The growth of thin oxides on a-Si and a-Si:H in an O2 plasma

Abstract

We have used in situ and spectroscopic ellipsometry measurements to study the growth of thin oxide layers on the surface of both unhydrogenated and hydrogenated amorphous silicon (a-Si and a-Si:H) using an oxygen rf discharge. Spectroscopic ellipsometry data were taken on samples both before and after oxide growth to derive the maximum information about the surface structure of the films. In situ single wavelength ellipsometry measurements taken during plasma oxidation showed that the growth curves were nearly identical for glow discharge a-Si:H and both ion-beam sputtered a-Si and a-Si:H. The initial stages of oxide growth could not be easily fit to a model of uniform or planar growth, probably because of a surface modulation or roughness which exists on the film before growth. Further growth appeared to follow, or at least approach, a layer-by-layer process. The thickness of the surface roughness layer on the a-Si:H before growth matched that observed at the oxide/a-Si:H interface after growth. For oxide thicknesses greater than 10–20 Å, the growth rate is consistent with a diffusion limited model. Under our plasma conditions, the diffusion coefficient of the plasma species through the oxide is 2.1×10−17 cm2/s for all samples.