The present invention relates to semiconductor wafer handling robots and the like, and in particular to a pivot arm assembly therefor having an integrally formed bearing construction, as well as a method for making the pivot arm assembly.
Semiconductor wafers are typically made from silicon and are used in semiconductor chips and integrated circuit fabrication. Because of the fragile nature of the silicon-based material, and very small thickness of each slice, the wafers can easily be damaged through mishandling. Modern semiconductor processing systems must handle the wafers quickly and accurately in a very sterile environment to prevent contamination or damage to the processed semiconductor wafers and/or assembled chips.
Robots for handling semiconductor wafers and the like are generally well known in the art. Wafer handling robots, such as those disclosed in U.S. Pat. No. 6,817,640 and 2002/0182036 to Applied Materials, Inc., typically include at least one pair of wafer robot pivots or pivot arms which extend and retract a robot wrist or other similar articulated portion of the robot. As illustrated in FIG. 5A of U.S. Pat. No. 6,817,640 and FIG. 5 of Patent Publication 2002/0182036, each of the pivot arms typically includes an outwardly extending arm adapted for connection with a robot articulation member, as well as a gear segment with teeth which mesh with a robot drive mechanism.
As illustrated in FIG. 1 herein, heretofore, robot pivot arms have typically been fabricated from a plate of metal with a pair of circular recesses formed in opposite faces of one end of the plate in which two ball bearings are mounted. In the example shown in FIG. 1 of the present application, two angular contact ball bearings are mounted in the arm recesses in an angular contact, back-to-back relationship, with the contact angles oriented in opposite directions, so as to support thrust loads and/or clamping forces applied to either side of the bearing assembly. While the dual bearing configuration illustrated in FIG. 1 herein has served to maintain precise orientation, alignment and rotation of the pivot arm, certain drawbacks have been experienced. More specifically, it has been discovered that such bearing mounting arrangements experience infinitesimal small rubbing movement or fretting between the outer races of the bearings and the housing arm recesses, which results in the production of very fine metallic particles or debris that migrates throughout the robot machine thereby causing damage to the moving parts, as well as contaminating the wafers and/or semiconductor chips. In the event the two ball bearings shown in the prior design of FIG. 1 herein are inadvertently installed backwards or otherwise improperly, even more sever fretting results, which destroys the sterile environment in which semiconductor wafers must be handled.