Noncentering specimen prealigner having improved specimen edge detection and tracking

摘要

A prealigner (10) employs an X-Y stage (20) and a rotary stage (26) to position and orient a specimen (12) without centering it on the prealigner. In a preferred embodiment, the rotary stage is mounted on the X-Y stage and receives a semiconductor (12) in a substantially arbitrary position and orientation. The prealigner employs the rotary stage and translation in only an X-axis direction to scan the peripheral edge (76) of the wafer across an optical scanning assembly (36) to form a polar coordinate map of the wafer. A microprocessor (162) determines the location and orientation of the wafer from the map and cooperates with a motor drive controller (122) to generate control signals for positioning and orienting the wafer in the preselected alignment without changing the location at which the wafer is held.