Abstract

An automatic wafer alignment station is disclosed for aligning a wafer having flats about its centroid with the flats oriented in a preselected spatial direction. The wafer is held by a vacuum chuck which is operatively connected to a motor driven carriage for controlled movement about an X axis, to a θ actuator carried by the carriage for controlled rotation about the axis of the chuck, and to a Z actuator carried by the carriage for controlled motion about a Z axis. An X capacitive sensor and a Z capacitive sensor are positioned near the wafer. An X processing and Z compensating circuit is responsive to the X and the Z capacitive sensor output signals and provides an electrical signal that has values which exclusively represent the position of the edge of the wafer along the X axis only over a predetermined angular range. Circuit means including an A/D converter and a microprocessor respond to the electrical signal and produce a plurality of corrective signals to the X, Y, and θ actuators for aligning the wafer about its centroid and for orienting the flats of the wafer in a preselected spatial orientation.