Line-edge roughness as a challenge for high-performance wire grid polarizers in the far ultraviolet and beyond

Abstract

High-performance nano-optical elements for application wavelengths in the ultraviolet spectral range often require feature sizes of only a few tens of nanometers where line edge roughness (LER) becomes a critical parameter for the optical performance. In this contribution, we explore the influence of LER on the optical performance of wire grid polarizers (WGP) in the far ultraviolet range. Therefore, we present a method, which uses the finite difference time domain method in combination with a comprehensive spatial frequency dependent LER model. The measured LER of 3.6 nm (standard deviation) reduces the WGP's extinction ratio by a factor of 3.6 at a wavelength of 248 nm. We identify a critical range of the correlation length, which maximizes the detrimental effect of LER. The presented method and the results provide the basis for future fabrication technology optimization of WGPs and other optical meta-surfaces in the ultraviolet spectral region or at even shorter wavelengths.