Comparing the Optical Characteristics of Dielectric Mirrors Fabricated by PECVD from Different Precursors: Monosilane and Tetraethoxysilane

Abstract

The influence of the application of silicon oxide produced from a gas precursor, i.e., monosilane SiH₄ and an organosilicon precursor, i.e., tetraethoxysilane (TEOS) on the optical characteristics of dielectric Bragg mirrors is compared. The use of tetraethoxysilane as a precursor in plasma-enhanced chemical vapor deposition (PECVD) demonstrates a decrease in the average roughness of the deposited film. The same method of film deposition also makes it possible to fabricate a SiN_x/SiO_x pair in one process chamber without breaking vacuum. It is experimentally shown that a mirror fabricated from a TEOS precursor possesses better characteristics than a mirror fabricated using monosilane, thus, the reflectivity increases by 20% and optical losses decrease twofold. The roughness average R_a of the surface of a SiN_x/SiO_x (TEOS) mirror decreases fivefold when compared to a SiN_x/SiO_x (SiH₄) mirror. The application of a TEOS precursor substantially increases the quality of the interfaces of the deposited layers which leads to a gain in the reflectivity of the Bragg mirror and a decrease in the roughness average R_a from 11.04 down to 2.31 nm. As a consequence, improvement of the SiN_x/SiO_x interfaces leads to a twofold reduction in the losses. These results can be considered as a significant advantage that leads to a drop in the costs of materials during the fabrication of multilayer mirrors.