In situ investigation by IR ellipsometry of the growth and interfaces of amorphous silicon and related materials

The formation of amorphous silicon (a-Si:H) and silicon nitride (a-SiN_x) interfaces, and p-doped (p) and intrinsic (i) a-Si:H interfaces, was investigated in situ by IR phase modulated ellipsometry (IRPME). The monolayer sensitivity of IRPME to vibrational absorption is emphasized. In both cases, the nature of the interface is found to be strongly affected by the deposition sequence. The a-SiN_xa-Si:H and pi interfaces are found to be sharp. In contrast, different behaviour is observed when p-doped a-Si:H or a-SiN_x is deposited first. In the latter case, the IRPME measurement clearly reveal nitrogen incorporation in the first monolayers of a-Si:H. Likewise, hydrogen accumulation, at the level of a few monolayers, is observed at the ip interface.