Kinetic roughening of amorphous silicon during hot-wire chemical vapor deposition at low temperature

We use postdeposition atomic force microscopy and in situ spectroscopic ellipsometry to analyze the roughening of hydrogenated amorphous silicon films deposited by hot-wire chemical vapor deposition at 150°C. From the atomic force microscopy data, the root-mean-squared roughness w increases with deposition time t as w∝tβ with β=0.37±0.02, and the correlation length ξ increases as ξ∝t1∕z with 1∕z=0.31±0.02. From the height-difference correlation function, we obtain a roughness exponent α=0.87±0.04 and a root-mean-squared local slope δ, which increases as δ∝tκ with κ=0.17±0.03. These measurements are indicative of anomalous growth, which we attribute to geometric shadowing. However, the roughening behavior we observe using atomic force microscopy is not reproduced in the spectroscopic ellipsometry data. This contradicts previous reports which found a linear relationship between the thickness of the optical roughness layer and the root-mean-squared roughness. We discuss the discrepancy between the two techniques in terms of short-range roughness and vector perturbation theory.