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 Voc values of the pre‐annealed and fired samples was found to be smallest (3 mV) when the sample was pre‐annealed at 620 °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 °C. Thus, firing stability was achieved with pre‐annealing at 620 °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.

Surface Passivation of Boron Emitters on n-Type Silicon Solar Cells

“…By comparing these results, it is observed that the Al 2 O 3 film shows increased negative fixed charge after the heat treatment. Similar results were reported in many papers [19][20][21][22][23]. According to these, the negative fixed charge of Al 2 O 3 results from its structural change.…”