Abstract:
A plastic insert ( 20 ) is configured to provide support of thin wafers ( 49 ) in wafer carriers ( 45 ) configured to provide peripheral wafer support. The invention includes the insert, the insert in combination with a wafer carrier, and the, methods of supporting the thin wafers as provided by the insert and the wafer carrier. The insert ( 20 ), in preferred embodiments, utilize tabs ( 80, 82 ) that fit into the side wall recesses ( 53 ) and have an interference fit in said recesses to secure the insert in place.

Description:
This application claims the benefit under 35 U.S.C 119(e) of U.S. Provisional Application No. 60/280,774, filed on Apr. 1, 2001. Said application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to wafer carriers, more particularly the invention relates to apparatus and methods for thin wafers. 
     BACKGROUND OF THE INVENTION 
     Integrated circuits are manufactured from crystalline wafers, typically silicon wafers. These wafers are subjected to numerous processing steps in highly controlled environmental conditions. The wafers are extremely fragile and vulnerable to damage and contamination. The wafers are typically round in shape and are transported, stored, and processed in wafer carriers of various types. Wafer carriers are typically formed of plastic and will generally have a machine interface that provides precise positioning of the wafer carrier on equipment. A common wafer carrier utilized in semiconductor fabrication facilities is the H-bar wafer carrier. This carrier has an open front, or top depending on the orientation, a pair of sidewalls, and a pair of endwalls. One of the endwalls has an H-bar machine interface. Wafers are inserted and withdrawn through the open front from a plurality of slots defined by recesses on the inside of the carrier sidewalls. The recesses are defined by projections extending generally toward the opposite sidewall. The projections may be configured as teeth. For conventional wafers the carriers typically support and restrain the wafers at their peripheral edges. 
     Conventional wafers are 0.030 inches thick. As industry has striven to make electronic devices smaller, integrated circuits have become denser, smaller, and thinner. Integrated circuits are now being manufactured from thin wafers having a thickness of 0.007 in. 
     Robotic means are generally utilized for handling and processing of the individual silicon wafers into the integrated circuit chips including the insertion and withdrawal of the wafers from carriers. Intermediate processing steps the wafers are typically supported in H-bar wafer carriers and individual wafers are withdrawn and inserted by transfer equipment with robotic arms. The set up of the transfer equipment is highly critical so that the wafers are properly grasped and not damaged during any such transfers. To the extent possible, for economic reasons, it is desirable to utilize the same processing equipment and the same set up for the transfer equipment, when then wafers are utilized as opposed to be conventional wafers. 
     Generally semiconductor fabrication facilities are now being set up for 200 or 300 mm wafers. In that the thin wafers are substantially more fragile and less rigid than the conventional wafers, when such wafers are peripherally supported in conventional wafer carriers, the wafers bow downwardly in the middle of the wafer due into gravity. This requires modification of the wafer transfer equipment to accommodate said bowing and prevent damage to the wafer. It would be desirable to be able to utilize conventional wafer carriers such as H-bar wafer carriers and not have to reconfigure the transfer equipment when thin wafers are being processed 
     SUMMARY OF THE INVENTION 
     A plastic insert is configured to provide support of thin wafers in wafer carriers configured to provide peripheral wafer support. The invention includes the insert, the insert in combination with a wafer carrier, and the methods of supporting the thin wafers as provided by the insert and the wafer carrier. The inserts, in preferred embodiments, utilize tabs that fit into recesses formed in the side of a carrier and have a frictional fit in said recesses to secure the insert in place. In preferred embodiments the inserts have a top surface with a plurality of wafer supports positioned inwardly from the wafer periphery for supporting the wafers with minimal contact. In preferred embodiments the insert has a lower surface having strengthening structure providing rigidity to the insert. The top surface ribs may preferably be oriented parallel to the insertion and withdrawal direction of the wafers and extend upwardly to position the supported wafer in the slot immediately above the slot defined by the recesses in which the tabs are positioned. Thus, the inserts may be inserted into alternate slots in the carrier. The insert, in preferred embodiments may have an h-shape offering an optimal combination of support of each wafer and precise positioning of the wafer while minimizing the amount of plastic and correspondingly the weight of the insert. 
     Thus, the invention may be characterized as a wafer carrier and insert for supporting at least one thin wafer therein. The wafer carrier has a carrier portion having at least a top, a bottom, a pair of opposing sides, and an open front. The pair of opposing sides has a plurality of opposing ribs defining a plurality of slots. The insert is adapted to fit one of the slots and comprises a plate. The plate has a pair of side margins with a plurality of projecting tab structures that are adapted to frictionally engage the surfaces within the recess forming the slot. The plate has a plurality of wafer supports projecting upwardly which are adapted to support a thin wafer above the insert with a portion of the periphery of the wafer within the slot immediately above the slot in which the insert is located. The wafer supports may be configured so that a robotic wafer handling member is insertable between said insert and the wafer. The insert may have a bottom surface with stiffening ribs formed therein. Each of the tab structures may be spring biased against the surface engaged by the tab, and the direction of the bias may alternate between adjacent tabs. In addition, the wafer supports may project into the slot wherein the wafer is held for a distance of at least half of the height of the slot so that back-and-forth movement of the wafer within the slot is minimized when the wafer carrier is oriented with the open front of the carrier upward. 
