Investigation of the impact of amorphous silicon layers deposited by PECVD and HDP-CVD on oxide precipitation in silicon

The effect of deposited a-Si layers with different layer stress on oxide precipitation was investigated in order to find out if intrinsic point defects affecting oxide precipitation are generated at the interface a-Si/Si and if possibly hydrogen affects the oxide precipitation. A thermal cycle of nucleation at 650 °C for 4 h or 8 h followed by stabilization at 780 °C for 3 h, and growth at 1000 °C for 16 h was applied. It was found that there are no signs for the injection of intrinsic point defects from the interface a-Si/Si into the Si substrate during the applied thermal treatment. However if a-Si is deposited on 1000 nm silicon oxide, deposited previously from TEOS in a plasma process, silicon self-interstitials seem to be injected from the interface silicon oxide/Si into the silicon substrate retarding oxide precipitation in the initial stage of nucleation annealing at 650 °C. There are also no signs of any impact of the layer stress on oxide precipitation or self-interstitial injection. The concentration of hydrogen in the layers can be controlled via the RF bias power. The hydrogen concentration is reduced markedly already during annealing at 650 °C. Part of the hydrogen diffuses into the silicon substrate and enhances oxide precipitation if its initial concentration in the layers is higher than 1.5 × 1022 cm−3. For a-Si deposited on 1000 nm silicon oxide, the enhancement effect appears for hydrogen concentrations in the layer higher than approximately 2.8 × 1022 cm−3.