Atomic-scale analysis of plasma-enhanced chemical vapor deposition from SiH4/H2 plasmas on Si substrates

We present a systematic atomic-scale analysis of the interactions of SiH3 radicals originating in silane containing discharges with Si(001)-(2x1) and H-terminated Si(001)-(2x1) surfaces. Through simulations, we show that the hydrogen coverage of the surface is the key factor that controls both the surface reaction mechanism and the reaction probability. The SiH3 radical reacts readily with the pristine Si(001)-(2x1) surface during the initial stages of growth while its reactivity with the corresponding H-terminated surface is considerably lower. Deposition of a-Si:H from SiH3 radicals has also been simulated by repeatedly impinging SiH3 radicals onto Si(001)-(2x1) surfaces maintained at 500 degrees C. During deposition under these conditions, the dominant mechanism of hydrogen removal from the surface is through abstraction by SiH3 radicals, which subsequently return to the gas phase as silane. The important reaction processes that take place during film growth have been identified and their energetics has been analyzed.