A proposed model for positive charge in SiO2 thin films. Over-coordinated oxygen centers

We find that annealing oxides in a H₂ containing ambient creates positive charge in the dielectric of Si/SiO₂/Si structures. The H-induced positive oxide charge is shown to be very different from radiation-induced oxygen vacancy hole traps (E´ centers) in SiO₂. We find that three factors strongly influence the ability to create H-induced positive charge: temperature, hydrogen concentration in the ambient, and the density of hydrogen cracking centers. We suggest that over-coordinated O centers are responsible for this charge. The proposed over-coordinated oxygen centers may also account for the equivocal nature of several forms of positive charge that have escaped detection by electron paramagnetic resonance, such as the fixed oxide charge that forms during the thermal oxidation of Si