Abstract
The mechanism of the thermal oxidation of silicon substrates was studied, based on the determination of the oxygen pressure dependence of the solubility of oxygen in SiO2 films by the use of the double oxidation method.
Silicon substrates were oxidized in a dry oxygen ambient. The results were analyzed, based on the linear-parabolic model. The activation energies were calculated to be 157 and 130 kJ/mol for the linear rate constant, kL, and the parabolic rate constant, kP, respectively. Both kL and kP were proportional to the first power of oxygen pressure, PO2.
The double oxidation method was employed for determining the oxygen pressure dependence of the solubility of oxygen into the SiO2 film, C*, the interstitial diffusivity of oxygen in the SiO2 film, D, and the rate constant of the chemical reaction at the SiO2/Si interface, k. C* was proportional to the first power of PO2 but D and k were not dependent on PO2. On the basis of this result, it was concluded that oxygen gas dissolves into the SiO2 film as O2 molecules.
The predominant mechanism of silicon oxidation was estimated to be as follows:
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oindentOxygen gas dissolves into the interstitial sites of the SiO2 film as O2 molecules. The O2 molecules diffuse toward the SiO2/Si interface through the interstitial sites. At the interface the reaction of Si+O2→SiO2 occurs.
