KINETICS AND MECHANISM OF THERMAL OXIDATION OF SILICON WITH SPECIAL EMPHASIS ON IMPURITY EFFECTS

Thermal oxidation of silicon was investigated under a variety of conditions. The oxidation follows a combination of linear and parabolic rate lows; the rate constants obey the Arrhenius relationship. Under very clean conditions (dry O2, r.f. heating) the rate constants differ substantially from the values obtained by oxidation in resistance heated furnaces. In comparison with oxidation in dry O2, oxidation in water vapor is characterized by larger pre-exponential terms and activation energies in the linear regime, but both are smaller in the parabolic regime. Sodium, that was deliberately introduced during oxidation, increased the parabolic and linear pre-exponential factors and activation energies. It is proposed that oxide growth takes place via an interstitialcy diffusion mechanism in which both ionic and molecular oxygen participate. The surface reaction in the linear growth regime and the diffusion mechanism, as well as the concentration of the diffusing species in the parabolic regime, are greatly affected by sodium (or similar impurities) and water vapor in the oxidizing ambient. MOS capacitance measurements of Na-doped oxides showed that most of the sodium is inactive from the viewpoint of both surface state density and ion migration under high field at elevated temperature. © 1969.