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 degrees C for 4 h or 8 h followed by stabilization at 780 degrees C for 3 h, and growth at 1000 degrees 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 degrees 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 degrees 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 x 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 x 1022 cm-3.