Parallel between Surface States at the Si–SiO2 Interface and the B2 Center in Irradiated SiO2

Abstract

The effect of annealing in nitrogen and hydrogen atmospheres on surface-state densities Nss at the Si–SiO2 interface has been measured using the linear voltage-ramp method which gives Nss vs silicon surface potential. A mercury probe was used in order to eliminate the effect of aluminum on surface-state reduction. The dependence of annealing of surface states on atmosphere and temperature closely parallels that of the B2 center in sputtered SiO2, an absorption center with maximum absorption at 5.1 eV which is observed in irradiated SiO2. In N2, temperatures between 700°C and 800°C are required to anneal completely the B2 center; Nss reaches its lowest values after annealing in N2 at 700°C. In H2, the B2 center anneals completely and Nss is reduced to its lowest values after heating at 400°C. Annealing at 600°C or 700°C in H2 increases Nss and introduces a surface-state level ∼0.1 V above the midgap energy Ei.