Method for compensation selection ofmicrolithographic optical system

Computer-aided alignment is very important for the correction of aberrations due to construction imperfections of microlithographic optical systems. The compensation results mostly depend on the selection of compensators. In this paper, an effective method for compensation selection considering optomechanical constraints is presented. The techniques are based on the linearity of compensators and treat compensator selection as a combinatorial optimization problem with the objective of minimum residual aberrations and compensator adjustment ranges. The method is reliable and offers a better combination of compensators under constraints of optomechanical structure. As an example, the method was applied to a lithographic lens with a numerical aperture (NA) of 0.75. The results show that compensators with minimum objective function value would get minimum residual aberrations and adjustment ranges compared to those with larger objective function values. This method presented in this paper could be a good solution for compensation selection in lithographic lenses and other similar optical systems.