Abstract:
A wafer transport cart comprises a wheeled support structure and an upright member which is pivotably coupled to the support structure. The upright member has a handle which is pivotably coupled to a wafer cassette support, which comprises a pair of fork-like arms. Wafer production personnel can maneuver the cart adjacent a wafer manufacturing load port, and unload a wafer cassette from the cart to the load port or vice versa, by employing movements of the upright member and the handle. Shock-absorbing dampers are provided for the upright member and the handle. An inter-cart coupling mechanism enables a plurality of carts to be joined together for tandem transport within the manufacturing facility. The arms mate with mating regions on the wafer cassette and on the load port. An alignment notch mates with an alignment pin on the load port. Also described are methods of using the wafer transport cart to load and unload a wafer cassette.

Description:
TECHNICAL FIELD 
     The invention relates to the manufacture of microelectronic circuits and, in particular, to a method and apparatus for transferring wafer cassettes in a microelectronic manufacturing environment. 
     BACKGROUND OF THE INVENTION 
     In the field of microelectronic circuits, manufacturers are increasingly employing very large and heavy wafers, some of which are 300 millimeters in diameter, because they help to lower the cost of production per microelectronic device. Not only are these wafers large and heavy, but they represent relatively expensive material, the more so as a number of time-consuming and complex processing steps are performed upon the wafers. 
     In the semiconductor manufacturing environment partially processed wafers must frequently be transported among storage areas, processing stations, inspection stations, and other stations. 
     In contemporary, high production semiconductor manufacturing environments, large-scale wafers are often stored and transported in wafer cassettes, each of which can hold a plurality of wafers, for example up to two dozen wafers. A fully loaded cassette can weigh ten kilograms or more. 
     Production facilities often have fairly narrow or constricted areas, in which space is at a premium. Thus large, bulky equipment for transporting and storing wafer cassettes is undesirable. 
     Furthermore, time is also at a premium in such production facilities, so equipment used for storing, transporting, loading, and unloading materials such as semiconductor wafers must be easy to use and require a minimum of operator manipulation. 
     Furthermore, equipment used in manufacturing environments which are regulated by federal, state, and local laws and regulations must be safe, stable, and ergonomic. 
     For the reasons stated above, there is a substantial need in the semiconductor manufacturing art for a wafer cassette transport cart and method of use thereof, which are reliable and cost effective, which are safe and easy to use, and which consume a minimum of physical space. 
     SUMMARY 
     In one embodiment, a cart for transporting wafer cassettes is described. The cart comprises a support structure and an upright member pivotably coupled to the support structure. The upright member comprises a handle pivotably coupled to a cassette support. 
     In another embodiment, a method of loading a wafer cassette from a transport cart to a load port is described. The cart includes a wheeled support structure and an upright member pivotably coupled to the support structure. The upright member comprises a cassette support pivotably coupled to a handle. The method comprises moving the cart adjacent the load port, and loading the wafer cassette from the cart to the load port by employing movements of the upright member and the handle. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 illustrates a perspective view of a wafer cassette transport cart and a wafer cassette docking station, in accordance with one embodiment of the invention; 
     FIG. 2 illustrates a side view of damper mount  220  in a first orientation, in accordance with one embodiment of the invention; 
     FIG. 3 illustrates a side view of damper mount  220  in a second orientation, in accordance with one embodiment of the invention; 
     FIG. 4 is one of a sequence of FIGS. 4-7 illustrating the operation of a wafer cassette transport cart, in accordance with one embodiment of the invention; 
     FIG. 5 is one of a sequence of FIGS. 4-7 illustrating the operation of a wafer cassette transport cart, in accordance with one embodiment of the invention; 
     FIG. 6 is one of a sequence of FIGS. 4-7 illustrating the operation of a wafer cassette transport cart, in accordance with one embodiment of the invention; 
     FIG. 7 is one of a sequence of FIGS. 4-7 illustrating the operation of a wafer cassette transport cart, in accordance with one embodiment of the invention; 
     FIG. 8 illustrates a flow diagram of methods for using a wafer cassette transport cart, in accordance with one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
     FIG. 1 illustrates a perspective view of a wafer cassette transport cart  1  and a wafer cassette docking station  50  in accordance with one embodiment of the invention. Wafer cassette transport cart  1  comprises a wheeled support structure  2 . In one embodiment, support structure  2  comprises a set of four wheels  3 ; however, it will be understood by those skilled in the art that the number of wheels is a design choice, and that fewer or more than four wheels could be used. 
