The annealing of SiO2/(100)Si interfaces in H, at temperatures ranging from 500 to 800C, was found to introduce a considerable density of fixed positive charge. The charge was diamagnetic, and exhibited no correlation with any type of dangling bond defect at the Si surface or in the oxide. The observed charged state was attributed to H bonding to a bridging O atom at the interface (3-fold coordinated O center), which was suggested to account for a well-known oxidation-induced charge at the Si/SiO2 interface. It was pointed out that there were several features of the oxidation-induced fixed charge which matched those of H2-produced charge. Thus, an increase in the oxidation temperature to above 700C reduced the fixed charge. The fixed charge was greatest when samples were cooled rapidly. Annealing in a H-free ambient at above 600C reduced the charge density. Annealing in the presence of atomic H at 400C also resulted in a decrease in charge density. An increased availability of moisture in the ambient increased the fixed charge density. Both charges originated from diamagnetic centers. It was noted that these correlations were not definitive proof for the equivalence of oxidation- and H-induced positive charges at the Si/SiO2 interface.

V.V.Afanasev, A.Stesmans: Applied Physics Letters, 1998, 72[1], 79-81