Automatic design of an extreme ultraviolet lithography objective system based on the Seidel aberration theory

Abstract

In this paper, a method is proposed to solve the initial optical structure of an off-axis multimirror system for an extreme ultraviolet lithography (EUVL) application. By tracing the characteristic rays, the primary aberration can be expressed as a function of the distance and curvature based on the Seidel aberration theory. The initial structure with a favorable aberration performance is calculated when the function value is 0. We solve two different initial structures with an off-axis, six-mirror configuration with different optical powers. The NA of the finally optimized optical system is 0.25, the wavefront aberration rms value is less than 0.04 λ , and the absolute distortion is below 1.2 nm.