     Support structure  2  comprises a front portion, which in FIG. 1 is the portion which is closer to docking port  50 , and support structure  2  further comprises a rear portion, which is the portion which is further from docking port  50 . 
     An upright member  4  is pivotably coupled to the front portion of support structure  2  by a suitable pivot member or hinge structure. In one embodiment the pivot member comprises a pivot pin  7  which passes through an outer front plate  9 , upright member  4 , and an inner front plate  11 . An identical arrangement can be used on the other side of cart  1 , where upright member  4  again is held between plates  9  and  11  by a pivot pin (not shown). It will be understood by those skilled in the art that the upright member  4  can be coupled to other portions of support structure  2  in other embodiments. 
     Upright member  4  is coupled to a pair of dampers  5 , one damper being on either side of cart  1 . Dampers  5  can be of any suitable construction which will dampen motion occurring between upright member  4  and support structure  4 . In one embodiment, dampers  5  are oil-filled hydraulic dampers. It will be understood by those skilled in the art that other types of dampers, such as pneumatic, magnetic, or spring-loaded dampers, could be used. Dampers  5  are employed to lessen jarring or shocking movements which could damage the contents of wafer cassette  10  (shown in phantom outline in FIG. 1 so as not to obscure the details of wafer transport cart  1 ). 
     Handle  6  is coupled to upright member  4  by a pivot rod  12 . In FIG. 1 pivot rod  12  can be seen on the side of cart  1  nearer to the viewer. Pivot rod  12  extends between plates  8  and passes through handle  6 . Handle  6  can pivot upward and downward about pivot rod  12 . 
     Each plate  8  is secured to upright member  4  by an upper U-bolt and a lower U-bolt around upright member  4 . The ends of the U-bolts pass through plate  8  and are secured by cap nuts  21 . 
     A limiter rod  15  extends between plates  8 . Limiter rod  15  is secured against each plate  8  by a screw  26  (only the screw  26  nearer the viewer is shown). Limiter rod  15  can be rigidly fastened to plates  8 , although it need not be. As will be seen in greater detail in FIGS. 2 and 3, which are described below, limiter rod  15  passes through the lower portion of damper mount  220 , which is able to rotate to a limited degree about limiter rod  15 . 
     A wafer cassette support, which comprises a pair of arms  14 , is coupled both to upright member  4  and to handle  6 . Cassette support arms  14  are rotatably coupled to upright member  4  via bar  114 . Bar  114  is secured against each plate  8  by a screw  25  (only the screw  25  nearer the viewer is shown). Bar  114  is free to pivot about screws  25  as cassette support arms  14  are raised and lowered. 
     Cassette support arms  14  are coupled to handle  6  by a pair of coupling members  20 , of which only the coupling member  20  nearer to the viewer is shown. The lower end of each coupling member  20  is pivotably coupled to a lug  13  on the upper surface of the associated cassette support arm  14 . The upper end of each coupling member  20  is pivotably coupled to handle  6  by a suitable attachment (not shown). 
     The geometry and structure of handle  6 , upright member  4 , wafer cassette support arms  14 , and coupling members  20  is such that when handle  6  is depressed, support arms  14  are raised, and when handle  6  is elevated, support arms  14  are lowered. The lift ratio between handle  6  and wafer cassette support arms  14  is approximately 1:3 in one embodiment. 
     Bar  106  extends between opposite ends of handle  6  and is affixed to handle  6 , for example by welding. In one embodiment, bar  106  is rectangular in cross-section, which can be seen more easily in FIGS. 2 and 3. 
     To dampen and minimize jarring movement of the support arms  14  when they are lowered, damper  22  is provided. Damper  22  is affixed to damper mount  220 , which is described in greater detail regarding FIGS. 2 and 3 below. In one embodiment, damper  22  is of the same type as dampers  5 ; however, it will be understood by those skilled in the art that damper  22  can be different from dampers  5 , depending upon the damping requirements of the particular application in which wafer transport cart  1  is used. 
