Al-neal degrades Al${}_2$O${}_3$ passivation of silicon surface

Atomic layer deposited (ALD) aluminum oxide (Al${}_2$O${}_3$) 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 Al${}_2$O${}_3$ films tolerate the so-called Al-neal treatment that is a necessary process step in devices that also contain silicon dioxide (SiO${}_2$) passivation layers. Herein, it is reported that the Al-neal process is harmful for the passivation performance of Al${}_2$O${}_3$ 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 Al${}_2$O${}_3$ 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${}_x$/Al${}_2$O${}_3$ interface. The root causes for the defect reactions are discussed and possible reasons for the observed phenomena are suggested. (© 2021 The Authors. physica status solidi (a) applications and materials science published by Wiley‐VCH GmbH)