On the Impact of Strained PECVD Oxide Layers on Oxide Precipitation in Silicon

Abstract

PECVD oxide layers with different layer stress ranging from about −305.2 MPa to 39.9 MPa were deposited on silicon wafers with similar concentration of interstitial oxygen. After a thermal treatment consisting of rapid thermal annealing (RTA) and furnace annealing 780°C 3 h + 1000°C 16 h in nitrogen the profiles of the oxide precipitate density were investigated. Supersaturations of self-interstitials as function of layer stress were determined by adjusting modelling results to measured depth profiles of bulk microdefects. The self-interstitial supersaturation generated by RTA at 1250°C and 1175°C at the silicon/oxide interface is increasing linearly with increasing layer stress. Values for self-interstitial supersaturation determined on deposited oxide layers after RTA at 1250°C and 1175°C are very similar to values published for RTO by Sudo et al. An RTA at 1175°C with a PECVD oxide on top of the wafer is a method to effectively suppress oxygen precipitation in silicon wafers. Nucleation anneals carried out at 650°C for 4 h and 8 h did not show any effect of PECVD oxide layers on oxide precipitate nucleation.