Two-step oxidation processes in silicon

We have studied dielectric breakdown characteristics of thin (≈10 nm) silicon dioxide films grown on silicon under the following conditions: (A) standard oxidation process with the oxide grown at 800°C; (B) annealing the oxides at 1000°C in argon for 30 min after going through step (A); (C) two-step oxidation, i.e. 800°C-4 nm followed by 1000°C anneal for 30 min in argon and a final oxidation at 800°C to grow a total of 9 nm; (D) growth of oxide at 1000°C. The results show that (B) and (C) have comparable dielectric breakdown strengths, indicating that high-temperature annealing has the same advantage as the two-step oxidation in improving the dielectric strength of silicon dioxide. High-resolution transmission electron micrographs show that the interface structures are fairly similar in all the cases indicating that the interface smoothness as observed in the transmission electron micrographs is not directly responsible for the dielectric breakdown. Our observations of the protrusions at the Si/SiO₂ interface may also possibly explain the high values of the refractive index which has earlier been attributed to a monolayer of non-stoichiometric SiO_x at the Si/SiO₂ interface.