Continuing miniturization efforts in silicon device technology require an increase in the energy barrier at the SiO2-Si interface which can be influenced by incorporation of impurities. In our experiments the thermal behavior of conventionally (C) and ultra-cleanly (U) prepared SiO2 (12 ≦ d ≦ 23 A ̊) on Si(100) was studied by Angle-Resolved Ultraviolet Photoelectron Spectroscopy (ARUPS). Contrary to conventional oxugen atmospheres applied mostly by the semiconductor industry, the ultra-clean gas used in our dry oxidation furnace contains only traces of H2, N2 and water vapor. The comparison of the temperature dependence reveals that the critical temperature Tc for the decomposition reaction is higher in the case of C-oxide than for the corresponding U-oxide. Also, only for the C-oxide an additional peak in the UPS spectra can be distinguished indicating that impurities incorporated during the conventional oxidation attach to dangling bonds of interface Si atoms. We speculate that the impurities stabilize the overlayer against thermal degradation by decreasing the misfit stress at the SiO2-Si interface.
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