Importance

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Abstract

Robot arm (16) end effectors (10, 110) of this invention rapidly and cleanly transfer between a wafer cassette (14) and a processing station semiconductor wafers (12) having diameters greater than 150 mm. The end effectors include proximal and distal rest pads (24, 26, 124,126) having pad and backstop portions (32, 34, 132, 134) that support and grip the wafer within an annular exclusion zone (30) that extends inward from a peripheral edge (30) of the wafer. An active contact point (50, 150) is movable by a vacuum actuated piston (52, 152) between a retracted wafer-loading position and an extended position that urges the wafer against the distal rest pads to grip the wafer within the exclusion zone. The end effector further includes fiber optic light transmission sensors (90, 102, 202) for locating the wafer periphery and bottom surface (100, 200). The sensors provide robot arm extension and elevation positioning data supporting methods of rapidly and accurately placing and retrieving a wafer from among a stack of closely spaced apart wafers stored in the wafer cassette. The methods effectively prevent accidental contact between the end effector and the wafers while effecting clean, but secure, gripping of the wafer at its edge or within its exclusion zone.

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First Claim