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 (AlO
x
) films. For the activation of surface passivation, the films were subjected to post deposition annealing (PDA) in different ambients namely N
₂
, N
₂
+ O
₂
, 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 N
₂
or N
₂
+ O
₂
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 AlO
x
is suggested based on cross-sectional transmission electron microscopy and X-ray photoelectron spectroscopy analysis and electrical data.