Surface Mechanisms in Low-Temperature Plasma Deposition of Silicon

Abstract

Dynamic scaling of surface roughness evolution during plasma deposition of amorphous silicon is utilized to characterize surface transport mechanisms. Different surface transport mechanisms leave distinct imprints in the surface that can be distinguished through fractal analysis. Surface roughness is characterized using atomic force microscopy (AFM) and the static and dynamic scaling coefficients a and b and the lateral correlation length Lc are extracted from the evolution of surface roughness and are used to identify surface mechanisms. Values of a = 1.0 and b = 0.3 have been obtained, which reveal that surfaces are smoothed through surface diffusion during film growth. Temperature dependence of the Lc is used to calculate diffusion barriers with values around 0.2 eV, consistent with the diffusion of a weakly bound physisorbed species. The effects of process conditions such as substrate temperature, diluent gases composition, process pressure, RF power density, and reactor configuration on the scaling parameters have been investigated. An amorphous silicon kinetic growth model has been developed that incorporates surface coverage dependent diffusion barriers. The model reproduces most experimentally observed results, although some deposition conditions are identified where the model is not valid.