Robot arm end effectors rapidly transfer semiconductor wafers between a wafer
cassette and a processing station. Preferred embodiments of the end effectors include
proximal and distal rest pads, the latter having pad and backstop portions that
support and grip the wafer at its peripheral edge or within an annular exclusion
zone that extends inward from the peripheral edge of the wafer. Preferred embodiments
of the end effectors also include fiber optic light transmission sensors for determining
various wafer surface, edge, thickness, tilt, and location parameters. 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 wafers stored in the wafer cassette.
