Observation of phosphorus pile-up at the SiO2-Si interface

The Si oxidation rate at high temperatures is increased by heavy P doping. Sputter ion-Auger techniques have been used to investigate the oxide thickness and P concentration after 900 °C oxidation with an initial P surface concentration of between 2×1018 and 3.2×1020/cm3. Phosphorus was found to pile up in the Si-SiO2 interface region. The maximum P concentration near the interface was found to depend on doping and was (at certain P concentrations) an order of magnitude larger than that predicted by redistribution theory. A vacancy–P-complex model is presented to explain the observed behavior. A correlation between the selective pile-up of P at the interface and the current gain of planar bipolar transistors is reported.