The dependence on the substrate temperature and the flux rates of the behavior of impinging elemental Si and Ge fluxes on a SiO2 surface. including SiO2 etching and the deposition of polycrystalline Si and SiGe films, was investigated by using the solid source molecular beam epitaxy (MBE). Flux rates of the source beams and a substrate temperature were in the range of 1 to 5 X 10(13) atoms/cm2s and 710-810-degrees-C, respectively. Under these experimental conditions, the Ge flux was not individually effective to etch the SiO2, but contributed to etching the oxide layer with an accompanying Si flux. The critical flux of Si for SiO2 etching at 740-degrees-C was determined to be about 1 X 10(13) atoms/cm2s.