Al-neal Degrades Al₂O₃ Passivation of Silicon Surface

Atomic layer deposited (ALD) aluminum oxide (Al₂O₃) has emerged as a useful material for silicon devices due to its capability for effective surface passivation and ability to generate p⁺ region underneath the oxide as active or passive component in semiconductor devices. However, it is uncertain how Al₂O₃ films tolerate the so-called Al-neal treatment that is a necessary process step in devices that also contain silicon dioxide (SiO₂) passivation layers. Herein, it is reported that the Al-neal process is harmful for the passivation performance of Al₂O₃ causing over eightfold increase in surface recombination velocity (SRV) (from 0.9 to 7.3 cm s⁻¹). Interestingly, it is also observed that the stage at which the so-called activation of Al₂O₃ passivation is performed impacts the final degradation strength. The best result is obtained when the activation step is done at the end of the process together with the Al-neal thermal treatment, which results in SRV of 1.7 cm s⁻¹. The results correlate well with the measured interface defect density, indicating that the Al-neal affects defects at the Si/SiO_x/Al₂O₃ interface. The root causes for the defect reactions are discussed and possible reasons for the observed phenomena are suggested.