Mechanisms of silicon oxidation at low temperatures by microwave-excited O2 gas and O2-N2 mixed gas

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Abstract
Mechanisms are discussed on the enhancement of silicon oxidation at low temperatures by microwave excitation of O2 gas and on the further increase by that of O2 ‐N2 mixed gas. The activation energy of parabolic rate constants for the oxidation by excited pure O2 gas is 1.15 eV. This value, being almost the same as that in thermal oxidation, indicates that the oxidizing species is O2 molecules. The enhancement of oxidation is interpreted as a consequence of an increase in the O2 adsorption energy on SiO2 surfaces. For the oxidation by O2 ‐N2 mixed gas, on the other hand, there exist two parallel oxidation processes: one with the excited O2 gas and the other with excited N2 gas. The activation energy for the latter oxidation process is 0.49 eV, which indicates that the oxidizing species is O atoms. We also observed an abnormally high oxidation rate in the range of small O2 /N2 ratios.