Abstract:
Disclosed are apparatus and methods used for handling semiconductor wafers or similar articles. In particular, the apparatus disclosed is capable of flexibly gripping items of various shapes and sizes in a manner that substantially reduces or eliminates the likelihood of damage thereto. The apparatus is particularly suited to being used as a robotic end effector for handling wafers using edge-gripping techniques.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application incorporates by reference, and claims priority to and the benefit of, U.S. Provisional Patent Application serial No. 60/237,251, which was filed on Oct. 2, 2000. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to apparatus and methods for handling semiconductor wafers or similar articles. More particularly, the present invention relates to a robotic end effector for handling semiconductor wafers using edge-gripping techniques. 
     BACKGROUND INFORMATION 
     Semiconductor manufacturing requires an ultra-clean environment for the silicon wafers during the manufacturing process; therefore it is highly desirable to have few moving parts in the wafer processing environment due to the risk of wear particles and the like migrating to the wafer surface, thereby contaminating the wafer and resulting in reduced production yields. Currently, the handling of semiconductor wafers and similar articles is accomplished using complex mechanical systems that require many moving parts. 
     Various examples of devices for handling wafers can be found in U.S. Pat. Nos. 4,449,885, 4,553,069, 4,681,213, 4,752,180, 4,773,687, 5,011,594, 5,046,909, 5,054,834, 5,547,515, 5,555,634, 5,692,873, 5,647,626, 5,765,890, 6,077,026, 6,086,976, 6,112,735, 6,116,848, 6,120,360, and 6,283,701, the disclosures of which are hereby incorporated herein by reference in their entirety. These devices hold wafers by various methods including mechanical clamping, vacuum pressure, electrostatic attraction, adhesives, chucks, and carrying trays. 
     Several drawbacks with current wafer holding techniques exist. For example, multiple moving parts have inherent reliability problems and are prone to failure. Additionally, vacuum pressure, clamping, and electrostatic devices typically require complex operating systems. Also, vacuum pressure, clamping and adhesives can damage wafer surfaces. 
     Certain devices exist for flexibly gripping items of various shapes; however, most are not suitable for handling semiconductor wafers. Examples of such devices can be found in U.S. Pat. Nos. 4,540,034, 4,839,947, and 5,121,908, the disclosures of which are hereby incorporated herein by reference in their entirety. 
     SUMMARY OF THE INVENTION 
     The invention relates to an apparatus for handling semiconductor wafers wherein the apparatus has a minimal number of moving parts. The invention is particularly useful in the handling of semiconductor wafers of varying diameters. Further, the apparatus handles wafers in a manner that substantially reduces or eliminates the likelihood of wafer damage. In addition, the apparatus can handle wafers by gripping the edges of the wafers, thereby eliminating the need for a carrier. 
     In one aspect, the invention includes a robotic end effector that includes at least one arm, a flexure joint, and a force element. In various embodiments, the force element can be an electric solenoid device, a pneumatic actuator, a piezoelectric actuator, or similar devices as known to those skilled in the art. In other embodiments, the end effector includes a second arm. One or both arms can be arcuate. The arms can be approximately the same length and the arms can include fingers for contacting the edges of a wafer. Furthermore, the apparatus need not be mounted on a robotic arm. 
     In another aspect, the invention relates to methods of handling wafers. One method includes the steps of moving an end effector into contact with a wafer, applying a force to the end effector, and removing the force on the end effector. Applying a force to the end effector causes at least one arm of the end effector to open by rotating away from the wafer. Once the end effector has fully grasped the wafer, the opening force is effectively removed. In one embodiment, the method includes the step of actuating a force element to open the flexure joint and release the wafer. 
     These and other objects, along with advantages and features of the present invention herein disclosed, will become apparent through reference to the following description, the accompanying drawings, and the claims. For example, the invention is scaleable and practical for use in handling materials other than semiconductor wafers. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which: 
     FIG. 1A is a schematic representation of one embodiment of an apparatus in accordance with the invention; 
     FIG. 1B is a schematic left side view of the apparatus of FIG. 1A; 
     FIGS. 2A-2C are schematic representations of the apparatus of FIG. 1A in various operating positions; 
     FIG. 3 is a schematic representation of an alternative embodiment of an apparatus in accordance with the invention; and 
     FIG. 4 is a schematic representation of another alternative embodiment of an apparatus in accordance with the invention. 
    
    
     DESCRIPTION 
     Embodiments of the present invention are described below. It is, however, expressly noted that the present invention is not limited to these embodiments, but rather the intention is that all equivalents and all modifications that are apparent to a person skilled in the art are also included. In particular, the present invention is not intended to be limited to apparatus for handling semiconductor wafers. 
     One embodiment of the present invention is illustrated in FIGS. 1A and 1B. The apparatus  2  includes an end effector or gripping element  4 , a flexure joint  8 , and a force element  10 . The end effector  4  includes two arms  5 A,  5 B that contact a wafer  12  about its peripheral edge  19 . The contact area  17  could be continuous, but it is generally preferable to limit the contact area to three contact points  17 A,  17 B,  17 C. The arms  5 A,  5 B can optionally include fingers  6 A,  6 B,  6 C for contacting the wafer&#39;s peripheral edge  19 . 
