Quasicontinuous refractive index tailoring of SiNx and SiOxNy for broadband antireflective coatings

Abstract

A broadband antireflective coating for silicon was fabricated by tailoring the compositions of SiNx and SiOxNy during conventional plasma enhanced chemical vapor deposition. The coating’s refractive index was quasicontinuously graded, e.g., from 3.22 to 1.44 at 1550 nm. Over the 280–3300 nm wavelength range, the reflectance was below 8% peak and 4.3% average. The deposited stack was composed of dense dielectric materials. This enables patterning and processing into robust devices after coating deposition. Using single layer ellipsometry data, the transfer matrix method was applied to predict the multilayer coating’s reflectance spectra. The results showed good agreement with experimental data.