     The invention may also be characterized as a wafer carrier and insert for supporting at least one thin wafer therein, and wherein the insert is a plate having means for engaging the opposing sides of the carrier so that the plate is supported intermediate the opposing sides. The plate has means for supporting a thin wafer above the top surface of the plate, which may be adapted so as to allow a robotic wafer handling member to be interposed between the insert and a thin wafer resting on the wafer supports. 
     The invention may also be characterized as an insert for supporting a thin wafer in a wafer carrier. The wafer carrier has an open front with an insertion and withdrawal direction, a pair of sidewalls, a top and a bottom. The sidewalls have a plurality of recess pairs defining a plurality of slots, and the bottom has an interference fit for precise positioning of the carrier with respect to a corresponding receiver. The insert has a pair of recess engaging portions that are configured to engage a recess pair of the wafer carrier. Further, the insert has an upper surface with a plurality of upwardly extending protrusions to provide contact with a wafer. 
     The invention may also be characterized as a method for supporting at least one thin wafer in a wafer carrier. The method has the steps of providing a wafer carrier having at least a top, a bottom, a pair of opposing sides, and an open front, the pair of opposing sides having a plurality of opposing recesses defining a plurality of slots; forming a planar insert having a top surface, the insert being adapted to fit in one of said plurality of slots and having wafer supports for supporting a thin wafer above said top surface with a portion of the periphery of the wafer within a separate one of said plurality of slots; placing said insert in one of said plurality of slots; and resting a thin wafer on the wafer supports of said insert. 
     A feature and advantage of particular embodiments of the invention is that the inserts may be securely attached in the wafer carrier by utilizing the tabs as integral retainer springs. The tabs may alternate with one bearing against the respective upward projection and the next bearing against the respective lower projection. The row of tabs preferably extends substantially the length of each recess. The alternating tabs and the extension of the tabs the length of each of the respective recesses, provides a precise positioning means for the insert with respect to the carrier thereby precisely positioning the supported wafer. 
     A feature and advantage of the invention is that thin wafers of approximately 0.007 inches in thickness may be supported in conventional wafer carriers. 
     Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a wafer carrier and insert in accordance with the present invention. 
         FIG. 2  is a perspective view of the top of a currently most preferred embodiment of an insert in accordance with the invention. 
         FIG. 3  is a perspective view of the bottom of an insert in accordance with the invention. 
         FIG. 4  is a perspective view of the top of another embodiment of an insert in accordance with the invention 
         FIG. 5  is a top plan view of the insert of  FIGS. 2 and 3 . 
         FIG. 6  is a front cross-sectional view of the insert of  FIGS. 2 ,  3  and  5 , shown inserted in a wafer carrier. 
         FIG. 7  is a cross-sectional view of a portion of the insert of  FIGS. 2 ,  3 ,  5  and  6 , and taken at line  6 — 6  of  FIG. 5 . 
         FIG. 8  is a cross-sectional view of a portion of an alternative embodiment of the insert of  FIGS. 2 ,  3 ,  5  and  6 , and taken at line  6 — 6  of  FIG. 5 . 
         FIG. 9  is a perspective view of the wafer carrier and insert of the present invention in place on automatic processing equipment and with a robotic wafer handling arm assembly. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The accompanying Figures depict embodiments of the wafer container of the present invention, and features and components thereof. Any references to front and back, right and left, top and bottom, upper and lower, and horizontal and vertical are intended for convenience of description, not to limit the present invention or its components to any one positional or spacial orientation. Any dimensions specified in the attached Figures and this specification may vary with a potential design and the intended use of an embodiment of the invention without departing from the scope of the invention. 