     The fingers  6 A,  6 B,  6 C are preferably formed of a hard, wear-resistant material to minimize friction between the fingers  6 A,  6 B,  6 C and the wafer  12 , thereby reducing particle generation. Although, depending on the specific application, the fingers  6 A,  6 B,  6 C can be any non-reactive material compatible with the item to be handled and suitable for use in various processing environments, for example, ceramic, rubber, or other dimensionally stable materials. In addition, the fingers  6 A,  6 B,  6 C may include a flexible component to absorb shock from the force of the arms  5 A,  5 B as they grip the wafer  12 . Typically, the fingers  6 A,  6 B,  6 C are solid pieces rigidly coupled to the arms  5 A,  5 B; however, the fingers  6 A,  6 B,  6 C could be rollers movably secured to the arms  5 A,  5 B. 
     The arms  5 A,  5 B are generally arcuate in shape, with the second arm  5 B oriented to oppose the first arm  5 A. The end effector  4  can be a single molded piece that includes the two arms  5 A,  5 B, a base  14 , and the flexure joint  8 . The end effector  2  can be manufactured out of natural or synthetic rubber or a resilient polymer resin so as to be compliant. Furthermore, the apparatus  2  can be mounted to a robotic arm  3 . Mounting can be done through any means known to those of skill in the art, for example by chemical bonding or mechanical means. The apparatus  2  shown in FIGS. 1A and 1B includes mounting hardware  16 A,  16 B on the base  14  for interfacing with the robotic arm  3 . 
     The flexure joint  8  acts as a hinge to allow the arms  5 A,  5 B to rotate away from a longitudinal axis  7  that bisects the wafer  12  once grasped. Essentially, the arms  5 A,  5 B open and close by means of a flexure. In the embodiment shown in FIGS. 1A and 1B, the flexure joint  8  is incorporated into the end effector  4 . Essentially, the flexure joint  8  is created by removing sufficient material from the intersections of the arms  5 A,  5 B with the base  14  to permit the arms  5 A,  5 B to pivot and rotate away from the longitudinal axis  7  in response to a predetermined force applied to the arms  5 A,  5 B. 
     The force element  10  shown in FIGS. 1A and 1B is coupled to arms  5 A,  5 B at points  11 A,  11 B. The force element  10  can be coupled by a variety of methods, such as bonding or threaded fasteners. Optionally, the force element  10  is rotatably or pivotally coupled at point  11 A or  11 B or both. Typical useful force elements include an electric solenoid, a pneumatic actuator, and an piezoelectric actuator. The force element  10  is used to release the wafer  12  by opening the arms  5 A,  5 B. For example, actuating the force element  10  applies an outward force on the arms  5 A,  5 B, thereby opening the flexure joint  8  and releasing the wafer  12 . 
     More specifically, FIGS. 2A-2C depict the operation of the apparatus  2  at three different stages. As shown in FIG. 2A, the apparatus  2  is moved towards the wafer  12  such that the end effector  4  contacts the wafer&#39;s peripheral edge  19 . The apparatus can be moved by a robotic arm or manually. Movement of the apparatus  2  continues in the direction of the wafer  12  such that a contact force is applied to the arms  5 A,  5 B. In response thereto, the arms  5 A,  5 B rotate outwardly from each other at the flexure joint  8 . 
     FIG. 2B depicts the apparatus  2  in an intermediate stage. As can be seen, the arms  5 A,  5 B have opened up to accept the wafer  12 . Force continues to be applied to the arms  5 A,  5 B until the arms  5 A,  5 B fully envelop and grasp the wafer  12 . At this point, all the fingers  6 A,  6 B,  6 C are in contact with the peripheral edge  19  of the wafer  12 , as shown in FIG.  2 C. As can be seen, the wafer  12  is securely gripped by the apparatus. The force element  10  is used to release the wafer  12 . The force element  10  forces open the arms  5 A,  5 B, thereby releasing the wafer  12 . 
     FIG. 3 depicts an alternative embodiment of the apparatus shown in FIG.  1 . The apparatus  20  is another one-piece construction apparatus  20  including an end effector  24  with arms  25 A,  25 B of equal length. Each arm  25 A,  25 B includes two fingers  26 A,  26 B,  26 C,  26 D for contacting the wafer  22 . The arms  25 A,  25 B flex in response to an applied contact force. The arms  25 A,  25 B rotate outwardly from longitudinal axis  27  and about the flexure joint  28 . 
     In the embodiment of the apparatus  32  shown in FIG. 4, the end effector  34  has a single, arcuate arm  35 . The angular sweep of the arm  35  can range from about 180 degrees to about 330 degrees, preferably about 210 degrees to 300 degrees, and more preferably about 240 degrees to about 270 degrees. The arm  35  includes three fingers  36 A,  36 B,  36 C, which are preferably, approximately equally space about the arm  35 . The apparatus  32  optionally includes a stop  39  that assists in the alignment of the wafer  42 . The optional stop  39  may include a finger  36 D for contacting the wafer  42 . 
     The material, thickness, and geometry of an end effector in accordance with the invention is selected to provide sufficient compliancy to the apparatus, such that the contact force required to open the arm(s) to receive the wafer is not excessive and the resulting clamping force when the wafer is captured and seated is sufficient to prevent the wafer from being dropped as it is accelerated and decelerated during transport in the wafer processing apparatus. 
     Having described certain embodiments of the invention, it will be apparent to those of ordinary skill in the art that other embodiments incorporating the concepts disclosed herein can be used without departing from the spirit and the scope of the invention. For example, the end effector need not be manufactured as a single piece, but could be two or more pieces bonded together or mechanically assembled. Accordingly, the described embodiments are to be considered in all respects only as illustrative and not restrictive. Therefore, it is intended that the scope of the present invention be only limited by the following claims.