the spacing adapter into the larger wafer carrier. 
     FIG. 6A is a detail isometric view of a portion the wafer dividers disposed along the inner surface of the spacing adapter shown in FIG.  6 . 
     FIG. 7 is an isometric view of the adjustable wafer transfer machine of FIG. 1 with a larger wafer carrier installed on the turntable for transferring the wafers from the larger wafer carrier into the spacing adapter. 
     FIGS. 8 and 9 are isometric views of an alternative embodiment of the wafer transfer machine wherein the spacing adapter is mounted on a fixed base plate. Transfer plates removably attached to the transfer arms are provided to accommodate the different size wafer carriers. FIG. 8 shows the machine configured to transfer the wafers from a smaller wafer carrier into the spacing adapter and from the spacing adapter into a larger wafer carrier. FIG. 9 shows the machine configured to transfer the wafers from a larger wafer carrier into the spacing adapter and from the spacing adapter into a smaller wafer carrier. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 and 4, adjustable wafer transfer machine  10  includes a spacing adapter  12  mounted on a turntable assembly  14 . Turntable assembly  14  consists of a turntable  24  mounted on a base  46 . The component parts of spacing adapter  12  will now be described with reference to FIGS. 1-5. A pair of guide plates  16  are positioned opposite one another on each side of turntable assembly  14 . Guide plates  16  are constructed as flat rectangular plates having an inner surface  16   a,  an outer surface  16   b,  and a flange like projection  16   c.  Guide plates  16  are attached to guide rods  18  through pillow blocks  20 . Preferably, the bore of each pillow block  20  is fitted with a bushing, linear bearing or the like to better allow guide plates  16  to slide up and down on guide rods  18 . Also preferably, there are four pillow blocks  20  attached to guide plates  16  at or near the corners of guide plates  16 . Saddle member  22  is mounted on turntable  24 . The lower ends  18   a  of guide rods  18  are attached to saddle member  22 . Alternatively, to achieve more stability lower ends  18   a  of guide rods  18  may be extended through saddle member  22  and threaded into turntable  24 . The upper ends  18   b  of guide rods are fastened to top frame member  26 . Thus, guide rods  18  are fixed in a vertical orientation. As will be apparent to those skilled in the art, various other means and configurations for mounting guide rods  18  are possible. All that is required is that guide rods  18  be made sufficiently rigid to maintain a substantially vertical orientation under load during wafer transfer operations. 
     A series of wafer dividers  28  extend along and project inwardly from the inner surfaces  16   a  of guide plates  16 . Dividers  28  support the wafers along a portion of the perimeter of each wafer in essentially the same way the wafers are held in a conventional wafer carrier. To better illustrate the various features of the invention, only one divider is shown in FIG. 1. A typical wafer carrier holds up to twenty five wafers. Hence, twenty five dividers  28  would ordinarily be used. Dividers  28  are constructed as elongated bars having wedge shaped projections in opposing alignment with one another. Each divider  28  has a corresponding optional counterweight  30 . Counterweights  30  are positioned on the outer surfaces  16   b  of guide plates  16  opposite the corresponding divider. Dividers  28  are mounted through vertical slots  32  in guide plates  16  to counterweights  30  by pins  34 . Thus, pins  34  extend through slots  32  between dividers  28  and counterweights  30 . Pins  34  may be any suitable fastener, such as a shoulder bolt, that will slide in slots  32  after dividers  28  are mounted to counterweights  30 . Each counterweight  30  weighs approximately the same as each divider  28  so that pins  34  slide up and down in slots  32  without binding. Preferably, counterweights  30  are constructed as elongated bars. In this way, dividers  28  are made to move smoothly and evenly up and down as guide plates  16  are raised and lowered. 
     Lift rod  36  extends through holes  38  in projection  16   c  of guide plates  16  between lift cams  40 . Preferably, holes  38  are fitted with a bushing, bearing or the like to better allow lift rod  36  to turn in holes  38 . Each lift cam  40  has a circumferential contact perimeter  40   a  that rotates on a pair of rollers  42  mounted in the flange portion  22   a  of saddle member  22 , as best seen in FIGS. 2 and 3. Alternatively, contact perimeter  40   a  may rotate directly on flange portion  22   a.  Rollers  42  are preferred to allow lift cams  40  to rotate easily and to minimize wear on the contact surfaces and thereby reduce the risk of particulate contamination of the semiconductor wafers. The ends  36   a  and  36   b  of lift rod  36  are attached to lift cams  40  at a point off center to provide for a camming action as the lift cams  40  are rotated. Thus, guide plates  16  can be raised and lowered by rotating lift cams  40 . Other configurations or mechanism to raise and lower guide plates  16  are possible. For example, lift cams  40  may be constructed to have an oblong perimeter (i.e., a lobe), in which case lift rod  36  attaches to the center of lift cams  40 , to achieve the necessary camming action as the lift cams are rotated. The camming mechanism described could be omitted and the guide plates  16  raised and lowered simply by lifting and releasing lift rod  36 . Alternatively, the dividers/counterweights could be raised and lowered. Lift cams  40  are sized and shaped as necessary to cause guide plates  16  to move vertically at least the distance equal to the length of the longest of the vertical slots  32 . The camming action to raise and lower guide plates  16  is initiated by rotating handle  44 , which is attached to one of the lift cams. Preferably, handle  44  includes a lever portion  44   a  and a knob portion  44   b.  Also preferably, lift rod  36  is keyed to lift cams  40  so that both cams rotate upon rotation of handle  44 . 
