Abstract:
An apparatus and method for simultaneously cycle-testing two wafer storage containers is provided. The two wafer containers are maintained in a counterbalance relationship to each other and cycled in a vertical up-and-down motion to simulate the forces of a selected overhead transport system.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to machinery used to test containers for wafer cassettes and, more particularly, relates to a hoist jig that repeatedly cycles two wafer containers, such as front opening unified pods, in order to simulate the vertical forces exerted by a selected overhead transport system. 
     2. Description of the Related Art 
     In the manufacturing process of semiconductor wafers, different-sized wafers require cassettes having different dimensions. Many current production lines use 150 mm and 200 mm diameter wafer; next generation lines will use 300 mm wafers. Therefore, next generation equipment has been designed to accommodate 300 mm wafers. One type of such equipment is wafer-storage cassettes. 
     Wafer transfer systems are used to provide an automated transfer of semiconductor wafers from one position to another position. For example, the wafers contained in a cassette may be moved individually to a processing chamber for depositing and patterning layers of material for forming integrated circuit chips. Robotic handling devices are preferred, since human handling is more likely to cause contamination. 
     The wafer-storage cassettes are often themselves stored and transferred in a pod. One type of wafer storage pod is referred to as a Standardized Mechanical InterFace (SMIF) pod. A SMIF pod is described in U.S. Pat. No. 5,653,565, which is assigned to Bonora et al. and is incorporated by reference herein in its entirety. The SMIF pod includes a cover that mates with a door to provide a sealed environment for the wafers within the cassette. When the wafers are to be transferred to a processing station, the pod is placed onto an access port of a transfer system such that the pod door is in contact with the access port. 
     Another type of wafer storage pod is sometimes referred to in the industry as a Front Opening Unified Pod (FOUP). A FOUP has an access door located on a side that is perpendicular to horizontally stored wafers and is used for 300 mm diameter semiconductor wafers. Automated transfer systems for use with FOUPs have been designed. FOUPs are designed to be lifted and lowered by automated material handling systems (AMHS), such as overhead hoist transport (OHT) systems. OHT systems result in mechanical wear of the FOUP due to repeated lifting and lowering. 
     SUMMARY OF THE INVENTION 
     A hoist jig comprises a vertically upright center member having a first surface and a second surface and a base coupled to the center member. The hoist jig further comprises a first support arm and a second support arm. The first support arm is coupled in a vertically slideable relationship to the first surface of the center member, the first support arm being configured to receive a first wafer storage container. The second support arm is coupled in a vertically slideable relationship to the second surface of the center member, the second support arm being configured to receive a second wafer storage container. The hoist jig further comprises a cycle mechanism that is operable to cycle the first wafer storage container and the second wafer storage container in a vertical up-and-down motion. The cycle mechanism is further operable to maintain the first wafer storage container and the second wafer storage container in a counterbalanced relationship with each other. 
     A method of testing two wafer containers simultaneously comprises coupling a first wafer container to a first support arm, wherein the first support arm is coupled to a first surface of a center member. The method further comprises coupling a second wafer container to a second support arm, wherein the second support arm is coupled to a second surface of a center member. The method further comprises maintaining the first wafer container and the second wafer container in a counterbalanced relationship with each other. The method further comprises cycling the first wafer container and the second wafer container in a vertical up-and-down motion at a speed that simulates the vertical forces exerted by a selected automated material handling system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings. 
     FIG. 1 is a plan view of a FOUP hoist jig. 
     FIG. 2 is a side view of a FOUP hoist jig. 
     FIG. 3A is an expanded side view of a pillow block and linear guides of a FOUP hoist jig. 
     FIG. 3B is an expanded side view of a pillow block and linear guides of a FOUP hoist jig. 
     FIG. 4 is an expanded front view of a pillow block, support arm, and linear guide of a FOUP hoist jig. 
     FIG. 5 is an expanded top view of limit switches on a FOUP hoist jig. 
     FIG. 6 is an interior view of a control box of a FOUP hoist jig. 
     FIG. 7 is an exterior view of a control box of a FOUP hoist jig. 
     FIGS. 8A and 8B illustrate a top view of a motor and chain assembly of a FOUP hoist jig. 
     FIG. 8C illustrates a side view of a motor and chain assembly of a FOUP hoist jig. 
     FIG. 9 is a schematic illustrating a motor control circuit for a FOUP hoist jig. 
     FIG. 10 is a diagram of a wafer adapter that may be employed within a 300 mm FOUP to retain 150 mm wafers. 
