Radiation Response in MOS Devices with High-K Gate Oxides and Metal Gates

Abstract

The effects of low and medium energy x-rays on MOS capacitors with SiO2 or HfO2 gate dielectrics and Al and TaSi gate metallization have been studied using the Monte Carlo simulator, MRED. We find good agreement between our calculations and previous results in the literature with other simulators and with experiments on devices with SiO2 gate dielectrics. There is a significant dose reduction in thin HfO2 layers exposed to 10-keV x-rays, when the HfO2 is surrounded by lower-Z materials (e.g., Si, Al). We have extended our studies to MOS capacitors with HfO2 gate dielectrics and TiN and TaN metal gates. We quantify the effects of back-end-of-line (BEOL) layers, including copper interconnect, W vias, and BPSG and SiO2 passivation layers for low and medium energy x-rays. For thick metallization stacks irradiated by 10-keV x-rays, dose enhancement or attenuation can occur, depending on material type and overlayer thicknesses. In a medium-energy x-ray environment, the dose in a HfO2 gate dielectric can be ~ 10 times higher than the dose in a SiO2 dielectric, for the same incident x-ray fluence, with increasing doses due to BEOL layers.