In situ ellipsometric characterization and process control for amorphous thin film deposition

Abstract

Characterization of the growth of hydrogenated amorphous silicon (a-Si:H) and carbon (a-C:H) thin films by in situ ellipsometric analysis at 3.4 eV and 3.2 eV is reported. For a-Si:H, prepared on metal substrates from an rf discharge of SiH 4, in situ ellipsometry data are strongly influenced by the SiSi bond packing density in the growing film. Deviations in the data from model calculations assuming a thickness independent a-Si:H dielectric function, when analyzed using an effective medium approximation, reveal the geometry and scale of the initial nucleation process. Effects of the deposition conditions and substrate microstructure on the coalescence of initial nuclei are understood on the basis of new measurements. For a-C:H, prepared on c-Si substrates from CH 4 by direct ion beam deposition, ellipsometry measurements in the initial stages of growth provide monolayer sensitivity to the formation of an absorbing SiC x layer at the substrate interface. Fits to the data in the later stages of growth establish the real and imaginary parts of the bulk dielectric function at 3.2 eV, allowing real time categorization of the nature of the bonding in such films.