Low-Temperature Epitaxial Growth Mechanism of Si1-xGex Films in the Silane and Germane Reactions

Abstract

Low-temperature epitaxial growth of undoped and doped Si 1-x Ge x films on the Si(100) surface at 550°C was investigated under the cleanest possible reaction environment of SiH 4 , GeH 4 and H 2 with the PH 3 or B 2 H 6 addition using an ultraclean hot-wall low-pressure chemical vapour deposition (LPCVD) system. The SiH 4 and GeH 4 reaction rates are expressed by the Langmuir-type rate equation, assuming that one SiH 4 or GeH 4 molecule is adsorbed at a single adsorption site, according to the Langmuir's adsorption isotherm, and decomposes there. It is found that the SiH 4 and GeH 4 adsorption rate constants become larger at the bond site of the Si-Ge pair than those at the others, while the SiH 4 surface reaction rate constant becomes the largest at the bond site of the Ge-Ge pair. With the PH 3 and B 2 H 5 addition, the incorporation rate of P and B increased proportionally and was higher with a higher Ge fraction x in the film. This was explained by the increase of the free site density and the difference of free site materials according to the Langmuir-type rate equation. In the case of P doping, it is found that electrically inactive P is formed with high Ge fractions.