Degradation of Radiation Hardness in CMOS Integrated Circuits Passivated with Plasma-Deposited Silicon Nitride

The sensitivity of metal gate CMOS integrated circuits to ionizing radiation is shown to be affected by the final passivation employed. Specifically, plasma-deposited silicon nitride produces an unexpected degradation in radiation hardness due to the generation of charged surface states at the Si-SiO2 interface. The relationship between the silicon nitride deposition temperature and device threshold voltage shifts is explored as well as the effects of post-passivation anneals. These results indicate that several mechanisms are responsible for the hardness degradation, with effects due to hydrogen diffusion appearing to be of central importance.