     Referring now to  FIG. 1 , an H-bar wafer carrier  45  and insert  20  in accordance with the present invention is shown supporting a thin wafer  49 . The wafer carrier has a plurality of ribs  50  defining pairs  52  of recesses  53 , with one of the pair of recesses on the left side  56  and the corresponding other recess on a right side  58 . The H-bar wafer carrier also has a pair of ends  62  and  64 , which, when the carrier is oriented as shown in  FIG. 1 , constitute a top  66  and a bottom  68 . Top  66 , bottom  68 , left side  56  and right side  58  define an open front  72  for insertion and removal of wafers in a direction indicated by the double arrow  75 . Each recess pair defines a wafer slot  76  and is configured to receive a wafer from the open front. Bottom  68  may be interference fit 
     In  FIGS. 2 and 3 , a currently most preferred embodiment of an insert in accordance with the invention is shown. Insert  20  is generally planar and has a top surface  24 , a bottom surface  26 , and a pair of peripheral edges configured as recess engaging portions  30  and  32 . The insert is generally H-shaped and has reinforcing structure  38  on the bottom side shaped as stiffening ribs  40  that generally follow the outline of the insert and extend in radial directions and in concentric arcs. This reinforcing structure provides stiffening to the insert. Top surface  24  has wafer supports  120 ,  122 ,  124  and  126 , each projecting upwardly from ribs  44 . Ribs  44  also provide stiffening to insert  20 , and may serve as guides for a robotic wafer handling tool (not shown). Wafer supports  120 ,  122 ,  124  and  126 , are disposed so that the wafer is supported at multiple points inward of the periphery of the wafer. It is currently most preferred that the wafer contact area of wafer supports  120 ,  122 ,  124 , and  126  be minimized as shown so as to minimize friction and dragging against the wafer surface when a wafer is inserted and withdrawn from the carrier. Other embodiments having a larger contact area, however, such as is shown in  FIG. 4 , may also be used. The insert as illustrated is preferably injected molded of a rigid and resilient plastic such polycarbonate, but may be formed from any suitable and compatible material. 
     In the embodiment illustrated in  FIGS. 2 and 3 , recess engaging portions  30  and  32  are located at the side margins or plate  21  and have tab structures which alternate between a high tab  80  and a low tab  82 . When installed in a wafer carrier, high tabs  80  are in frictional contact with a top surface  86  and low tabs  82  are in frictional contact with bottom surface  88  of recess  53  as best illustrated in  FIGS. 6 and 7 . High tabs  80  and low tabs  82  are placed so as to extend substantially the length of each recess  53 . End tabs  90  have frictional surfaces on both the top and bottom. Also, high tabs  80  and low tabs  82  are configured so that when insert  20  is installed in the recesses  53  of a wafer carrier, high tabs  80  and low tabs  82  are slightly compressed so as to exert a biasing force toward the surface in recess  53  with which they are in contact. This spring bias serves to increase the amount of friction between high tabs  80  and low tabs  82  and the surfaces of recess  53 , and assists in more firmly securing insert  20  within the wafer carrier while still allowing removal of the insert for cleaning purposes. The alternating direction of the biasing force between adjacent tabs serves to more accurately center insert  20  in recess  53 . 
     Referring now to  FIGS. 1 ,  2 ,  6  and  7 , it will be appreciated by those of skill in the art that the configuration of insert  20 , and particularly the placement and configuration of wafer supports  120 ,  122 ,  124  and  126  provides certain unique features and advantages. The height of wafer supports  120 ,  122 ,  124  and  126  may be selected so as to allow a robotic wafer handling tool  200 , such as is shown in  FIG. 9 , to be inserted between top surface  24  of insert  20  and wafer  49 . It is preferred that the height of the wafer supports be selected so that a wafer  49  resting on the supports has a portion of its periphery within the slot  76  located immediately adjacent and above the slot in which insert  20  is located. Also, it is most preferred that the wafer supports  120 ,  122 ,  124  and  126  project into the immediately adjacent slot for at least one-half of the height of the slot, where the height of each slot is defined as the vertical distance between adjacent ends  112  and  114  of ribs  50 . Such projection is preferred so that when wafer carrier  45  is oriented with open front  72  facing upward, a thin wafer  49  disposed in the immediately adjacent slot to the insert will be allowed a minimal amount of clearance for back-and-forth movement in the slot. Those of skill will of course recognize that when the height of wafer supports  120 ,  122 ,  124  and  126  is selected as described, a wafer carrier that is designed to carry  25  normal size wafers, will, with the maximum number of inserts positioned in every other slot, have a capacity of 12 thin wafers. In addition, those of skill will recognize that the placement of wafer supports  120 ,  122 ,  124  and  126  in the locations shown and with ribs  44  oriented front-to-back along the insert, allows the insert to be used with a variety of configurations of robotic wafer handling tools. For example, a forked tool  200  as shown in  FIG. 9  may be inserted so that one branch  204  of the fork fits between wafer supports  120  and  122  and the other branch  202  of the fork fits between wafer supports  124  and  126 . Alternatively, a robotic wafer handling tool having a single contact member may be inserted between wafer supports  122  and  126 . 
     Another embodiment of an insert according to the present invention is shown in  FIG. 8 . A slightly different insert attachment means is used in which the tabs are replaced by radially projecting bifurcate members  92  which engage a rib  50  between the furcations. Again, upwardly extending wafer support structure  124  is provided, and may be nubs for point contact or ribs for line contact. These inserts may be attached to sequential pairs of ribs allowing a wafer to be supported in each slot of the carrier, or in alternate slots allowing more clearance for access to the wafer with a robotic wafer handling tool. 
     Those of skill in the art will recognize that although an H-Bar wafer carrier is described above as receiving the inserts, other carriers, such as transport modules as illustrated in U.S. Pat. Nos. 5,915,562 and 5,944,194, which are incorporated herein by reference, may also be used and are within the scope of the invention. 
     Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of the invention. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.