Study of the passivation mechanism of c-Si by Al2O3 using in situ infrared spectroscopy

We present an in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy study of the passivation mechanism in the surface passivation of Si solar cells by Al₂O₃ thin films deposited via atomic layer deposition (ALD) using TMA and O₃ as precursors. The IR measurements suggest that during the annealing stage, the Si-H bonding near the interface decreases. We have used D-terminated c-Si internal-reflection crystals to differentiate the residual H atoms that may migrate from ALD Al₂O₃ films versus the residual D atoms present at the Al₂O₃/c-Si interface after ALD. Within the sensitivity of the ATR-FTIR spectroscopy setup of ~10¹² cm^-2 for Si-H bonds, we do not detect any migration of H from Al₂O₃ to the c-Si interface. Therefore, we conclude that the migration of O, and the subsequent restructuring of the interface during the annealing step, primarily contributes toward the chemical passivation of the Al₂O₃/c-Si interface.