Combined effect of X-irradiation and forming gas anneal on the hot-carrier response of MOS oxides

Process-radiation-induced defects and hot-carrier instability in n-channel transistors subjected to simulated X-ray lithography have been studied. Using optically assisted electron injection (photoinjection), two specific instability mechanisms were investigated. These mechanisms are trapping of electrons at Coulombic centers in the bulk oxide and depassivation/passivation of interface traps by hydrogen originating in the bulk oxide. Devices treated with a standard forming gas anneal after X-irradiation show residual, but minor, susceptibility to hot-carrier-induced instability via both these mechanisms. These results can be explained by the presence of postanneal neutral electron traps and the failure of the forming gas anneal to fully restore the preirradiation hydrogen-transport properties of the oxide.>