Post-Gate Plasma and Sputter Process Effects on the Radiation Hardness of Metal Gate CMOS Integrated Circuits

The compatibility of several post-gate plasma and sputtering processes with radiation-hardened CMOS processing has been investigated. Plasma etching, plasma ashing, RF sputter etching, and DC magnetron sputtering were found to cause little effect on the threshold voltage shifts observed on CMOS inverters under gamma irradiation. However, passivation of CMOS integrated circuits with reactive-plasma-deposited SiNx films causes severe postirradiation threshold shifts. The dependence of these threshold shifts on SiNx thickness, deposition parameters, and postdeposition anneals has been characterized. Intervening CVD films between the metal layer and the SiNX have a significant effect and in some cases reduce the observed threshold shifts considerably. The observed threshold shifts do not appear to be related to the stress of the SiNx films.