Secondary ion mass spectrometry characterization of D₂O and H₂ ¹⁸O steam oxidation of silicon

Abstract

Silicon wafers were steam oxidized at temperatures of 550–1000°C and pressures of 0.05–8 atm with H₂ ¹⁶O, H₂ ¹⁸O, and D₂ ¹⁶O. Deuterium (D) and¹⁸O profiles in 100–200 nm thick oxide films were measured with Cs⁺ beam secondary ion mass spectroscopy (SIMS). The use of D and¹⁸O isotopes enabled analysis of these elements without interference from the sputtering ambient. Peaks in the D profiles near the interface are due predominantly to abrupt changes in the ion yield and charging conditions as the interface is approached. Although the D concentration is nearly constant at ∼ 1 × 10²⁰ cm⁻³ for 700–1000°C oxidations, it rises to a non-equilibrium value of 6 × 10²⁰ cm⁻³ at 600°C. Analysis of steam indiffusions below 800°C indicates that the OD concentration is proportional to the (steam pressure)^1/2, in agreement with earlier results on as-oxidized wet thermal oxides. The results of sequential isotope oxidations indicate that there is rapid exchange ofboth the hydrogen and oxygen species during transport of “water” to the SiO₂. Si interface. We examine these results in terms of the concentrations of the interacting species in the oxide films, and our results are compared to similar reported studies.