     FIG. 2 illustrates a side view of damper mount  220  in a first orientation, in accordance with one embodiment of the invention. Damper mount  220  has a hole  112  through which limiter rod  15  passes. Limiter rod  15  limits the downward motion of cassette support arms  14 . Damper mount  220  can rotate through a limited arc about limiter rod  15 . 
     A spring  108  is affixed to damper mount  220 . Spring  108  can be of any suitable type. In one embodiment, spring  108  is a leaf spring. Spring  108  presses against pivot rod  12 . In FIG. 2 spring  108  is shown uncompressed. 
     The orientation of damper mount  220  shown in FIG. 2 results after handle  6  (refer to FIG. 1) is depressed far enough to raise bar  106  so that ledge  113  of damper mount  220  slides underneath bar  106  from the compression force of spring  108 . Once bar  106  rests upon ledge  113  of damper mount  220 , it remains there. This locking mechanism causes cassette support arms  14  to be locked in a upward position. Arms  14  are typically locked in an upward position while cart  1  is in motion or in a standby mode. 
     Damper  22  has an end cap  114 . In the side views of FIGS. 2 and 3, end cap  114  is shown partially positioned within a U-shaped or V-shaped recess in damper mount  220 . 
     FIG. 3 illustrates a side view of damper mount  220  in a second orientation, in accordance with one embodiment of the invention. The orientation of damper mount  220  shown in FIG. 3, in which damper mount  220  is rotated slightly counter-clockwise, results after release handle  24  is pulled back far enough to let bar  106  slide off ledge  113  of damper mount  220  onto end cap  114  of damper  22 . This release mechanism causes bar  106  to slowly sink, which in turn dampens the downward movement of cassette support arms  14  (refer to FIG.  1 ). 
     As the release mechanism releases the cassette support to move into a downward position, at the same time spring  108  is depressed. Spring  108  and pivot rod  12  limit the rearward movement of damper mount  220 . 
     Release handle  24  is pulled back when an operator desires to lower the cassette support arms  14 , for example when loading or unloading a wafer cassette  10 . 
     Referring once again to FIG. 1, cassette stop  18  serves to keep cassette  10  from sliding too far back on arms  14 . In one embodiment, cassette stop  18  bridges wafer cassette support arms  14 ; however, it will be understood by those skilled in the art that individual cassette stops could be used on each arm  14 . 
     Arms  14  have areas which facilitate holding the wafer cassette  10 . For example, arms  14  comprise recessed areas  16  which mate with corresponding mating regions of suitable geometric shape on wafer cassette. Arms  14  also comprise raised edge plates  17  which confine the wafer cassette  10  between arms  14 , so that the wafer cassette  10  does not slip sidewise off of either of arms  14 . 
     From the above description of cart  1 , it will be understood that the cassette support arms  14  have a predefined range of motion. That is, they can only be raised or lowered within a certain amount. Likewise, it will be understood that the upright member  4  has a predefined range of motion, in that it can only be moved forward or backward within a certain amount. These limitations on the range of motion of the arms  14  and upright member  4  ensure that the wafer cassette  10  will not fall off as it is being stored on transported using wafer transport cart  1 . 
     Also shown in FIG. 1 is a load port  50  of a piece of semiconductor manufacturing equipment  52 , of which only a portion is illustrated. Depending upon the level of sophistication of the particular piece of equipment  52 , load port  50  can be merely a table-like structure, where wafer cassette is set down for subsequent manual movement, either of individual wafers within the cassette  10  or of the entire cassette  10 . Alternatively, load port  50  can be a robotic station where subsequent movement of individual wafers or of the entire wafer cassette is carried out by automated equipment. 
     Load port  50  comprises mating regions in the form of grooves  54  and alignment pins  56 . Arms  14  of transport cart  1  mate with grooves  54  of load port  50  to assist in aligning wafer cassette  10  on alignment pins  56 . The lower surface of wafer cassette  10  has indents (not illustrated) which suitably mate with alignment pins  56  to maintain wafer cassette  10  in proper position on load port  50 . Alignment pins  56  can have a conical or pointed upper end to facilitate mating with the indents in the lower surface of wafer cassette  10 . 
