Design, fabrication, and characterisation of wire grid polarizers for the deep UV spectral range

In this communication, we show preliminary results on transmissive TiO₂ wire-grid polarizers (WGP) operating in the deep ultraviolet (DUV) range. WGP are devices based on strips of materials with large values of the modulus of the dielectric constant along with high absorption in the operational range. The merit function Π is introduced as a new tool to find the optimum material for WGPs in a given spectral range. The experimental dielectric constant of TiO₂ thin films deposited by pulsed laser deposition are obtained through spectroscopic ellipsometry, and the Π function indicates that TiO₂ is the best candidate for WGP in the DUV range when it is compared with other oxides. Once the material selection for WGP is done, we present and compare two different design approaches for WGP: one using an effective medium theory for the periodic structure, and the second using finite-difference time-domain (FDTD) analysis. A prototype of WGP is fabricated by electron beam (e-beam) lithography followed by lift-off process; the topography of the sample is analyzed by AFM, and we found noticeable deviations in the grating from the designed values. In preliminary characterization work the effective dielectric constant in two perpendicular orientations is obtained by ellipsometry and the contrast is compared with the design.