High-Level Silicon Surface Passivation by Anodically Grown Silicon Dioxide and Silicon Nitride Stacks

We investigate the surface passivation attained by a stack consisting of anodically grown silicon dioxide and silicon nitride. A very low surface saturation current density J(os) of 3 fA/cm(2) is attained after the silicon wafers are submersed in nitric acid under a constant bias for >30 min, followed by a silicon nitride deposition and subsequent annealing in forming gas (FG) at 400 degrees C. We examine J(os) as a function of the anodic SiO2 thickness (d(ox)) and show that for d(ox) between 7 and 36 nm, J(os) decreases monotonically from 32 to 3 fA/cm(2), respectively. From capacitance-voltage (CV) and conductance measurements, we show that this reduction in J(os) with an increase in oxide thickness primarily results from a reduction in both the interface defect density (D-it) and the hole capture cross section (sigma(p)). For the lowest J(os) of 3 fA/cm(2), a low D-it of similar to 2.0 x 10(10) cm(-2).eV(-1) and a low sigma(p) of similar to 1 x 10(-16) cm(-2) are determined. When the anodic SiO2 films are capped by a silicon nitride film, negligible surface passivation degradation occurs, in comparison with uncapped anodic SiO2 films. Finally, we demonstrate that thermally induced bulk silicon defects can be eliminated by replacing high temperature (1000 degrees C) oxidations with a room-temperature anodic oxidation technique.