     At the base of load port  50  is a docking flange  58  which comprises a centering pin  60 . The front portion of support structure  2  of cart  1  comprises a centering bar  42  which has a centering notch  44 . Centering notch  44  of transport cart  1  mates with centering pin  60  of load port  50  to assist in aligning arms  14  with the grooves  54  in the upper surface of load port  50 . 
     In order to facilitate movement of several transport carts  1  through a manufacturing facility simultaneously, the support structure  2  comprises a coupler to couple a first cart to a cart behind it and, if desired, to a cart ahead of it. Thus strings or trains comprising several carts  1  may be moved simultaneously. 
     In one embodiment the coupler comprises a pair of hooks  34  on the front portion of the support structure  2 , and a pair of apertures  32  in a plate  30  on the rear portion of support structure  2 . The hooks  34  at the front of one cart  1  can be operatively engaged with the apertures at the rear of another cart  1 . 
     Hooks  34  pivot about rod  38 . Hooks  34  are raised and lowered by movement of a control lever  40 , to which a control cable or rod (not shown) is coupled. As control lever  40  is first moved in one direction and then another, hooks  34  are raised and lowered. It will be understood by those skilled in the art that other mechanisms could be provided for raising and lowering hooks  34 . For example, with a suitable cam mechanism, they could be raised and lowered by fore and aft movement of upright member  4  relative to support structure  2 . Alternatively, they could be electrically, hydraulically, or pneumatically controlled. 
     FIGS. 4-7 illustrate the operation of a wafer cassette transport cart in accordance with one embodiment of the invention. FIGS. 4-7 depict a sequence of movements by an equipment operator  100  in unloading a wafer cassette  10  at a load port  50 , which is part of semiconductor manufacturing equipment  52 . 
     First, in FIG. 4, operator  100  approaches load port  50  with wafer cassette  10  in an unlocked position on arms  14  of the transport cart. Operator  100  is using the upper portion of upright member  4  to push and maneuver the cart. 
     Next, in FIG. 5, operator  100  momentarily depresses handle  6  while swinging upright member  4  forward toward load port  50 . Operator  100  aims arms  14  for the mating grooves  54  in the upper surface of load port  50 . 
     Next, in FIG. 6, operator  100  has swung upright member  4  forward and has lowered handle  6 , so that arms  14  are in grooves  54 , and the wafer cassette  10  is resting on alignment pins  56  (FIGS. 1,  4 , and  5 ). 
     Finally, in FIG. 7, operator  100  has withdrawn the arms  14  of the cart from grooves  54  (FIGS. 1,  4 , and  5 ) by backing the cart away from load port  50 , leaving the wafer cassette  10  mounted atop load port  50  in the desired orientation. 
     FIG. 8 illustrates a flow diagram of methods for using a wafer cassette transport cart  1  in accordance with one embodiment of the invention. According to one method, the transport cart  1  is used to load a wafer cassette  10  onto a load port  50 . According to another method, the transport cart  1  is used to load a wafer cassette  10  from a load port  50  onto the cart  1 . 
     The method starts in block  101 . 
     In block  103  the cart is moved adjacent to the load port. This can be performed either by a human operator or by robotic equipment. 
     In decision block  105 , a determination is made as to which type of operation is to be performed. If the wafer cassette is to be loaded to the load port, the method proceeds to block  107 , where the cassette is loaded to the load port by employing movements of the upright member  4  and the handle  6 , as shown in FIGS. 4-7. 
     If the cassette is to be unloaded from load port  50 , the method proceeds to block  108 , where the cassette is loaded from the load port  50  to the cart  1 , by essentially reversing the movements depicted in FIGS. 4-7. 
     The method ends in block  110 . 
     In summary, the present invention provides a wafer cassette transport cart and method of use thereof, which are reliable and cost effective, which are safe and easy to use, and which consume a minimum of physical space. 
     It will be apparent to those skilled in the art that the disclosed invention can be modified in numerous ways and can assume many embodiments other than the preferred form specifically set out and described above. 
     Wafer transport cart  1  could be constructed so as to be foldable or collapsible. It could also be constructed to be stackable. 
     The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.