Design and tolerance analysis of compensator for high order aspheric surface testing

Abstract

High accuracy is required in surface testing of 90nm nodal point lithography projecting lens. By comparing various aspheric surface testing methods, we adopt Offner null compensator to test the aspheric surface in the point diffraction interferometer at last. In this paper, an Offner compensator is presented on the base of the third order aberration theory to test concave aspheric surface, the optical construction parameters of which is determined by introducing equal-quantities spherical aberration to compensate all orders of aspheric coefficients. The field of view of the system is 0.02o; the structure layout of the compensator is a meniscus positive lens combined with a Plano-convex positive lens. The design results indicate that: primary and high order aberrations are balanced well, MTF exceeds diffraction limit, root-mean-square (RMS) of wave front error <λ/167. The F-number of the system can achieve F/1.64. By the analysis of the process of aspheric surface testing with the designed system, a loosen distribution of the tolerance was presented based on the accuracy of measuring apparatus.