Design of freeform illumination sources with arbitrary polarization for immersion lithography

Abstract

Polarized illumination and source mask optimization (SMO) are two prominent resolution enhancement technologies (RETs) in immersion lithography. Recently, source-mask-polarization optimization (SMPO) has been developed to support photolithographic process shrinks, which shows that the illumination system with arbitrary intensity and polarization distribution of light in the pupil is emergency. In this paper, we propose a unique illumination system design to match the target SMPO source and meet the requirement of immersion lithography at 45-16 nm node. In our designed illumination system, the adjustable λ/2 wave plates and mirror array are introduced to produce arbitrary intensity and polarization distribution of light in the pupil. The three λ/2 wave plates are designed to that can move freely in certain planes perpendicular to the optical path. To produce target SMPO sources, the positions of thousands spots reflected by adjustable mirrors array are firstly designed and optimized to approximate the target intensity distribution in the pupil corresponding to unpolarized light. Then the target polarization states in all the spots are obtained in the pupil by designing and optimizing the relative positions of the three wave plates. Compared with prior design method, our design results show that the intensity distribution and polarization state of all spots in the pupil match the target SMPO source accurately and efficiently with lower intensity lost.