Microscopic and elemental analysis of temperature-induced changes in sulfur/silicon nitride stack-passivated Si surface

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Sulfur passivation of different Czochralski Si surfaces along with hydrogenated amorphous silicon nitride capping layer has been reported. The effect of capping layer thickness and deposition temperature on sulfur reacted surface has a strong effect on initial passivation quality and its stability. Sulfur passivation on phosphorus diffused n-type textured Czochralski Si wafers capped with a 100 nm stacked hydrogenated amorphous silicon nitride layer demonstrates improved stability under heat and light with saturation current density <80 fA/cm2. A stack layer of a low temperature (≤300OC) hydrogenated amorphous silicon nitride followed by a high temperature (≈ 450OC) hydrogenated amorphous silicon nitride is adopted to achieve good thermally stable surface passivation. Sulfur-passivation with only a low temperature hydrogenated amorphous silicon nitride capping layer exhibits unstable behavior after thermal treatment due to blister/pinhole formation at ≥300OC and possible oxidation of the S-passivated surface. Photoluminescence imaging shows increased defect recombination loss due to disrupted surface passivation after thermal treatment. Fourier transform infrared spectroscopic studies demonstrate that these blister formations were caused by hydrogen effusion from Si–H and N–H bonds dissociation upon thermal processing. Time of flight secondary ion mass spectroscopy exhibits oxidation of S-reacted surface after thermal treatment that degrades the passivation quality.