SILICON-NITRIDE THIN-FILM PRODUCTION ON SI(111)

The production of silicon nitride films by ammonia decomposition Si(111)-(7X7) has been studied by high-resolution electron energy loss spectroscopy, Auger electron spectroscopy, and low-energy electron diffraction. Silicon nitride films of less-than-or-equal-to 1 monolayer thickness exhibit a characteristic four mode vibrational spectrum after annealing to 1200 K, while multilayer films produce three vibrational modes at 495, 720, and 1020 cm-1. Upon continued heating of the submonolayer and multilayer nitride films, identical vibrational spectra are obtained, suggesting that both layers form Si3N4. These results are in excellent agreement with the vibrational spectra reported in the literature for Si3N4 layers grown using N atoms on the heated Si(111)-(7X7) surface, signifying that identical nitride films can be grown using ammonia. Si3N4 films grown on Si (111) are able to chemisorb ammonia at 300 K, showing that coordinatively unsaturated silicon sites are probably present on the film surface. This is in agreement with other studies which indicate that the growth mechanism for these silicon nitride films involves silicon enrichment at the film/vacuum interface.