An electron spin resonance (ESR) study has been carried out of point defects generated in standard thermal ${\mathrm{SiO}}_2$ on (100) Si during vacuum annealing in the temperature range $T_{\mathrm{an}}=950\mathrm{}–1250°\mathrm{C},$ including the predominant exclusive S center in addition to the familiar $E_{\gamma }^{\prime },$ $E_{\delta }^{\prime },$ and EX defects. The latter only appear after 10-eV optical excitation. The S and $E_{\gamma }^{\prime }$ density is found to increase monotonically with $T_{\mathrm{an}},$ while EX and $E_{\delta }^{\prime }$ detectivity fades for $T_{\mathrm{an}}>~1050$ and 1200 °C, respectively. Over broad $T_{\mathrm{an}}$ ranges, the generation of all three defects S, $E_{\gamma }^{\prime },$ and $E_{\delta }^{\prime }$ appears thermally activated (Arrhenius type) with a common activation energy $E_a\approx 1.6\mathrm{eV}.$ Large defect densities may be reached, i.e., [S] up to $\sim 1\times {10}^{15}{\mathrm{cm}}^{\mathrm{-}2}$ for $T_{\mathrm{an}}=1250\mathrm{}°\mathrm{C},$ typically one order of magnitude larger than $\left[E_{\gamma }^{\prime }\right].$ With a view to identification, the S-center ESR characteristics have been mapped in detail. Its susceptibility is found nearly paramagnetic—Curie-Weiss type with critical temperature $T_c=1.3\mathrm{}\pm 0.4\mathrm{K},$ indicative of a weak ferromagnetic coupling; the defects appear clustered. Oxide etch-back experiments reveal that during degradation the oxide undergoes significant modification, dependent on depth into the oxide film. As to defect distribution, for $T_{\mathrm{an}}=1200\mathrm{}°\mathrm{C},$ the etch-back experiments show the S centers to predominantly occur near the oxide borders, with a sharp pileup within ∼40 Å of the ${\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}\mathrm{O}}_2$ interface, and a more stretched out one (∼150 Å) towards the top surface; S and $E_{\gamma }^{\prime }$ centers generally occur in anticorrelation. The S defects are susceptible to passivation in molecular ${\mathrm{H}}_2.$ From the salient ESR properties, the S center is suggested to be of the type ${\mathrm{Si}}_n{\mathrm{O}}_{3-n}\equiv \mathrm{Si}\cdot \hspace{0.5em}\mathrm{}(n=1,2\mathrm{}).$ Though tentative, the observed weak hyperfine structure may be compatible with either the single $n=1\mathrm{}$ defect or an overlap of both the $n=1,$2 types, the defect system exhibiting substantial randomness-induced variation in defect morphology. Based on the known interfacial ${\mathrm{SiO}}_2$ reduction process, the thermal degradation of the oxide as a whole is interpreted as effectuated by interface-released SiO.

• Received 27 July 2001

DOI:https://doi.org/10.1103/PhysRevB.66.045307