     Turntable assembly  14  includes a base  46  and a turntable  24 . Turntable  24  of turntable assembly  14  is, preferably, shaped like a segmented disc having circular outer perimeter ends  24   a.  Turntable  24  includes an upper surface  48 . Upper surface  48  is divided into a first portion  50 , upon which wafer carriers are placed during transfer operations, and a second portion  52  upon which saddle member  22  is mounted. Turntable  24  is pivotally mounted in base  46 . Preferably, base  46  is recessed so that the upper surface of base  46  is flush with the first portion  50  of upper surface  48  of turntable  24 . Base  46  also preferably includes circular recessed sidewalls  54  that correspond to the circular outer perimeter ends  24   a  of turntable  24 . Turntable  24  pivots about bearing rod  56  with respect to base  46 . Bearing rod  56  is fixedly attached to turntable  24  through bearing rod plate  58 . Bearing rod  56  extends through a hole  60  in base  46  so that turntable  24  can pivot with respect to base  46  by means of bearing rod  56  rotating in hole  60 . Preferably, hole  60  is lined with a bushing or bearing to facilitate the rotation of bearing rod  56  in hole  60 . Also preferably, a bearing is used at the interface of turntable  24  and base  46  to allow turntable  24  to slide easily over base  46 . 
     In operation, a first wafer carrier  70  containing smaller diameter wafers (not shown), typically six inch wafers, is positioned on first portion  50  of upper surface  48 . Wafers are transferred from first carrier  70  to spacing adapter  12  via a first transfer arm  62 . In a standard six inch wafer carrier, the wafers are spaced apart {fraction (3/16)} inch. That is, the wafer to wafer gap is {fraction (3/16)} inch. Thus, guide plates  16  are in the lowered position, so that dividers  28  are positioned at the top of slots  32 , for receiving the wafers from the first smaller diameter wafer carrier  70 . The lower-most dividers are blocked by pads  27  to force dividers  28  to the top of slots  32  when guide plates  16  are in the lowered position. Pads  27  are mounted on saddle member  22  under dividers  28 . Pads  27  are sized as necessary to locate the lower-most divider at the top of the corresponding slot. The remaining dividers are successively stacked one upon the other when guide plates  16  are in the lowered position. Alternatively, pads  27  may be located under counterweights  30  to achieve the same blocking and stacking effect of dividers  28 . 
     Once the wafers have been transferred into the spacing adapter  12 , they are repositioned by raising guide plates  16 . Guide plates  16  are raised by rotating handle  44 , as best seen by comparing FIGS. 2 and 3. As handle  44  is rotated, lift rod  36  raises guide plates  16  under the camming action of lift cams  40  turning on rollers  42 . As guide plates  16  are raised, dividers  28  and counterweights  30  fall to the bottom of slots  32 . Thus, the spacing between wafers is increased as required to accommodate transfer of the smaller diameter wafers into a second wafer carrier for larger diameter wafers, typically eight inch wafers. In a standard eight inch wafer carrier, the wafers are spaced apart ¼ inch. That is, the spacing between wafers is ¼ inch. 
     The pattern of slots  32  required to reposition twenty five wafers from a wafer to wafer gap of {fraction (3/16)} inch to a wafer to wafer gap of ¼ inch (and from ¼ to {fraction (3/16)} inch) is illustrated in FIGS. 2 and 3. Slots  32   a - 32   y  are disposed in a staggered configuration so that the distance between the top of each slot and the immediately preceding slot is {fraction (3/16)} inch. Slot  32   a,  corresponding to the top wafer in a fully loaded wafer carrier, has a length of zero. Thus, the divider held in slot  32   a  moves the full range of guide plates  16  as they are raised and lowered. Each succeeding slot  32   b - 32   y  is {fraction (1/16)} inches longer than the preceding slot. Slot  32   y,  corresponding to the bottom wafer in a fully loaded wafer carrier, is 1½ inches long. Thus, the divider held in slot  32   y  remains essentially stationary as guide plates  16  are raised and lowered. In general, the first/top slot has a length L 1  and each succeeding slot has a length L n  computed according to the equation L n =L n−1 +ΔD, where L n−1  is the length of the immediately preceding slot and ΔD is the change in wafer to wafer gap spacing between the smaller and larger wafer carriers. 
