Humidity degradation and repair of ALD Al2O3 passivated silicon

Abstract

The effect of humidity on boron diffused and undiffused silicon samples passivated by aluminum oxide (Al₂O₃) synthesized by plasma-assisted atomic layer deposition (PA-ALD) has been investigated. We found that undiffused samples show a higher degradation rate than diffused samples. Under an ambient of 100% relative humidity and 50°C, the lifetime of an undiffused sample passivated by Al₂O₃ decreased from 1500 to 400μs after 28 hours of exposure, whereas the saturation current density of the diffused region J_op+ of a boron diffused sample was nearly unchanged after 7 days of exposure. As expected, for both diffused and undiffused samples, the degradation rate is accelerated by increasing the temperature of the humidity environment. A PECVD SiN_x, capping layer acts as an effective protection layer for Al₂O₃ to resist a damp-heat conditions of 100% relatively humidity at 80°C. The electrical resistance of PA-ALD Al₂O₃ was observed to degrade in humidity. Fourier Transform Infra-red Spectroscopy (FTIR) measurements indicate that damp heat results in a structural modification of the bulk Al₂O₃ film and the formation of AlO(OH). This change could be responsible for the fast degradation rate of PA-ALD Al₂O₃ passivation compared with SiO₂. Finally, we experimentally demonstrated that the degraded passivation of an Al₂O₃ layer can be repaired by light illumination and negative corona charge deposition.