A dual wafer prealigner and a multiple level structure

The purpose of this study is to examine the means by which multiple wafers may be aligned in order to reduce wafer handling time in wafer processes. We designed a multilevel structure for a prealigner which can simultaneously handle multiple wafers within a system. The system consists of gripping parts, kinematic parts, vacuum chucks, pneumatic units, hall sensors and a DSP controller. The procedure through which the wafers were aligned consists of two steps: mechanical gripping and notch finding. The first step comprises aligning a wafer along the XY direction using 4-point mechanical contact. The rotational error can be found by detecting a signal in the notch using hall sensors. A dual prealigner was designed for 300mm wafers and constructed for a performance test. The accuracy was monitored by checking the movement of a notch in a machine vision which is separated from the prealigner. The result indicates that the dual prealigner exhibits sufficient performance comparable to existing commercial products.