Widely tunable refractive index silicon nitride films deposited by ion-assisted pulsed DC reactive magnetron sputtering

Abstract

Silicon nitride films were deposited by ion-assisted pulsed DC reactive magnetron sputtering, where the regulation of power on the refractive index was emphasized. The power of the ion source and target was found to affect the refractive index. Refractive indices ranged from 2.13 to 2.63 (@632 nm) at ion source powers of 150, 300, 450, and 600 W, and from 2.45 to 3.02 (@632 nm) at target powers of 800, 1000, and 1200 W. The refractive index range was further extended to 1.89–3.02 (@632 nm) by co-adjustment, and extinction coefficients remained low in the visible to near-infrared band. The composition of deposited amorphous silicon nitride films varies with power, covering nitride-rich to silicon-rich. With no obvious defects on the surface and cross-section, the roughness slightly decreased with power, and the minimum roughness recorded was only 0.12 nm. In this work, a method for depositing silicon nitride films with a widely tunable refractive index range was proposed, which is promising for the application of optical thin films and waveguides.