Surface Morphologies of Hydrogenated Amorphous Silicon at the Early Stages of Plasma-Enhanced Chemical Vapor Deposition

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Abstract
Ultrathin hydrogenated amorphous silicon (a-Si:H) films have been deposited on atomically flat, hydrogen-terminated Si(111) surfaces. The film morphologies have been studied by atomic force microscopy (AFM) with a vertical resolution of 0.01 nm. The film surfaces of 1.0-5.0 nm thick a-Si:H deposited at 200° C on flat Si(111) substrates reveal terraces and biatomic steps of the initial Si(111) 1×1: H surface and the average microroughness remains unchanged regardless of the film thickness. In the case of a-Si:H deposition on 1.7-nm-thick SiO2 thermally grown on flat Si(111) or 2.0-nm-thick a-Ge:H on Si(111), the a-Si:H surface morphology also maintains the atomic step structure of the substrate. This indicates that a-Si:H deposition occurs via a layer-by-layer mechanism.