Effects of Pre-annealing on Firing Stability of Atomic Layer-Deposited Al2O3

Abstract

Al2O3 layers fabricated with atomic layer deposition (ALD) show high levels of surface passivation on p- and n-type silicon wafers. In order to form front and rear electrodes, Al2O3 layers should undergo a firing process at a high peak temperature. Therefore, the Al2O3 layer must be stable under these conditions to maintain a high level of surface passivation during the firing process. In this study, Al2O3 layers fabricated with ALD were pre-annealed to enhance their thermal stability during the firing process. From quasi-steady state photoconductance (QSSPC) measurements, the difference between the implied V-oc values of the pre-annealed and fired samples was found to be smallest (3mV) when the sample was pre-annealed at 620 degrees C. The surface recombination rate calculated from capacitance-voltage (C-V) measurements of metal-Al2O3-Si (metal-insulator-semiconductor) structures was shown to be low when the sample was pre-annealed at 600-650 degrees C. Thus, firing stability was achieved with pre-annealing at 620 degrees C by reducing the surface recombination rate. We conclude that it is necessary to pre-anneal the Al2O3 passivation layer at this specific temperature to reduce the degradation of the passivation quality of Al2O3 after the firing process.