Transportation of carriers in silicon implanted SiO2 films during ionizing radiation

Silicon ion implantation has been proved to be an effective method for total-dose hardening of SiO2 in MOS devices such as buried oxides in SOI devices, while the mechanisms are still in discussion. In this work, behavior of 10 keV X-ray induced carriers in silicon implanted thermal SiO2 was investigated by comparing with Ar implanted SiO2. Photoluminescence (PL) spectroscopy and TRIM calculation were used to characterize the defects of the ion implanted SiO2 films. Metal–Oxide–Semiconductor (MOS) structures were fabricated for electrical characterization of the oxides. Positive or negative gate bias was applied during the irradiation to control the separation and transportation of radiation induced electrons and holes. Flatband voltage shifts and are extracted from high frequency capacitance–voltage (C–V) measurement results which are taken prior to and after certain total dose irradiation. The experiment result shows that both Ar and Si implantation and followed anneal could eliminate the net positive charge in SiO2 irradiated by X-ray. But different with Ar implanted oxide, in Si implanted oxide, the reduction of positive charge is highly dependent on the implanted Si ion fluence, and is well consistent with silicon nanoclusters evolvement tendency. From these results we conclude that along with increased electron trapping at the nanostructures which is suggested by previous studies, enhanced hole trapping and recombination caused by implantation induced vacancy defects are critical mechanism of reduced total ionizing dose effects on Si implanted oxides.