This work presents a novel method to simultaneously measure a quarter-wave plate's phase retardation and fast axis using radially polarized vector beams and spatial Fourier analysis. The light beam is converted into a radially polarized beam after passing through a polarizer and a vortex retarder. The tested quarter-wave plate and a polarizer are placed after the vortex retarder in sequence, and an hourglass intensity distribution image is recorded by a camera. Then the phase retardation and fast axis of a quarter-wave plate can be calculated by using Fourier analysis of the recorded intensity image with a snapshot. The theoretical model of the proposed method is built based on the Stokes-Mueller formalism. And both simulation calculation and experiments are carried out with different fast axis angles of a quarter-wave plate. The measurement errors of the phase retardation and fast axis are also analyzed to validate the proposed method. Both simulation calculation and experimental results show good agreement with the theoretical values. It is demonstrated that the proposed method is convenient, simple, and accurate to measure the phase retardation and fast axis of a quarter-wave plate.
Resolution is one of the key performances of the lithography tool. Decreasing the exposure wavelength and increasing the numerical aperture (NA) of the objective lens can enhance the lithography tool resolution. Therefore, the exposure wavelength is reduced to deep ultraviolet (DUV), and a polarized illumination is adopted. The polarization effect of the exposure system seriously affects the imaging quality. The polarization parameters must be measured accurately. Due to the grating polarizer's compactness and wide acceptance angle, it is introduced to the polarization measurement. It could simplify the measurement system and achieve high-accuracy real-time measurement. A bilayer metallic grating polarizer with tapered slits is designed based on the inverse polarizing effect and transmission enhancement effect of TE-polarized light. The physical mechanism of transmission enhancement on TE-polarized light and transmission suppression on TM polarized light have been analyzed. The simulation results show that the enhancement of TE-polarized light transmission and the extinction ratio is mainly modulated by the middle dielectric layer height and the metal width and height of the top layer grating. For the designed grating polarizer with tapered slits, the transmission of TE-polarized light is 59.4%, and the extinction ratio is 75dB at normal incidence. Compared with the previous bilayer metal grating polarizer, both the TE transmission and extinction ratio are enhanced simultaneously. The designed grating polarizer can meet the performance requirements of the polarization measurement device in immersion lithography tools within a large process tolerance range.
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