     FIG. 11A is a flow chart illustrating an initial phase of a method of performing cycle testing using a FOUP hoist jig. 
     FIG. 11B is a flow chart illustrating first and second cycle-direction phases of a method of performing cycle testing using a FOUP hoist jig. 
    
    
     DETAILED DESCRIPTION 
     The following sets forth a detailed description of a mode for carrying out the invention. The description is intended to be illustrative of the invention and should not be taken to be limiting. 
     In a test environment, mechanical wear on a FOUP can be observed to predict the life expectancy of the FOUP in a particular manufacturing environment. For example, mechanical wear on a FOUP that will be produced by a particular OHT system can be simulated in the testing environment. Such testing may include “cycle testing”—repeatedly lifting and lowering the FOUP to the height that the FOUP would be lifted to in the OHT system. 
     An OHT system, being an overhead system, lifts a FOUP from a first piece of fab machinery to a specific overhead height associated with the OHT system. The FOUP is transported via an overhead monorail-type transport system to a second piece of machinery. The OHT system then lowers the FOUP from the overhead transport system to the second piece of machinery. In order to simulate the mechanical forces applied to a FOUP by an OHT system, the hoist jig described herein simulates the height differential between fab machines and the OHT system, and further simulates the rate at which a particular OHT system lifts the FOUP. Prior art devices that lift the FOUP at an arbitrary rate that is not associated with a particular OHT system does not meet this objective. Similarly, a prior art device that lifts the FOUP to an arbitrary height not associated with the particular OHT system also fails to meet this objective. 
     Illustrated in FIGS. 1 and 2 is a FOUP hoist jig  100  that meets the objective of simulating the mechanical forces applied to a FOUP by a particular OHT system. In addition, other features of a FOUP&#39;s performance can be monitored in a test environment when it is cycle tested on the hoist jig  100 . For instance, by placing wafers inside the FOUP  110  and then lifting and lowering the FOUP  110 , resultant particles on the wafers can be monitored. In this manner, the sealing integrity of the FOUP  110  against a “bellows effect” can be tested. With information supplied during testing with the hoist jig  100 , the life expectancy and integrity of various FOUP models can be evaluated for a particular OHT system. Such evaluations can aid, for example, in a purchasing selection among a plurality of FOUP vendors. 
     FIGS. 1 and 2 illustrate a FOUP hoist jig  100  that is configured to simultaneously test two FOUPs  110   a,    110   b.  The lift/lower velocity curve of the hoist jig  100  is adjustable, allowing for simulation of acceleration and forces associated with various OHT systems. 
     The hoist jig&#39;s  100  ability to repeatedly lift and lower two FOUPs simultaneously provides distinct advantages over prior art systems that do not provide such dual-testing capability. One such advantage is that two FOUP units are subjected to exactly the same forces during testing, allowing for comparison of two FOUP units that have undergone exactly the same mechanical stresses. This advantage is particularly useful when comparing the performance of two FOUP units manufactured by different respective vendors. Another advantage of the dual-testing capability is the ability to test twice as many FOUP units in a given amount of time. The ability to test two FOUPs simultaneously therefore reduces the testing time required to test a given number of FOUPs. 
     FIGS. 1 and 2 illustrate that the hoist jig  100  includes a center member  108  and a base  102 . The base  102  includes two side members  106   a,    106   b  and two end members  104   a,    104   b.  The side members  106   a,    106   b  are configured in a parallel relationship with each other. The end members  104   a,    104   b  are also configured in a parallel relationship to each other. The side members  106   a,    106   b  are perpendicular to the end members  104   a,    104   b.  Parallel to the end members  104   a,    104   b  and perpendicular to the side members  106   a,    106   b  is a lower crossbar member  107  spaced equidistantly between the end members  104   a,    104   b.  One skilled in the art will recognize that the base  102  may instead be any structure, including and integrally formed one-piece base, that is configured to support the center member  108  in an upright position. 
     A first upright member  112   a  and a second upright member  112   b  form the outer edges of an upright frame  101  that is coupled to the base  102 . The lower cross-bar member  107  and an upper cross-bar member  114  are coupled to the upright members  112   a,    112   b  in order to form the rectangular-shaped frame  101 . Additional support members  120  are coupled between the base  102  and the frame  101  in order to provide additional support for the frame  101  and keep it in an upright (vertical) orientation. One skilled in the art will recognize that the main objective of the base  102  and frame  101  is to support the center member  108  in an upright vertical position so that it can perform cycle testing on FOUP units  110   a,    110   b  to simulate the forces applied to the FOUPs  110   a,    110   b  by an OHT system. As long as this objective is achieved, any manner of variations of the base  102  and the frame  101  are possible. For instance, the frame  101  need not necessarily be rectangular in shape. Furthermore, the frame  101  may be stabilized in an upright position by any means that provides for maintaining the frame  101  in an upright position—the additional support members  120  are merely one embodiment of such a stabilization means. 
