Data processing: generic control systems or specific application – Specific application – apparatus or process – Robot control
Reexamination Certificate
1999-06-23
2001-10-02
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Robot control
C700S246000, C340S565000, C340S870030, C340S870030, C340S870030, C340S870030, C901S001000, C477S906000, C477S907000, C074S490010
Reexamination Certificate
active
06298282
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a system for detecting faulty operation of a robot used in fabrication in general and particularly with reference to the fabrication of semiconductor devices, magnetic discs, optical discs and photomasks.
2. Brief Description of the Prior Art
This disclosure relates, in general, to a system for handling product with a robot arm and detecting scratching, rubbing or excessive vibration. While all descriptions herein relate to a semiconductor wafer, it should be understood that the invention has much greater application, such as, for example, in the fabrication of magnetic discs, optical discs and photomasks.
In the fabrication of semiconductor devices, it is necessary to transport semiconductor wafers in and out of cassettes as a part of the fabrication process. This transport is generally performed by the use of robotic arms wherein the arm grasps a semiconductor wafer and moves the wafer from a first location to a second location and, more specifically, in the transport of wafers into and out from a cassette. It is necessary that the path of transport of the wafer during such transport be accurately traveled and that the wafer be accurately oriented during such transport. Otherwise, in the event of, for example, robot misalignment, there is the possibility of the wafer traveling sufficiently out of its assigned path that it bumps into the carrier or scrapes against the cassette or other structure to cause an abrasion on the wafer, a microfracture or even shattering the wafer. This problem leads to diminution in yield and the requirement to stop the fabrication process in order to provide a clean-up of the equipment due to dust from abrasion or wafer particles from abrasion or shattering. Furthermore, the above described problem is only located in the prior art by a visual inspection, this meaning that equipment can run for long periods and produce faulty chips before the problem is noted and the faulty piece of equipment is fixed or replaced. Even when the faulty condition is noted, the system must be completely checked out to locate the faulty equipment. This is difficult in cases where the fault does not occur for every wafer position in the cassette, but only for a few wafer positions, since a service technician may not check every wafer position.
A prior art Kensington wafer sorter system has a robot arm to unload wafers and two light sensors to scan the dimensions and locations of the receiving positions in the cassette before the arm enters the cassette to grasp a wafer. If the cassette is warped or out-of-tolerance, then the out-of-tolerance condition will be detected, and the robot will be prevented from moving. This system, however, does not report the specific position which is out-of-tolerance.
SUMMARY OF THE INVENTION
In accordance with the present invention, the above described problem inherent in prior art fabrication processes using robotic arms is minimized, and there is provided a sensor located at each robotic arm of the system that grasps a wafer whereby some type of history and/or alarm and/or shut off of the fabrication process itself can be provided automatically when a faulty condition occurs, such as, for example, robot arm misalignment, with the location of the faulty condition being immediately noted and reported. The present invention adds to or replaces the prior art by providing the concept of checking of robot vibration during transport of every wafer. The wafer position having a problem is identified whereas the prior art Kensington sorter does not indicate which position has a problem, but only that there is some problem somewhere in the cassette.
Briefly, there is provided one or more of a vibration sensor on the robot arm and/or a vibration sensor on the wafer cassette itself and/or a particle sensor beneath and immediately adjacent the entrance to the wafer cassette to note the extent of particle fall during entry and removal of wafers into and out from the wafer cassette. The sensing equipment can be active continually or only during entry and removal (load/unload) of wafers from the wafer cassette by the robot arm or during motion of the robot arm and wafer through areas of potential jeopardy. In the event of a predetermined abnormal vibration of particle level, operation of the robot arm can be disabled. This operation could take into account the possibility of false alarms and required more than one abnormal event to provide shutdown. Abnormal vibration and/or increased particle count when the robot moves near the cassette indicates scratching jeopardy, can initiate equipment shutdown and provide an alarm. This provides a prewarning of impending robot handling errors and possible wafer damage or scrappage as a result thereof with the warning and possible production stoppage being provided at the first sign of trouble.
Advantages of the system as proposed in accordance with the present invention are ease of implementation, economy in the method of preventing scrap and particle generation, limitation of the error condition to as little as a single wafer and preventing the requirement for lengthy period for yield loss detection by engineering personnel. The system can be in operation of a full time basis or only during periods wherein the robot arm is in operation or only during that part of the robot arm operation during which wafers are grasped and held by the robot arm or when the robot and wafers are passed through regions with potential rubbing jeopardy.
In operation, the normal vibration and particle count are determined to provide a window of normal operation to minimize the likelihood of acting in response to a single or predetermined small number of false readings. A vibration sensor is placed on the robot arm and/or a particle monitor is placed beneath the entry to a cassette or cassette for holding wafers. It is understood that the normal air flow is from ceiling to floor, this causing the air flow passing along the entry to the cassette to be from the top of the cassette to the particle counter at the base of the cassette. A vibration sensor can also be placed beneath the cassette with the cassette resting thereon to sense vibration of the cassette itself The alarm system can be on continually, only when the robot arm is in operation or only when the robot arm is in operation and grasping and holding a wafer. It is preferred that the alarm system be operational only during actual grasping and holding of the wafer to minimize the possibility of a false alarm during robot arm periods of inactivity. The robot arm will then be operated periodically in its normal manner, grasping wafers, placing them into the proper slot in the cassette or grasping wafers in the cassette that have been operated upon and placing these wafers in another location. If, during operation of the robot arm there is sufficient misalignment of the wafer for whatever reason which causes scraping of the wafer by the cassette, the vibration sensor beneath the cassette and/or the vibration sensor on the robot are will note this fact due to vibration of the robot arm and/or the cassette. In addition, if there is scraping of the wafers by the cassette, the particles scraped from the wafer will follow the air steam of the ambient and pass through the particle monitor. The system can be tuned to any one or more of these detectors and provide a record, an alarm and/or shut down the system, based upon some predetermined error criteria or trigger level. When plural ones of the sensors are used concurrently, the indications from these sensors can be used to provide more accurate initial information or for the purpose of redundancy to minimize the likelihood of a false alarm. As an alternative, in the event an error condition is detected and it is determined that the error is due to the vertical positioning of the robot arm, the vertical position of the robot arm can be altered on line until the alarm condition is remedied.
While the invention herein is discussed with respect to vibration senso
Guldi Richard L.
Melcher Keith W.
Worley Robin D.
Brady III Wade James
Cuchlinski Jr. William A.
Marc McDieunel
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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