Improved understanding and characterisation of rapid thermal oxides

Rapid thermal oxidation (RTO) was studied in dependence of processing time, processing temperature and diffusion profile of the surface to be oxidised in Si solar cell production. Experiments were performed on conventionally phosphorous-diffused Si substrates. Sheet resistance values as well as SIMS and SRP profiles were compared before and after RTO. Oxide thicknesses were measured by ellipsometry. The RTO oxide structure was analysed by ESCA and AFM measurements and compared to conventionally grown oxides. The authors´ studies indicate that as long as the doping level stays well below a surface concentration of 10 ²⁰ phosphorous atoms/cm³, the oxide thickness of an RTO process shows only a marginal dependence the doping level, oxidation temperature, and oxidation time. However, the oxide thickness depends strongly on the above mentioned parameters once the excess phosphorous is present in the surface region of the substrate. Explanations for this behaviour are proposed