Characterization of SiO2/Al2O3 stack passivation with n- and p-type poly-Si layers

In this manuscript, we characterized SiO2/Al2O3 (1nm/0.8nm) layers stacked with n-type polysilicon or p-type polysilicon. This study explores the surface passivation capabilities of these structures. In this work, we also optimized the rapid thermal annealing (RTA) in forming gas (N-2/H-2) environment. Using a very thin Al2O3 (<1nm) we accomplished effective lifetimes <100 mu s. By adding a thin SiO2 (similar to 1nm) layer prior to the Al2O3 deposition, we improved the effective lifetime >500 mu s. The SiO2 layer enhances the chemical and field effect passivation by increasing hydrogen contents and negative fixed charge effect of the Al2O3. To increase further the effective lifetime, we added doped a-Si:H layers on top of the SiO2/Al2O3. The doped a-Si:H layers are responsible to hydrogenate the stack. After depositing the n-a-Si:H, the effective lifetime was improved from 100 mu s to 1ms. After RTA the effective lifetime was increased to 4ms. When we deposited the p-a-Si:H, the effective lifetime was degraded from 60 mu s to 10 mu s. After RTA the effective lifetime didn't change significantly.