Substrate Potential Dependence of Optical Characteristics of a-Si:H for Shortwave Near-infrared Filter by DC and RF Sputtering

Abstract

In this study, the substrate potential dependence of the film structures and optical characteristics of hydrogenated amorphous silicon (a-Si:H) prepared by reactive sputtering was investigated for application in short-wave near-infrared band pass filters (BPFs). During direct current (DC) sputtering, the substrate was charged to a negative potential, which was further increased by applying an RF bias. When the negative potential was large owing to the bias, the surface of the film became smooth owing to the ion bombardment. However, the refractive indices of the films decreased as the Si−H2 bonds increased. When radio frequency (RF) sputtering was used, the acceleration voltage of the ions decreased to 1/3; thus, structural relaxation was promoted. Consequently, a-Si:H with a high refractive index, low optical absorption, and high thermal durability, which are suitable for a narrow BPF, was obtained. The deterioration after annealing of the characteristics of the BPF using a-Si:H prepared by RF sputtering was reduced by half compared with DC sputtering.