Surface plasmon mediated inverse polarization transmission through metallic gratings in deep ultraviolet band

Using conventional wire grid polarizers to manipulate the polarization of deep ultraviolet (DUV) light is generally known as difficult because of the limits of the current nano-fabrication technologies. To ease the fabrication, two metallic gratings, Al-air and Al-SiO₂ gratings, with periods slightly smaller than the DUV wavelength, were designed to exhibit an inverse polarizing effect, i. e. with TE transmittance largely exceeding TM transmittance. Both gratings were experimentally verified to possess inverse polarization transmission, whereas an enhanced TE transmission through Al- SiO₂ grating was observed. By using the Fourier modal method and the planar waveguide theory, we show that the strong coupling of the incident DUV wave to surface plasmons results in the minimum in TM transmittance, whereas the coupling to low-loss TE mode leads to the TE transmission through the grating region. By conformally filling the grating slits with the substrate dielectrics-SiO₂, the effective refractive index of the TE guided mode approaching that of the substrate greatly reduces the reflection of the mode at the grating-substrate interface. Thus, the TE transmittance of Al- SiO₂ grating is largely enhanced compared with Al-air case. At the DUV lithographic wavelength-193 nm, the measured inverse polarization extinction ratio of Al-SiO₂ grating is 103, suggesting itself a qualified compact polarizer for ArF 193 nm lithography system.