     FIGS. 1,  2 ,  3 A,  3 B, and  4  illustrate that a pair of guide rails  206  are mounted to each of a first surface  109   a  and second surface  109   b  of the center member  108 . In a preferred embodiment, the guide rails  206  are cylindrical stainless steel members and are mounted to the center member  108  via traditional bolts. The hoist jig  100  also includes pillow blocks  202   a,    202   b  mounted in a slideable relationship with a pair of the guide rails  206   a,    206   b.  The pillow blocks  202   a,    202   b  are configured such that one FOUP  110  can be mounted to each pillow block  202 . In at least one embodiment, the guide rails  206  are linear to allow for smooth vertical linear motion of the pillow blocks  202   a,    202   b  as they move in a vertical path along the guide rails  206 . In this manner, the two FOUPs  110   a,    110   b  provide counterweight for each other. A preferred embodiment of the guide rails  206   a,    206   b,    206   c,    206   d  and pillow blocks  202   a,    202   b  are marketed as model 2DA-12-JOB L72 by Thomson Industries, Inc. in Port Washington, N.Y. 
     FIGS. 1 and 5 illustrate that a limit switch  208   a,    208   b  is mounted at or near the base of each guide rail  206  in order to physically prevent the pillow block  202  from sliding off the linear guide rail  206  in the case of malfunction or mis-operation. As used herein, the “base” of a guide rail  206  indicates a portion of the guide rail at or near the end of the guide rail  206  that is closest to the base  102  (the other end of the guide rail  206  being closer to the upper cross-bar member  114 ). When any limit switch  208  is activated, power to the motor  121  is removed. In a preferred embodiment, the limit switch  208  is a slim enclosed pre-wired limit switch, such as the D4C limit switch produced by OMRON Corporation with North American headquarters in Schaumburg, Ill. 
     FIGS. 1,  3 A,  3 B,  4  and  5  illustrate that a support arm  210  is coupled to each pillow block  202 . The point of coupling between the support arm  210  and the pillow block  202  may be fortified with supporting members  212 ,  214 . The support arm  210  is configured to form an aperture  310  into which a portion of a FOUP  110  may be slideably installed. The aperture  310  is sized and shaped to form a friction hold on the installed FOUP  110 . Furthermore, screws in the aperture are tightened to keep the FOUP  110  in place. 
     FIGS. 1 and 8, including FIGS. 8A,  8 B, and  8 C, illustrate that the hoist jig  100  includes a motor  121 . In at least one embodiment, the motor  121  is a stepper motor that requires pulses rather than DC current. In a preferred embodiment, the motor  121  is a five-phase stepping motor that allows for higher holding torque, has higher precision, and is easier to control than a standard AC or DC motor. In a preferred embodiment, the motor  121  comprises the PK596BUA stepper motor marketed by Oriental Motor U.S.A. Corporation in Torrance, Calif. The motor  121  includes a motor shaft  806  that rotates when the motor is in operation. The motor shaft  806  is coupled to a drive shaft  804  by a flexible motor coupling  808 . The motor coupling  808  couples the motor shaft  806  to the drive shaft  804  and operates to reduce backlash and compensate for misalignment between the two shafts  804 ,  806 . In a preferred embodiment, the motor coupling  808  is a flexible coupling bearing part number CO80S-9 and marketed by Berg, Inc. in Shreveport, La. 
     The motor  121  operates to drive a drive shaft  804  which, in turn, operates to ultimately raise and lower the FOUPs  110   a,    110   b.  This raise/lower action is facilitated through the operation of a sprocket wheel  812  and chain  204  mounted to the drive shaft  806 . Two shaft bearings  814   a,    814   b  further facilitate the raise/lower rotational movement. The mounted shaft bearings  814   a,    814   b  are mounted on the drive shaft  806  and allow the drive shaft  806  to rotate freely with little friction. In a preferred embodiment, the shaft bearings  814   a,    814   b  are stainless steel with low particulation, such as part number 6357K12 marketed by McMaster-Carr Supply Company in Chicago, Ill. A motor damper  810  mounted on the drive shaft  806  absorbs motor shaft vibration. In a preferred embodiment, the motor damper  810  is model number D9CL-12.7 marketed by Oriental Motor U.S.A. Corporation in Torrance, Calif. A motor mount  820  serves to secure the motor  121  to the upper cross-bar member  114 . 
