On chemical vapour deposition of Si1-(x+y)GexBy thin films with very high and very low boron contents. III. Very low boron contents and the epitaxial state

Abstract

For part II see ibid., vol.9, p.1833 (1994). Total growth rate and composition data of Si1-(x+y)GexBy thin films grown from silane, germane, diborane and hydrogen gas mixtures at 550 degrees C and 30 Pa (Murota J, Yoshida T, Goto K, Maeda T, Aitawa K and Sawada Y 1993 J. Physique IV Coll. C3 suppl. J. Physique II 3 427) are subject of a re-examination. Data are interpreted on the background of the previously developed 'three partial rates' model. As a result low-level boron doping (NB<5*1020 cm-3) during Si/Ge chemical vapour deposition is shown to be dominated by the increase of total layer growth rate due to the increase of the germane content of the gas phase up to about 60 at.% of germanium in the film. In consequence the boron content decreases down to about ten times less than that obtained in pure silicon films deposited without germane in the reaction gas mixture. In the range above 60 at.% of germanium in the film the boron content is nearly constant because the boron incorporation flux increases and the increase of total layer growth rate due to the increase of germane partial pressure is less steep. Total layer growth rate can be described in a first approach by neglecting the presence of diborane in the gas phase as well as that of boron in the film.