This paper is concerned with the determination of the kinetic parameters and the chemical reactions that characterize the passivation of $P_b$ centers with molecular hydrogen. $P_b$ centers are paramagnetic defects at the (111) Si-${\mathrm{SiO}}_2$ interface. In this study $P_b$ centers associated with thermal oxides grown on (111) silicon substrates at 850 °C were measured with electron paramagnetic resonance. We observe that the $P_b$ resonance appears to be unaffected by subsequent in situ vacuum anneals for temperatures up to at least 850 °C.

The passivation of $P_b$ centers with ${\mathrm{H}}_2$ occurs for temperatures above approximately 220 °C; dissociation of passivated centers in vacuum occurs for temperatures in excess of 550 °C. The rate of passivation of $P_b$ centers with ${\mathrm{H}}_2$ is proportional to the ${\mathrm{H}}_2$ concentration and the density of $P_b$ centers at the interface and is characterized by the forward rate constant $k_f$. The temperature dependence of $k_f$ is observed to obey the Arrhenius equation and is characterized by an activation energy of 1.66±0.06 eV and a preexponential factor, $k_{0f}$, of ${1.94}_{\mathrm{-}1.00}^{+2.00\mathrm{}}$×${10}^{-6}$ ${\mathrm{cm}}^3$/sec. The rate equation for passivation of $P_b$ centers with ${\mathrm{H}}_2$ is consistent with a chemical process in which a hydrogen molecule reacts directly with a $P_b$ center. The rate at which this chemical reaction occurs is consistent with the diffusion of the ${\mathrm{H}}_2$ molecule among the accessible interstices of the ${\mathrm{SiO}}_2$ and the reaction site at $P_b$ centers. We also observe that the spin-lattice relaxation time, $T_1$, for $P_b$ centers at low temperatures (<100 K) increases with decreasing oxide thicknesses (<800 Å). $T_1$ also increases if the dry thermal oxides are annealed in ${\mathrm{H}}_2$ between 225 and 575 °C or cooled in Ar gas after thermal oxidation.

• Received 8 June 1988

DOI:https://doi.org/10.1103/PhysRevB.38.9657