Radiation Effects in LDD MOS Devices

The purpose of this work is to investigate the response of lightly doped drain (LDD) n-channel transistors to ionizing radiation. Transistors were fabricated with conventional (non-LDD) and lightly doped drain (LDD) structures using both standard (non-hardened) and radiation hardened gate oxides. Characterization of the transistors began with a correlation of the total-dose effects due to 10 keV x-rays and Co-60 gamma rays. We find that for the gate oxides and transistor structures investigated in this work, 10 keV x-rays produce more fixed-charge build-up in the gate oxide, and more interface charge than do Co-60 gamma rays. We have determined that the radiation response of LDD transistors is similar to that of conventional (non-LDD) transistors. In addition, both standard and radiation-hardened transistors subjected to hot carrier stress before irradiation show a similar radiation response. After exposure to 1.0 × 106 rads(Si), non-hardened transistors show increased susceptibility to hot-carrier degradation, while the radiation-hardened transistors exhibit similar hot-carrier degradation to non-irradiated devices. We have demonstrated a fully-integrated radiation hardened process that is solid to 1.0 × 106 rads(Si), and shows promise for achieving 1.0 × 107 rad(Si) total-dose capability.