Silicon Oxidation Studies: The Role of H2O

The thermal oxidation of Si using H(2)zO=O-2 and H2O=N-2 ambients has been studied with an automated ellipsometer which can observe the oxidation in situ. The oxidations were carried out in the temperature range of 780 degrees 980 degrees C on < 100 > oriented single crystal Si. The resulting SiO2 film growth data was analyzed according to a linear-parabolic oxidation model. The parabolic rate constant was found to increase abruptly with small additions of H2O to O-2 while the linear rate constant increased gradually over the range of added H2O (0- 2000 ppm). The over-all increase in the rate of oxidation due to H2O in O-2 was found to be greater than predicted based on the independent diffusion and reaction of O-2 and H2O related oxidant species. These effects of H(2)oO were found to be reversible. Therefore, the kinetic role of HO H2O on the oxidation of silicon is essentially twofold. The H2O acts both as an additional source of oxidaht and as an accelerator for the oxidation process involving O-2. It is postulated that this latter effect occurs because the H2O modifies the SiO2 network thereby enhancing diffusion of the primary oxidant through the SiO2 film.