Abstract:
The processing status of a plurality of semiconductor wafers undergoing processing is positively identified by the use of indicator flags associated with cassettes containing the wafers. The flags are moved between at least two processing state indicating positions during processing of the wafers by a robotic arm that also transfers the wafers between the cassettes and a wafer processing station.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to methods and apparatus for semiconductor wafer processing and manufacture of micro-circuit devices, and more particularly to methods and apparatus for positively identifying the processing status of a plurality of semiconductor wafers that are being processed using multi-wafer cassettes as a transport method. 
     2. Background and Description of Related Art 
     As is well known, in semiconductor wafer processing, a semiconductor wafer is treated in a number of processing steps to form a plurality of micro-circuit devices on the wafer. Typically, such processing includes successive steps of chemically treating the semiconductor wafer, applying a photosensitive coating to the substrate surface, imaging a circuit pattern onto the substrate coating at a plurality of locations on the substrate using lithography equipment or the like, treating the exposed coating and then repeating the foregoing steps to build up the micro-circuit devices. Such processing treatment further includes, for example, solder printing processing to form electrical connections on the respective micro-circuit devices formed on the substrate. In order to produce micro-circuit devices in volume, large scale production facilities process hundreds of wafers during such processing. Conventional semiconductor wafer processing systems electronically track the process status with computer system controllers and displays that provide the operator with limited status messages, for example, cassette A, wafer no. 15. However, in the event of a power outage, emergency power-off or system malfunction, the process status information may be lost or corrupted, so that when restarting the system, it is not readily possible to determine the processing state of the various wafers in a cassette, or full cassettes of wafers. 
     SUMMARY OF THE INVENTION 
     The methods and apparatus of the present invention overcome the problems of the prior art and improve the manufacture of micro-circuit devices by providing positive wafer process status identification during semiconductor wafer processing in which a robotic arm moves wafers between a storage cassette located on a cassette holding station and a wafer processing station. The system comprises a mechanical indicator flag movable between at least two, and preferably at least three, processing state indicating positions; and an actuator member connected to the indicator flag and actuated by movement of the robot arm to move the indicator flag. The robot is controlled to move the indicator flag to different processing state indicating positions via the actuator member during the processing according to the stage of the processing and the sensed position of the indicator flag. 
     The wafer process status identification system of the present invention provides a positive, i.e., fool-proof, indication of the processing state of each wafer cassette during the semiconductor wafer processing that allows an operator to immediately determine which cassette or cassettes are finished, which are partially processed and which are awaiting processing. Costs attributed to system status uncertainty during error recovery are reduced, and production efficiency is improved. These and other features and advantages of the invention are described in or are apparent from the following detailed description of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiments of this invention will be described in detail with reference to the following figures, in which like numerals reference like elements, and wherein: 
     FIG. 1 is a plan view of a portion of an exemplary wafer processing system with which the present invention is used; 
     FIG. 2 is a top perspective view of one embodiment of wafer process status indicating apparatus according to the present invention; 
     FIGS. 3 a  and  3   b  are a partial top view and a partial end elevation view, respectively, of a modified version of the embodiment of FIG. 2; and 
     FIG. 4 is a flowchart showing the operation of one embodiment of a positive wafer process status identification system according to the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIG. 1, the positive wafer processing status identification methods and apparatus of the present invention are adapted for use with a conventional wafer processing system  100  comprising at least one wafer cassette holding station or carousel  105  that holds, on a support surface or table  107 , a plurality of, for example, six, separate wafer cassettes  110 ,  120 ,  130 ,  140 ,  150  and  160 . System  100  further comprises a robotic transfer device  170  and process stations  185  and  190 . Process station  185  may be, for example, a centering or pre-alignment station, and station  190  may be a transfer station for loading wafers into a process chamber. The robotic transfer device  170  comprises an articulated arm  172  that terminates in an end effector  174 . End effector  174  advantageously has a first end  174   a  adapted for manipulating wafers, and a second end  174   b  adapted to cooperate with apparatus  200  described below. Articulated arm  172  and end effector  174  have multiple degrees of movement freedom, and arm  172  and end effector  174  are controlled to successively transfer wafers stacked in a cassette located in a transfer position on the carousel  105  between the cassette and the (respective) wafer processing station(s). System  100  and the various components thereof are controlled by one or more controllers (not shown) that also perform various monitoring functions that provide information indicative of the current status of the processing. Typically, the system controllers process this information and generate status and/or alarm messages that are displayed or printed for viewing by a system operator. 
