The study on photo mask pre-alignment approach based on Four-Quadrant-Photo-Detectors

In this note, an analysis was made on the characteristics of voltage signals from Four-Quadrant-Photo-Detectors (FQPDs) used in photo mask pre-alignment. With this, an algorithm was proposed to compute the photo mask´s pose offset with respect to FQPDs. In addition, a kinematic model was established for the manipulator´s movement in pre-alignment. Based on the pose offset calculating algorithm and the kinematic model, a pre-alignment approach was proposed. The validity of the presented pre-alignment approach was illustrated by the performance indexes of time cost in pre-alignments, and repeatiblity of photo masks, which are obtained from experiments.