Charge states of the reactants in the hydrogen passivation of interstitial iron in P-type crystalline silicon

Abstract

Significant reductions in interstitial iron (Fe<inf>i</inf>) concentrations occur during annealing Fe-containing silicon wafers with silicon nitride films in the temperature range of 250°C-700°C. The silicon nitride films are known to release hydrogen during the annealing step. However, in co-annealed samples with silicon oxide films, which are hydrogen-lean, changes in the Fe<inf>i</inf> concentrations were much less significant. The precipitation of Fe<inf>i</inf> is ruled out as a possible explanation for the significant reductions. The hydrogen passivation of Fe<inf>i</inf>, which is the complexing of monatomic H and isolated Fe<inf>i</inf> forming a recombination-inactive hydride, is proposed as the most probable model to explain the reductions. Under the assumption that the reduction is caused by the hydrogenation of Fe<inf>i</inf>, the reactants' charge states in the hydrogenation reaction are determined by two independent approaches. In the first approach, illumination is found to have a small but detectible impact on the reaction kinetics in the lower temperature range. The dominating reactants' charge states are concluded to be Fe0 + H+ as revealed by modelling the injection-dependent charge states of isolated Fe<inf>i</inf> and monatomic H. In the second approach, the reaction kinetics are fitted with the Arrhenius equation over a large temperature range of 250°C-700°C. A reasonable fit is only obtained when assuming the reacting charge states are Fe0+H+. This supports the conclusion on the reacting charge states and also gives a value of the activation energy of hydrogenation in the 0.7-0.8eV range.