A five degree-of-freedom laser measurement model on wafer stage of scanning lithography

The principle of laser interferometry system applying on wafer stage position measurement is analyzed, Considering the characteristic of the interferometry system, the errors deteriorating the measurement precision are studied, which includes Abel error and cosine error, the influence of laser wave length, error originating from delay time and mirror unflatness et al. A five degree-of-freedom measurement model is presented which converts raw interference fringes to wafer stage coordinate position accurately, and the corresponding algorithm is designed to compensate the errors which deteriorate the measurement precision, which set the stage for realization of ultra-precision motion control of wafer stage. The measurement model depicted in this paper has been applied in scanning lithography successfully.