     Referring to FIG. 2, one embodiment of apparatus  200  according to the present invention for providing a positive identification of the processing status of a wafer comprises a semaphore or flag member  211  mounted relative to a support  210  so as to be movable between at least two, and preferably at least three positions respectively indicating different processing states of wafers in an associated cassette. Three positions, for example, can be used to indicate, respectively that processing of the wafers in a cassette i) has not yet started, ii) has started, or iii) has finished. In the illustrated embodiment, flag member  211  is slidably mounted with respect to support  210  so that member  211  is linearly displaced. Alternatively, flag member  211  can be pivotally mounted with respect to support  210  to rotate between different angular orientations or positions indicating different processing states. Advantageously, as shown in FIGS. 2-3 b , support  210  defines a slot in which flag member  211  is slidingly received. The opposite side walls of the support slot are configured to define projecting guide rails  213  that cooperate with recessed tracks  215  formed in the opposing side walls of flag member  211 . Apparatus  200  further comprises spring biasing (not shown) to bias flag member  211  toward one of the processing state indicating positions, and support  210  is configured with detents or the like (not shown) to releasably retain flag member  211  at the other processing state indicating positions when flag member  211  is moved to those positions. 
     As shown, support  210  advantageously is formed as an integral part of carousel table  107 . Alternatively, support  210  is configured as a frame that is attached to carousel table  107  and in which flag  211  is mounted. Support  210  includes a region on which a cassette identifying indicia  212  is displayed, e.g., a numeral as shown, and regions associated with each of the processing state indicating positions of the flag member  211  on which different process state identifying indicia  214 ,  216  and  218  are respectively displayed. Flag member  211  advantageously is also provided with a pointer or other indicia  217 , as shown. Illustrative indicia  214 ,  216 , and  218  for the illustrated three position embodiment are “NEW,” “STARTED,” and “FINISHED” or “COMPLETE”. Advantageously, as shown, the NEW, STARTED and FINISHED positions are arranged so that the NEW position is the radially innermost position, and the FINISHED position is the radially outermost position. It will be appreciated that apparatus  200  can be configured to include an additional flag member movable between a plurality of processing state indicating positions to identify which of the wafers in a cassette is currently being processed. Alternatively, a single flag member could be used having sufficient processing state indicating positions to indicate both the processing state of the entire cassette and which wafer in the cassette is currently being processed. 
     As shown in FIGS. 2 and 3, support  210  is located at the outer peripheral edge of the cassette supporting carousel table  107  adjacent the location where a cassette sits when loaded on the carousel. A separate support and flag member arrangement is mounted at each cassette location on the carousel. Alternatively, the support and flag member arrangement could be disposed on each cassette, or elsewhere on the carousel table as may be convenient. Support  210  can be disposed either vertically or horizontally with respect to the carousel table  107  supporting surface, so that, for example, a slidingly mounted flag member  211  is movable either relatively vertically between a vertically uppermost and a vertically lowermost processing state indicating position, or, as shown, relatively horizontally between a radially outermost and a radially innermost processing state indicating position. 
