Modulation of dielectric film on two-axis Lloyd's mirrors for patterning high-uniformity nanoscale grating

Periodic nanoscale array structures are of great importance in various fields including photonic crystals, diffraction gratings, etc. In this study, a dielectric-film-based polarization modulation scheme on an orthogonal two-axis Lloyd's mirrors interference system was proposed for patterning high-uniformity nanoscale two-dimensional (2D) grating over a large area. We established a beam reflection model of three media-layer structure of air-dielectric film (MgF2)-metal substrate (Al) and calculated the integrative amplitude reflection coefficients. We systematically analyzed the spatial polarization states of the interference beams and determined the optimal exposure conditions to automatically eliminate the additional interference at certain incident angles. We plotted the optimal period of fabricable 2D grating at different thickness of dielectric film MgF2, where a thickness of 66.3 nm was selected for experimental demonstration. Then, 2D gratings with various periods of 740 nm, 780 nm, 1000 nm, and 1250 nm were fabricated, which presented a high consistency with the simulation results and revealed the fabrication ability over a period range from 730 nm to 840 nm. This dielectric-filmbased polarization modulation mechanism enables to extend the fabricable 2D grating with a smaller pitch, which is corresponding to a larger area. The proposed dielectric-thin-film-based polarization modulation mechanism provides a promising approach for fabricating large-area, high-uniformity, 2D-crossed gratings with a high throughput.