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

In this manuscript, we characterized SiO
2
/Al
2
O
3
(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 Al
2
O
3
(<1nm) we accomplished effective lifetimes <100 µs. By adding a thin SiO
2
(~1nm) layer prior to the Al
2
O
3
deposition, we improved the effective lifetime >500 µs. The SiO
2
layer enhances the chemical and field effect passivation by increasing hydrogen contents and negative fixed charge effect of the Al
2
O
3
. To increase further the effective lifetime, we added doped a-Si:H layers on top of the SiO
2
/Al
2
O
3
. 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 100µs 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 60µs to 10µs. After RTA the effective lifetime didn’t change significantly.