     Apparatus  200  further comprises actuator apparatus  300  connected to the flag member  211  so as to be actuated manually by an operator, or automatically by movement of the robot arm  172  to move the flag member  211  between its respective processing state indicating positions. As shown in the FIGS. 3 a - 3   b  embodiment, actuator apparatus  300  comprises, for example, an upstanding post  310  on the flag member. With a vertically oriented support member  210 , post  310  advantageously projects outwardly from the face of support member  210  facing the robot arm  172 , so that simple z-axis movement of the robot arm in contact with post  310  displaces flag member  211  upwardly or downwardly. With a horizontally oriented support member, post  310  advantageously projects from either the upper or the lower face of flag member  310 , so that movement of the robot arm to move the end effector  174   b  in a radial direction relative to carousel  105  in contact with post  310  displaces flag member  211  inwardly or outwardly. Alternatively, as shown in the FIG. 2 embodiment, indicia  217  on flag member  211  can be formed on a raised portion of flag member  211  so as to be engageable by end effector  174   b , and thereby constitute the actuator apparatus. It will be appreciated that more complicated actuator apparatus that is responsive to controlled movement of the robot arm can be used. Such actuator apparatus can have, for example, multiple linkages, and/or gear/cam arrangements. 
     Apparatus  200  advantageously further comprises sensor apparatus  400  (schematically shown in FIG. 2) connected to the processing system or robotic controller for determining the processing state indicating position of flag member  211 . Apparatus  400  advantageously comprises contact sensors, such as micro-switches or the like, or non-contact sensor(s) associated with or mounted on support member  210 , or a machine vision system associated with robotic transfer device  170 . 
     Operation of apparatus  200  in accordance with the invention will be described with reference to FIG. 4, which illustrates the operating cycle of a portion of an exemplary wafer processing system, including the initial, or “cold,” start-up, with a cassette carousel empty. At initial start-up (step  402 ), wafer cassettes to be processed are loaded on the carousel table  107  at all cassette positions, and all of the associated flag members  211  are set to the NEW processing state indicating position, either manually or by controlling robot arm  172 . Preferably, apparatus  200  is configured so that flag members  211  are only set to the NEW processing state position manually by the operator, and the robot arm  172  is used to move the flag members only from the NEW position to the other positions. The carousel is then rotated or indexed by one cassette position, and the processing state indicating position of the associated flag member  211  is then sensed (step  404 ). 
     During the first pass through the operating cycle, assuming all of the flag members  211  were correctly set to NEW in step  402 , step  406  is then performed. In step  406 , robot arm  172  is first controlled to move the associated flag member  211  to the STARTED processing state indicating position, and then the robot arm  172  is then automatically controlled to cycle the wafers in the cassette through predetermined wafer processing by transferring successive wafers in the cassette between the cassette and the associated processing station(s). (If the apparatus  200  is configured to also track the processing state of each wafer in a cassette, then the robot arm  172  is controlled, prior to removing the next wafer in a cassette for processing, to move the appropriate flag member to the next position indicating which wafer is being processed.) 
     When all of the wafers in a cassette have been processed, the robot arm  172  is controlled to move the associated flag member  211  to the FINISHED processing state indicating position (step  408 ). During the wafer processing, the operator in step  410  periodically checks the positions of the various flag members  211 , and removes cassettes for which the associated flag member  211  is in the FINISHED position. The operator then resets the flag members for the empty carousel cassette positions to the NEW position and loads new cassettes in the carousel at these cassette positions. It will be appreciated that it is not necessary for step  410  to be performed in synchronization with, or at any particular time relative to, the other steps. 
     The cycle then returns to step  404 , where the carousel is indexed to the next cassette position, and the position of the associated flag member  211  is read. If the processing state indicating position of the flag member  211  for the next carousel position is other than NEW, then step  406  is not performed next. Instead, if the flag member is in the FINISHED position, step  412  is performed, wherein an alarm is set to alert the operator to replace the finished cassette, and the process returns to step  404 , resulting in the carousel being again indexed to the next cassette position and the position of the associated flag member  211  being read. If, during step  404 , the flag member is sensed to be in the STARTED position (which can result from a system malfunction, emergency shut-down or the like), then step  414  is performed. In step  414 , the wafer processing system is temporarily halted or suspended, and alarms are set notifying the operator that operator intervention is required. In response, the operator, in step  416 , removes the STARTED cassette(s) and sets the associated flag member(s) to the NEW position. The operator then commands the system controller to resume the wafer processing, which causes step  404  to be repeated. 
     It will be understood that the invention has been described with respect to specific embodiments thereof that are intended to be illustrative, not limiting, and that modifications may be made without departing from the spirit and scope of the invention.