A Study on Surface Formation Mechanism by Molecular Beam Epitaxy (2nd Report)

An Effect of Substrate Orientation upon Si-Si Homo-Epitaxial Growth Mechanism

Abstract

Silicon (Si) substrates of five different kinds of crystal orientations are epitaxially grown to 10-120nm in thickness by a Si molecular beam epitaxy under a same growth temperature of 800°C. These epitaxially grown surfaces were observed at each grown thickness by the help of AFM interprocessly, thus their surface formation processes were clarified as follows. In the cases of (100) and (110) substrates, first, many micro nuclei, 20-50nm in height, were generated, secondly, they were gradually combined together, and finally, the ridge of them became smoother. In the cases of (113) and (331) substrates, the formation and combination processes of nuclei were also observed, however, further deposited molecules could not fill the spaces among the nuclei completely. In the case of (111) substrate, most of adsorbed molecules were caught at arbitrary atomic steps and contributed to extend the length of their terraces. The further growth made some steps piled, so that, higher steps and wider terraces were gradually generated, 1-5nm in height and 200-400nm in width. These surface formation processes can be explained, to some extent, from the surface energy level, namely, the higher energy tends to result in the higher nucleation density.