     FIGS. 1,  6 ,  7 , and  9  are referred to for a discussion of control circuitry that supplies power and controls operation of the motor  121 . The motor  121  is driven, in at least one embodiment, by a motor driver  612 . A preferred embodiment of the motor driver  612  is marketed as part number UDK5114NA by Oriental Motor U.S.A. Corporation in Torrance, Calif. The motor driver receives pulses (“pulse −,” “pulse +”) from a motor controller  614 , which indicates the desired speed of operation of the motor  121 . The motor driver  612  also receives a direction signal (“CW/CCW −,” “CW/CCW +”) from the motor controller  614 . Using these inputs, the motor driver  612  drives the five phases of the stepping motor  121 . 
     The motor controller  614  allows the speed and acceleration with which the FOUPs  110   a,    110   b  under test are lifted and lowered to be adjusted. The variability of speed, direction, and torque of the motor  121  are user-controlled via a push-button interface  622  on the motor controller  614 . The motor controller  614  sends signals to the motor driver  612  in order to control the speed and direction of the motor  121 . The desired velocity profile (speed, acceleration, duration) of the up and down cycles to be performed by the hoist jig  100  are programmed by a user into the motor controller  614  via the push-button interface  622 . This variability in operation of the motor  121  provides that the hoist jig  100  is adjustable to simulate parameters, such as lift/lower velocity and acceleration, of various different OHT systems. 
     The control circuitry of the hoist jig  100  further includes a counter  616 . The counter  616  is used to track the number of cycles that have been performed by the hoist jig  100  during a particular test session. When the desired number of cycles has been performed, the counter  616  causes power to be removed from the motor  121  with the result that the hoist jig  100  ceases operation. A preferred embodiment of the counter  616  marketed as model H8CA-S by OMRON Corporation with North American headquarters in Schaumburg, Ill. 
     A DC power supply  618  provides DC power to those components of the control circuitry that require it, such as the motor controller  614 , motor driver  612 , and limit switches  208 . A preferred embodiment of the DC power supply  618  provides 7.5 W power and is marketed as model PS5R-A24 by Idec Corporation (USA) in Sunnyvale, Calif. 
     A time-delay relay  606  sends a signal at regular, adjustable intervals to the motor controller  614  to start each cycle. A preferred embodiment of the time-delay relay  606  is marketed as model TR-65122 by Macromatic Controls, LLC, in Milwaukee, Wis. 
     An emergency off (EMO) button  702 , when depressed, removes power to the motor  121 . A preferred embodiment of the EMO button  702  is marketed as model HA1B-V2ER by Idec Corporation (USA) in Sunnyvale, Calif. 
     FIGS. 7 and 8, including FIGS. 8A,  8 B, and  8 C, illustrate that the DC power supply  618  and control circuitry such as the motor controller  614 , counter  616 , motor driver  612 , and time-delay relay  606  as well as a circuit breaker  608  and terminal block  610 , are housed within a housing box  118 . The housing box  118  includes a front cover  602  and a housing body  604 . The housing box  118  may be mounted at any convenient location. In a preferred embodiment, the housing box is mounted to the frame  101  (FIG.  1 ). 
     Reference is made to FIGS. 1,  5 ,  8 A,  9 ,  11 A and  11 B in further discussing the operation of the hoist jig  100 . In an initial phase  1100  of operation, the FOUP units  110   a,    110   b  are moved to a home position wherein one FOUP  110  is at the top of its guide rails  206  and the other FOUP is positioned at the bottom of its guide rails  206 . To initiate this initial phase, a home position command  1102  is received by the motor  121  in operation  1104 . The user issues the home position command  1102  using the push-button interface  622 . Subsequent to receiving the home position command  1120 , the motor  121  begins to slowly rotate unless the home position sensor  902  has been triggered. If the home position sensor  902  has not been triggered, the motor  121  rotates slowly in operation  1108  until the home position sensor  902  is triggered. The slow rotation of the motor  121  causes the drive shaft  804  to rotate, causing the chain  204  to move vertically, which in turn causes the FOUP units  110   a,    1110   b  to move into home position. When the FOUP units  110   a,    110   b  reach home position, the home position sensor  902  is triggered. When motor  121  detects, in operation  1106 , that the home position sensor  902  has been triggered, the motor  121  stops rotating in operation  1110 . 
