An optimal scheduling algorithm for the motion control of step and scan lithography

Step movement and scan movement are two main types of movement associated with step and scan optical lithography tools. To save moving time and ensure high accuracy of exposure scan, a novel time-optimal overlapping scheduling algorithm is proposed on the basis of serial scheduling algorithm. At first, the timetable on the switch time of each speed phase of separate successive step movement and scan movement is deduced according to S-curve acceleration and deceleration characteristics. Then the timetable is rescheduled by the proposed overlapping scheduling algorithm on the constraint of exposure scan so that the step movement and scan movement can be overlapped. As a result, the exposure efficiency of wafer is improved. The simulation and experimental results verify the correctness and validity of the proposed algorithm.