Influence of a-Si:H Deposition Temperature on Surface Passivation Property and Thermal Stability of a-Si:H/SiN $_{x}$ :H Stack

The inability to withstand temperatures much above the deposition temperature without significant degradation has limited the application of hydrogenated amorphous silicon (a-Si:H) for surface passivation. To address this limitation, in this paper, the surface passivation quality and thermal stability of a stack-passivating system, combining a layer of intrinsic amorphous silicon and a capping layer of silicon nitride (SiN_x:H), on p-type crystalline silicon wafers is studied for different deposition temperatures for the underlying a-Si:H layer. Both effective minority carrier lifetime τ_eff measurement and Fourier transform infrared spectrometry were employed to study the passivating quality and thermal stability of the a-Si:H/SiN_x:H stacks. It is established that the lowest a-Si:H deposition temperature (160°C in this study) could result in improved as-deposited surface passivation but degrade quicker under an excessive thermal budget compared with layers with higher deposition temperatures. The more dihydride-rich film composition deposited at lower temperature is suggested to be beneficial for bond restructuring by hydrogen interchanges; however, it is also more susceptible to the provision of channels for hydrogen out-effusion, which could be responsible for the poorer thermal stability compared with stacks with underlying a-Si:H deposited at higher temperature.