Aluminum Oxide Deposited by Pulsed-DC Reactive Sputtering for Crystalline Silicon Surface Passivation

In this paper, we report on the surface passivation of crystalline silicon (c-Si) by pulsed-dc (p-dc) reactive-sputtered aluminum oxide (AlOx) films. For the activation of surface passivation, the films were subjected to post deposition annealing (PDA) in different ambients namely N₂, N₂ + O₂, and forming gas (FG) in the temperature range of 420-520°C. The surface passivation was quantified by surface recombination velocity, which was correlated to the interface states at the silicon-dielectric interface and fixed charges in the dielectric. A good quality surface passivation with effective surface recombination velocity S_eff of 41 cm · s^-1 is obtained for PDA in N₂ or N₂ + O₂ gas ambient. PDA in FG ambient at high temperature is found to degrade the passivation. The AlO_x film annealed in FG ambient shows poorer thermal stability as compared with films annealed in the other two ambients. A clear path for further improvements in surface passivation quality of p-dc reactive sputter-deposited AlOx is suggested based on cross-sectional transmission electron microscopy and X-ray photoelectron spectroscopy analysis and electrical data.