Variation of passivation behavior induced by sputtered energetic particles and thermal annealing for ITO/SiO_x/Si system

The damage on the atomic bonding and electronic state in a SiO_x(1.4-2.3 nm)/c-Si(150 μm) interface has been investigated. This occurred in the process of depositing indium tin oxide (ITO) film onto the silicon substrate by magnetron sputtering. We observe that this damage is caused by energetic particles produced in the plasma (atoms, ions, and UV light). The passivation quality and the variation on interface states of the SiO_x/c-Si system were mainly studied by using effective minority carrier lifetime (τ_eff) measurement as a potential evaluation. The results showed that the samples' τ_eff was reduced by more than 90% after ITO formation, declined from 107 μs to 5 μs. Following vacuum annealing at 200℃, the τ_eff can be restored to 30 μs. The components of Si to O bonding states at the SiO_x/c-Si interface were analyzed by x-ray photoelectron spectroscopy (XPS) coupled with depth profiling. The amorphous phase of the SiO_x layer and the “atomistic interleaving structure” at the SiO_x/c-Si interface was observed by a transmission electron microscope (TEM). The chemical configuration of the Si-O fraction within the intermediate region is the main reason for inducing the variation of Si dangling bonds (or interface states) and effective minority carrier lifetime. After an appropriate annealing, the reduction of the Si dangling bonds between SiO_x and near the c-Si surface is helpful to improve the passivation effect.