A method of polarization-mode conversion based on birefringent film in immersion lithographic illumination system

In immersion lithographic illumination system, appropriate polarization illumination can improve the resolution and imaging quality. Thus it is of great significance to realize different polarization-modes. The zero-order half-wave plates are usually used to achieve conversion of different polarization-modes. However, large-diameter zero-order half-wave plate is too thin to manufacture and assembling. This paper presents a polarization-modes conversion method based on birefringent film. The properties of birefringence film is similar to zero-order half-wave plate, and the film is easy to manufacture. Theoretically, it can be estimated that the film thickness is 2.4μm correspond to 180° retardation in 193nm wavelength. The experiment indicates that the 180° birefringent film can convert linear polarization-modes successfully, which verifies the feasibility of the film as a substitute of zero-order half-wave plate in immersion lithographic illumination system. The method solves the problem that it is difficult to manufacture large-diameter zero-order half-wave plates, and provide a reference for the design of lithographic illumination system.