Effects of thin film deposition rates, and process-induced interfacial layers on the optical properties of plasma-deposited SiO2/Si3N4 Bragg reflectors

Abstract

Highly reflecting dielectric multilayer stacks, also designated as Bragg reflectors (BRs) have been fabricated using SiO2 and Si3N4 layers prepared by remote plasma-enhanced chemical-vapor deposition (RPECVD). Departures from the reflectance spectrum of a perfectly periodic bilayer structure with nondispersive dielectric materials results from (i) intrinsic effects associated with dispersion in the dielectric constants of the constituent layers, and (ii) extrinsic effects that are a result of departures from ideal bilayer geometry. Model calculations have shown that extrinsic effects in the optical response of BRs prepared by RPECVD derive from (i) systematic increases in nitride film thickness with increasing stack thickness, and/or (ii) from nonideal optical thicknesses in which the individual layers do not have an optical path length (OPL) equal to one-quarter of the wavelength at the center of the first low photon energy reflectance band, λ/4, but instead maintain a periodic structure in which the sum of the two OPLs equals λ/2.