SiO2/Si Interfacial Degradation and the Role of Oxygen Interstitials

Overview & Synopsis

High temperature annealing of Si/SiO2/Si structures in inert atmospheres is known to result in degradation of the oxide layer and electron and hole trap creation. We review our understanding of the basic mechanisms active in such structures that can result in point defect generation. Using electron spin resonance and infra-red absorption data, we demonstrate that in low oxygen content Si substrates (float zone) annealing of Si/SiO2/Si structures at high temperatures results in a gettering of oxygen from the oxide into interstitial sites in the Si substrate. Oxygen vacancy centres are left in the oxyde. This behaviour is well accounted for by a diffusion model in which oxygen diffuses out of the oxide, into the Si, the driving force this motion is the temperature dependent solubility limit of oxygen in Si. This mechanism should be active in float zone substrates for essentially all temperatures $\gtrsim 700~^{\circ}$C. For high oxygen content substrates (Czochralski grown) we also observe oxygen vacancy creation in the oxide when very high temperature annealing is performed ($\sim 1320~^{\circ}$C). However, for these substrates at lower temperatures which are more “technological” ($\sim 1000~^{\circ}$C) we anticipate that dissolved O interstitial diffusion to the Si/SiO2 interface and percipitation of SiO2 platelets in the bulk will be the prime mechanisms to be considered.