Modelling of 18O tracer studies of the oxygen redistribution during formation of SiO 2 layers by high dose implantation

Abstract

The modelling of buried SiO 2 layer formation by high dose implantation is extended to simulate new experimental data. The experiments involved the implantation of two different oxygen isotopes ( 16O and 18O) followed by subsequent analysis by secondary ion mass spectroscopy (SIMS) to determine the isotope distributions. The model contains all the essential features of the original formulation such as the inclusion of volume swelling due to silicon oxidation, sputtering and the diffusion of excess oxygen within the SiO 2, but has now been enhanced to include (a) the two oxygen isotopes and (b) the observed phenomenon of perfect isotopic exchange between migrating oxygen and matrix oxygen within the layer. Using the model, isotope depth distributions have been generated for comparison with the experimental data. For doses lower than the critical dose needed for layer formation, profiles have been calculated showing the distribution of the two isotopes. For the case where the combined dose is greater than this critical dose good agreement is found between the experimental data and the distributions calculated. Some discrepancies are apparent especially at the edges of the buried layer which originate in the non-linearity of the SIMS signals.