     Referring to FIG. 6, once the wafers have been repositioned to achieve the desired wafer to wafer gap spacing, the wafers are transferred from spacing adapter  12  to second wafer carrier  74  via second transfer arm  64 . 
     Turntable assembly  14  is used to reverse the process to transfer wafers from second wafer carrier  74  to the smaller diameter first wafer carrier  70 . Referring to FIG. 7, turntable  24  is rotated 180° so that first portion  50  of upper surface  48  is adjacent to second transfer arm  62 . Second wafer carrier  74  is positioned on first portion  50  of upper surface  48  of turntable  24 . The wafers are transferred from second carrier  74  to spacing adapter  12  via second transfer arm  64 . Once the wafers have been transferred into the spacing adapter  12 , second carrier  74  is removed and the wafers are repositioned by lowering guide plates  16 . Guide plates  16  are lowered by rotating handle  44 , as best seen by comparing FIGS. 3 and 2. As handle  44  is rotated, lift rod  36  lowers guide plates  16  under the camming action of lift cams  40  turning on rollers  42 . As guide plates  16  are lowered, the lower-most dividers are blocked by pads  27  to force dividers  28  and counterweights  30  to the top of slots  32 . Thus, the wafer to wafer gap is decreased as required to accommodate the transfer of the wafers into the smaller diameter first wafer carrier  70 . Once the wafers have been repositioned to achieve the desired wafer to wafer gap spacing, the wafers are transferred from spacing adapter  12  to first wafer carrier  70  via first transfer arm  62 . 
     Referring again to FIGS. 1 and 4, transfer arms  62  and  64  each have a transfer end  62   a,    64   a  and a translation end  62   b,    64   b.  The translation of transfer arms  62 ,  64  is by means of slide rods  80 . One end of slide rods  80  is attached to the translation ends  62   b,    64   b  of transfer arms  62 ,  64 . The other end of slide rods  80  is attached to slide blocks  82 . Slide blocks  82  are mounted on and slide along slide rails  84 . Slide rails  84  are mounted parallel to the longitudinal axis of turntable assembly  14  between two pairs of legs  86 ,  87  and  88 ,  89 . Legs  86 - 89  are mounted to the bottom of base  46 . Preferably, legs  86 - 89  are positioned on base  46  to block the movement of slide blocks  82  and thereby limit the range of motion of transfer arms  62 ,  64 . 
     As will be apparent to those skilled in the art, the inside dimensions of a standard eight inch wafer carrier should modified to conform to the size of a six inch wafer to allow the carrier to receive and hold six inch wafers. 
     In an alternative embodiment illustrated in FIGS. 8 and 9, spacing adapter  12  is mounted on a stationary base plate  90 , rather than on the turntable assembly of the previously described embodiment. Transfer plates  92 ,  94  are provided to accommodate different size wafer carriers. Transfer plates  92 ,  94  are removably attached to transfer ends  62   a,    64   a  of transfer arms  62 ,  64  to change the overall length of wafer contact surface  96  appropriate for a particular size wafer carrier. As shown in FIG. 8, transfer plate  92  is installed on first transfer arm  62  to transfer wafers from a smaller diameter wafer carrier into spacing adapter  12 . Transfer plate  94 , which is taller and wider than transfer plate  92 , is installed on second transfer arm  64  to transfer the wafers from spacing adapter  12  into a larger diameter wafer carrier. To reverse the process, transfer plates  94  are installed on first transfer arm  62  to transfer the wafers from a larger diameter wafer carrier into spacing adapter  12 . Transfer plates  92  are installed on second transfer arm  64  to transfer the wafers from spacing adapter  12  into a smaller diameter wafer carrier. 
     Wafer transfer machine  10  also preferably includes a lock  66  that prevents any unintended rotation of turntable  24 . Lock  66  represents generally any suitable locking mechanism such as a spring loaded retractable piece that extends into a corresponding recess in one or both ends  24   a  of turntable  24 . 
     Conventional bearings may be used for all moving parts to minimize surface wear. For example, pillow blocks  20  are linear pillow block bearing assembly, such as a Berg model LPA-1. The lift bearings that support lift rods  36  are single row flanged ball bearings, such as a Berg model B2-22-S-Q3. The bearing rod bearing, which is seated in hole  60 , is a single row, unshielded, unflanged ball bearing, such as a Berg model B10-4. Preferably, the bearing rod bearing is used together with a thrust bearing, such as a Berg model B5-8-SS, located under bearing rod plate  58 . Other conventional bearings may be substituted for those mentioned. The structural components of the adjustable wafer transfer machine may be made of any suitable structurally stable corrosion resistant material, such as polypropylene, aluminum or stainless steel. Bearing surface materials are preferably made of stainless steel to minimize the risk of contaminating the wafers and to reduce wear on the contact surfaces. 
     While there is shown and described the preferred embodiment of the invention, it is to be understood that this invention is not limited thereto but may be variously embodied to practice within the scope of the following claims.