Design and analysis of bilayer metallic grating polarizer with tapered slits in deep ultraviolet band

Abstract

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.