Passivation of a (100) Silicon Surface by Silicon Dioxide Grown in Nitric Acid

Abstract

This letter investigates silicon dioxide layers grown at low temperature in concentrated nitric acid using a two-step process developed by Imai et al for thin-film transistors. With photoconductance measurements, we find that, prior to an anneal, nitric acid oxidation does not passivate the silicon surface, but, after a 30-min nitrogen anneal at 1100 °C, a surface recombination velocity (SRV) of 107 cm/s (at Δn = 1015 cm-3) is attained on 1-Ω · cm n-type silicon. The SRV is further decreased to 42 cm/s after a 30-min forming gas anneal (FGA) at 400 °C, which is equivalent to a thermal oxide under similar annealing conditions, although it is not stable and returns to its pre-FGA state over time. Capacitance-voltage and photoconductance measurements suggest that the oxides contain a high positive fixed charge-particularly after a 1100 °C N2 anneal-which aids the passivation of n-type and intrinsic silicon but harms the passivation of low-resistivity p-type silicon.