Cross-coupling control for synchronized scan of experimental wafer and reticle stage

In the step & scan lithography system, the wafer stage and reticle stage should scan simultaneously at a high speed and the speed ratio is 1:4. The synchronization between the two stages has significant effect on the quality of exposure. The wafer stage is four times heavier than the wafer stage and the response speeds are different, which adds difficulty to the synchronization control system. After the construction of each stage motion control system, two kinds of synchronization control methods are applied. The first one is parallel mode, where both of the stages track on the command as accurate as possible. The second one is cross-coupling control, where one of the stages can get the information on the other one and compensate the following error. Because the response speed of reticle stage is faster than that of the wafer stage, the wafer stage’s following error is feedback to the reticle stage’s controller. Two kinds of synchronization methods are compared. Experiment shows that the cross-coupling controller can much increase the synchronization performance of the two stages.