Dissociation kinetics of hydrogen-passivated (111) Si-SiO2interface defects

This paper is concerned with the chemical kinetics of the transformation of hydrogen-passivated interface defects (H${\mathit{P}}_{\mathit{b}}$ centers) into paramagnetic ${\mathit{P}}_{\mathit{b}}$ centers (⋅Si?${\mathrm{Si}}_3$) at the (111) Si-${\mathrm{SiO}}_2$ interface under vacuum thermal annealing. Float-zone (111) silicon substrates were oxidized in dry oxygen at 750 °C to a thickness of 500 Å, passivated with ${\mathrm{H}}_2$ (${\mathrm{D}}_2$) at 300 °C for 3 h (4 h), and then vacuum thermal annealed at temperatures ranging from 500 to 595 °C. The results of this analysis indicate that the kinetic process is described by a first-order rate equation d[H${\mathit{P}}_{\mathit{b}}$]/dt=-${\mathit{k}}_{\mathit{d}}$[H${\mathit{P}}_{\mathit{b}}$] where ${\mathit{k}}_{\mathit{d}}$=${\mathit{k}}_{\mathit{d}0}$exp(-${\mathit{E}}_{\mathit{d}}$/kT). An activation energy of 2.56±0.06 eV with a preexponential factor ${\mathit{k}}_{\mathit{d}0}$ of approximately 1.2×${10}^{12}$ ${\sec }^{\mathrm{-}1}$ was obtained. The reaction rate is reduced if the samples are passivated with deuterium instead of hydrogen. These results suggest that the chemical process is due to the thermal decomposition of the H${\mathit{P}}_{\mathit{b}}$ center into ${\mathit{P}}_{\mathit{b}}$ centers and atomic hydrogen. Although the activation energy for the diffusion of interstitial oxygen in silicon is also 2.56 eV, a rate-limiting step involving this mechanism is inconsistent with the hydrogen isotope effect as well as other considerations. Comparison of the activation energies for the ${\mathrm{H}}_2$ passivation of the ${\mathit{P}}_{\mathit{b}}$ center and dissociation of the H${\mathit{P}}_{\mathit{b}}$ center are shown to be chemically and energetically equivalent to the dissociation of the ${\mathrm{H}}_2$ molecule as originally indicated by Myers and Richards. Thus, the reverse passivation reaction, H+H${\mathit{P}}_{\mathit{b}}$→${\mathit{P}}_{\mathit{b}}$+${\mathrm{H}}_2$, and the reverse dissociation reaction, H+${\mathit{P}}_{\mathit{b}}$→H${\mathit{P}}_{\mathit{b}}$, are exo- thermic reactions that proceed with very little thermal activation in the presence of atomic hydrogen.