Gamma and vacuum ultraviolet irradiations of ion implanted SiO2 for MOS dielectrics

Electrical measurements are described for grown silicon dioxide thin films irradiated by gamma rays, X-rays and broadband VUV light. The dependence of radiation sensitivity on processing variations, including annealing temperature, is compared for unimplanted SiO2 and SiO2 implanted with aluminum, argon, xenon and cerium. The flatband voltage shift is suppressed under positive irradiation bias by each of these ions. This suggests that the implantation of ions at energies of several kilovolts, with fluences of 100 trillion to 1,000 trillion per sq cm, improves hardness by the production of similar distributions of electron traps with densities of the order of 1 trillion traps per sq cm by lattice damage, and not by the direct combination of the ion with intrinsic or radiation-induced hole traps. It is confirmed that ion implantation into the dielectric is a versatile method for producing radiation tolerance under positive bias in silicon dioxide.