In situ single wavelength ellipsometry studies of high rate hydrogenated amorphous silicon growth using a remote expanding thermal plasma

Abstract

An in situ single wavelength HeNe rotating ellipsometry study of high rate (∼80 ${\mathrm{\AA s}}^{\mathrm{-1}})$ hydrogenated amorphous silicon (a-Si:H) deposition using an expanding thermal plasma is presented. An optical growth model is used to simulate the measured ellispometric trajectories similar to models used for low rate a-Si:H growth in the literature. The in situ growth at high growth rates was studied as function of the substrate temperature. The refractive index n (at 632.8 nm) increases with increasing temperature corresponding to an increase in the density of the films. The in situ extinction coefficient k (at 632.8 nm) increases with increasing substrate temperature due to a smaller optical band gap and due to an increase in indirect absorption. It is shown that the ellipsometry setup in combination with optical modeling enables us to monitor the surface roughness evolution during deposition and to obtain the dynamic scaling exponent β for postinitial growth.