Workpiece transfer device

A workpiece transfer assembly for manipulating one or more workpieces, such as semiconductor wafers includes a plurality of coacting arms that include one or more arcuate portions corresponding to an outer diameter of a workpiece. The arcuate portion has a workpiece engaging surface adapted to engage an outer edge of the workpiece. At least one of the coacting arms includes a flexure assembly that allows deformation of the workpiece engaging surface in a direction away from the workpiece in response to pressure on the outer edge of the workpiece from the workpiece engaging surface.

TECHNICAL FIELD

The present invention relates generally to ion implantation equipment and more particularly to an improved end station for an ion implantation.

BACKGROUND

The processing of semiconductor wafers involves many processing steps including implantation, thermal processing, and selective exposure to various chemical agents. As wafers proceed through an implantation facility they are transferred between specialized processing chambers and stations. Robots are routinely used to transfer wafers. The robots have specialized end effectors adapted to securely grip semiconductor wafers. During processing semiconductor wafers are susceptible to defects caused by non-uniform or excessive forces, particularly around the edges of the wafer, and damage done by end effectors can adversely affect the yield of semiconductor wafers.

SUMMARY

Including a flexure as part of a workpiece transfer arm regulates the amount of pressure that is placed on the workpiece edge and reduces the likelihood of pressure induced defects such as particle generation.

A workpiece transfer assembly for manipulating one or more workpieces, such as semiconductor wafers, includes a plurality of coacting arms that include one or more workpiece engaging portions corresponding to an outer contour of a workpiece. The workpiece engaging portion has a workpiece engaging surface adapted to engage an edge of the outer contour of the workpiece. At least one of the coacting arms includes a flexure assembly that allows deformation of the workpiece engaging surface in a direction away from the workpiece edge in response to pressure on the outer edge of the workpiece from the workpiece engaging surface.

The workpiece transfer assembly may advantageously include a pair of coacting arms including a fixed arm and a moving arm that rotates about a pivot point to engage the outer edge of the workpiece. In this instance, each of the coacting arms includes an arcuate portion at each of two distal ends. Each coacting arm is connected to the pivot point. Either arm may include a flexure assembly that forms a part of the arm outside of the workpiece engaging surface such as a notch cut into the arm between a pivot portion of the arm and a workpiece engaging portion of the arm. The flexure assembly may also be a flexible finger that forms the workpiece engaging surface.

DESCRIPTION

FIG. 1illustrates a workpiece handling robot10adapted for use with semiconductor wafers. The robot includes a robot body11from which a rotatable shaft12protrudes. At a distal end of the shaft12a transfer arm assembly, designated generally at reference character14, is mounted for transferring workpieces between processing and storage stations. The transfer arm assembly14includes a pair of workpiece support arms. A fixed arm15is fixed to the rotating shaft12and does not move relative to the shaft. A moving arm19is capable of relative motion with respect to the rotating shaft12. The relative motion of the moving arm is limited as shown inFIG. 2to a short excursion “L” as the moving arm is rotated about a pivot mounting point20between a retention position shown inFIG. 1and a release position shown inFIGS. 5A and 5D.

As also shown inFIG. 2, the robot body is connected to a linear actuator33that moves the transfer arm assembly10along a linear path designated “N” inFIG. 2. A rotation drive unit31is coupled to the shaft12and includes a first rotation drive unit35that rotates the shaft12and the entire arm assembly14in the orientation shown as “M.” A second rotation drive unit34drives a secondary shaft that is inside and coaxial with the shaft12. The secondary shaft also rotates in the M orientation and moves the moving arm relative to the fixed arm in the excursion L that corresponds to a few degrees of rotation.

The transfer arm assembly14includes at least one flexure component that provides stress relief when the moving arm19is rotated such that a workpiece is supported along portions of its edge by the arms. While the transfer arm assembly shown inFIG. 1includes several flexure components on each arm, the flexure components could be present only on one of the arms, advantageously the moving arm. The characteristics of the flexure are chosen to provide a given amount of displacement in response to an expected force exerted on the moving arm by the workpiece edge when the moving arm is moved into its workpiece retention position. In this manner, the transfer arm or arms yield to relieve stress on the workpiece edge. An arm flexure41shown inFIGS. 1 and 3and comprises a notch cut into the arm19between arm portions19aand19b.

Multiple workpiece engaging flexures25are shown disposed on both the fixed arm15and moving arm19.FIG. 4shows a cross section of a workpiece engaging flexure. A flexing workpiece support finger26, that can be advantageously made from Vespel or PEEK material, extends perpendicular to a mounting body portion29that is connected the moving arm19. The workpiece support finger26is cantilevered from the body portion29and flexes in the direction designated “K” in response to force exerted by the edge of the workpiece13. The flexibility of the finger26in increased by a notch26athat is present between the body portion29and the finger26. The workpiece edge is supported by a generally V shaped channel27in the finger26. In this manner, when the moving arm is moved to the retention position, the workpiece support finger26is able to yield to reduce stress on the edge of the workpiece.

FIGS. 5A-5Dillustrate a sequence of positions taken by the transfer arm assembly14during normal operation in which the positions of two workpieces A, B are swapped. InFIG. 5Athe transfer arm assembly is in a park position. The moving arm19is in its release position, spaced apart from the fixed arm15by a distance “X” that is slightly larger than the diameter of a workpiece A, B. As shown inFIG. 5Bthe transfer arm assembly is rotated 90 degrees into proximity with the workpieces and the moving arm19is moved toward the fixed arm15to its retention position. The flexure assemblies on the moving arm flex to relieve stress on the workpiece edge. Moving from5B to5C, the transfer arm assembly14is then rotated 180 degrees and the positions of the workpieces is swapped. The moving arm is then moved to its release position and the transfer arm assembly then rotates 90 degrees back to its park position as shown inFIG. 5D. Linear motion (not shown) along N (FIG. 2) is used to remove workpieces from an electrostatic chuck and a load-lock.

While the invention has been described with a degree of particularity, it is the intent that the invention includes all modifications and alterations from the disclosed design falling within the spirit or scope of the appended claims.