Self-bias voltage diagnostics for the amorphous-to-microcrystalline transition in a-Si:H under a hydrogen-plasma treatment

The authors demonstrate the possibility of using self-bias voltage on the radio-frequency electrode of a capacitively coupled deposition system as a diagnostic tool to detect the amorphous-to-microcrystalline silicon transition during the exposure of a-Si:H thin films to a hydrogen plasma. This is achieved by combining self-bias voltage (Vdc) and kinetic-ellipsometry measurements, which provide real-time information on the film properties. On intrinsic and n -type a-Si:H films, the hydrogen-plasma exposure results in the formation of a hydrogen-modified layer, which is accompanied with a decrease in the absolute values of Vdc, until a plateau corresponding to the nucleation and the growth of the microcrystalline layer occurs. On p -type a-Si:H, the amorphous-to- microcrystalline transition is characterized by a rapid increase in the absolute values of Vdc. This particular trend is ascribed to the effects of boron on both the solid and plasma phases.