Hydrogenation of Defects at the Si-SiO₂ Interface

Abstract

The Si-SiO₂ interface possesses electronic defects which may be considered characteristic of the thermal oxidation process. These defects have three well-documented manifestations: (1) a broad peak in the interface-state distribution [1,2], (2) a paramagnetic center in electron spin resonance (ESR), which has been identified as trivalent silicon [3]. and (3) fixed positive space charge located in the oxide immediately adjacent to the interface. Hydrogen is generally believed to be involved in the removal of interface states, although the microscopic processes have not been established. For aluminum on SiO₂ it has been proposed that a low-temperature sinter (e.g., 450 C) releases residual hydrogen at the metal-oxide interface which subsequently diffuses to the Si-SiO₂ interface where it reacts with silicon dangling bonds and removes interface states [4,5]. However, this mechanism has been considered speculative because the chemical nature of the interface defect and its relation to interface states have not been established. Presented here are results from experimental studies of the mechanisms and effects of low-temperature processing and hydrogenation on defects at the Si-SiO₂ interface. Low-temperature anneals of the Al-SiO₂-Si system were used to compare the relative responses of the interface spin center and characteristic interface states. To more directly probe the process of hydrogenation, thermal oxides on silicon were annealed in atomic deuterium. This isotope simulates hydrogen chemistry and is readily traceable even in high background concentrations of hydrogen.