Total dose radiation hardening of MOS transistors by fluorine implantation

Abstract

Total ionizing dose effects are predominantly due to hole traps at the Si/SiO2 interface at the shallow trench isolation (STI) and buried oxide. Here we show that Fluorine ion implantation is capable to fully passivate those traps such that negligible threshold shift is discernible in NMOS transistors radiated up to a maximum dose of 1MRad (Si). H-gate transistor were designed and fabricated using thin gate oxide, source drain pull back and ion implanted Fluorine to address radiation effects in the gate oxide, STI and buried oxides respectively. The transistors hardness was tested using gamma radiation from a Co60 source. Transistors without fluorine show a threshold voltage shifts of up to 350mV. Fluorine doped transistors show negligible threshold shifts up to the maximum dose.