Growth mechanisms of crystallites in the mixed-phase silicon films deposited by low-pressure chemical vapor deposition

Abstract

The microstructure and growth mechanisms of mixed-phase silicon films deposited on glass substrates by infra-low pressure chemical vapor deposition and low pressure chemical vapor deposition using 20% Si2H6/He gas have been investigated by X-ray diffraction and cross-section transmission electron microscopy. The deposition temperature and pressure were in the range of 560-600 degreesC and below 10 mtorr, respectively. In mixed-phase films, there were two kinds of crystallites: initially deposited pre-existing small irregular (311)-preferred crystallites and conventionally incubated (111)-preferred large elliptic bulk-induced crystallites. The behavior of the former changed depending on the deposition conditions of temperature and pressure. Just above the deposition rate below which a (110) polysilicon film formed, (311)-preferred quasi-columnar growth occurred by surface-induced crystallization. This quasi-columnar growth preserved or strengthened the initial (311) preference and grew with an activation energy of 3.1 eV. A further increase of deposition rate made it difficult to form quasi-columnar growth due to a smaller nucleation density and because surface-induced crystallization was suppressed. Then conventional bulk-induced crystallization became dominant to form a (111) preferred mixed-phase films. (C) 2000 Elsevier Science S.A. All rights reserved.