LOW-TEMPERATURE EPITAXIAL-GROWTH MECHANISM OF SI1-XGEX FILMS IN THE SILANE AND GERMANE REACTIONS

Low-temperature epitaxial growth of undoped and doped Si1-xGex films o n the Si(100) surface at 550 degrees C was investigated under the clea nest possible reaction environment of SiH4, GeH4 and H-2 with the PH3 or B2H6 addition using an ultraclean hot-wall low-pressure chemical va pour deposition (LPCVD) system. The SiH4 and GeH4 reaction rates are e xpressed by the Langmuir-type rate equation, assuming that one SiH4 or GeH4 molecule is adsorbed at a single adsorption site, according to t he Langmuir's adsorption isotherm, and decomposes there. It is found t hat the SiH4 and GeH4 adsorption rate constants become larger at the b ond site of the Si-Ge pair than those at the others, while the SiH4 su rface reaction rate constant becomes the largest at the bond site of t he Ge-Ge pair. With the PH3 and B2H6 addition, the incorporation rate of P and B increased proportionally and was higher with a higher Ge fr action x in the film. This was explained by the increase of the free s ite density and the difference of free site materials according to the Langmuir-type rate equation. In the case of P doping, it is found tha t electrically inactive P is formed with high Ge fractions.