Role of mobile hydrogen in the amorphous silicon recrystallization

Abstract

The plasma deposition of nanocrystalline silicon thin films is usually performed under a high flux of atomic hydrogen and hydrogenated chemical species. The growth mechanisms are investigated using the layer-by-layer deposition of dense nanocrystalline silicon, obtained at 250 °C by alternating SiH4 and H2 plasmas. In the steady state, a minimum exposure time to the hydrogen plasma is necessary to recrystallize the amorphous top layer (10–85 Å). It is shown that this critical time is determined by the diffusion time of some mobile H through the top a-Si:H layer. The recrystallization is discussed in relation to the diffusion of hydrogen leading to the nanovoid and broken bond formation processes.