Diffusion of hydrogen atoms in silicon layers deposited from molecular beams on dielectric substrates

Abstract

In the paper, the processes occurring during low-temperature growth of non-hydrogenated amorphous Si and polycrystalline Si films on multilayer Si3N4/SiO2/c-Si substrates from molecular beams under conditions of ultrahigh vacuum are studied in detail. Diffusion of hydrogen atoms from a dielectric layer into the growing film is shown to accompany the growth of a silicon film on a Si3N4 layer deposited by CVD or on a SiO2 layer obtained by thermal oxidation of a silicon wafer. The process of hydrogen migration from the dielectric substrates into the silicon film is studied using FTIR spectroscopy. The reduction of IR absorption at the bands related to the N[sbnd]H bonds vibrations and the increase of IR absorption at the bands relating to the Si[sbnd]N bonds vibrations in IR spectra demonstrate that hydrogen atoms leave Si3N4 layer during Si deposition from a molecular beam. The absorption band assigned to the valence vibrations of the Si[sbnd]H bond at ∼2100 cm–1 emerging in IR spectra obtained at samples deposited both on Si3N4 and SiO2 layers indicates the accumulation of hydrogen atoms in silicon films. The difference in chemical potentials of hydrogen atoms in the dielectric layer and the silicon film explains the transfer of hydrogen atoms from the Si3N4 or SiO2 layer into the growing silicon film.