     FIG. 11B illustrates that, once the FOUP units  110   a,    110   b  have attained home position, they are ready for cycle testing. A cycle includes a first-direction cycle operation  1120 , a pause operation  1130 , and a second-direction operation  1140 . These operations  1120 ,  1130 , and  1140  are repeated for a predetermined number of cycles. During the first-direction cycle operation  1120 , the motor  121  rotatingly accelerates in operation  1122 . This accelerating rotation of the motor  121  rotates the drive shaft  804  and, accordingly, vertically moves the chain  204 . This movement causes the FOUP units  110   a,    110   b  to accelerate from their home position toward the opposite position (i.e., top FOUP moves down and bottom FOUP moves up). The acceleration in operation  1122  occurs at a rate of a 1  until the FOUP units  110   a,    110   b  reach a velocity of v. In operation  1124 , the velocity of the FOUP units  110   a,    110   b  is held constant at velocity v for a period of time t. After the period of time t has expired, the motor  121  decelerates in operation  1126  at a rate of a 2  until the motor  121 , (and, accordingly, the FOUP units  110   a,    110   b ) comes to a stop in operation  1128 . When the motor comes to a stop, the first-direction cycle operation  1120  has terminated. 
     After the first-direction cycle operation  1120  has terminated, a pause operation  1130  occurs. During the pause operation  1130 , a time delay relay  606  causes the motor  121  to pause for a predetermined span of time in operation  1132 . During that time, the clockwise/counterclockwise (CW/CCW+, CW/CCW−) input to the motor is toggled in operation  1134 . Accordingly, the rotational direction of the motor  121  during the second-direction cycle operation  1140  will be the opposite of the direction of the first-direction cycle operation  1120 . 
     During the second-direction cycle operation  1140 , the motor  121  accelerates (going in the opposite direction now) in operation  1142 , and, accordingly, the FOUP units  110   a,    110   b  move back toward their original home position at a rate of a 1  until the desired velocity of v is reached. In operation  1144 , the velocity is held constant at v for time t. In operation  1146 , the motor slows down at a rate of a 2 , causing the FOUP units  110   a,    110   b  to slow in turn, until the FOUP units  110   a,    110   b  come to a stop in operation  1148 . 
     In operation  1149 , the motor direction is reversed in case additional cycles are required. 
     If additional cycles are required, operation returns to the first-direction cycle operation  1120 . Otherwise, cycle testing is complete and the motor remains idle  1160 . 
     According to the foregoing method, FOUP units  110   a,    110   b  are cycle tested by the hoist jig  100 . Input values are set in order to emulate forces applied by a particular material handling system such as a selected OHT system. For instance, in a least one embodiment an OHT system is emulated by setting a 1  to a value of 2.0 meters/second 2 , setting v to a value of 1 meter/second, setting t to a value of 1 second, and setting a 2  to a value of −2.0 meters/second 2 . Of course, such values can be modified to emulate other material handling systems. The inventors have observed that, with the settings indicated herein, a full cycle takes approximately six seconds to complete. 
     FIG. 10 illustrates a wafer adapter  1000  that may be employed within a 300 mm FOUP  110  to retain 150 mm wafers. The wafer adapter  1000  is fashioned to retain a 150 mm wafer  1010  via holding pins  1012   a,    1012   b,    1210   c.  The wafer adapter  1000  is configured of a size and shape to be retained within a FOUP  110 . When 150 mm wafers are retained within a FOUP  110  via the wafer adapter  1000 , the sealing integrity of the FOUP  110  against a “bellows effect” can be performed on 150 mm wafers. This ability is useful, for instance, when the hoist jig is used to test the relative benefits of various FOUPs when a fab is considering moving from a 150 mm to a 300 mm wafer manufacturing scheme. In such case, exemplar FOUPs may be tested without the need to obtain relatively more expensive 300 mm wafers, as readily available 150 mm wafers may used with the aid of the wafer adapter  1000 . 
     ALTERNATIVE EMBODIMENTS 
     While particular embodiments of the present invention have been shown and described, it will be recognized to those skilled in the art that, based upon the teachings herein, further changes and modifications may be made without departing from this invention and its broader aspects and, thus, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of the invention. 
     For instance, the hoist jig  100  may be used with any wafer retainer device and need not necessarily be limited to FOUP units.