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: (1) trapping of electrons at coulombic centers in the bulk oxide and (2) 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 post-anneal neutral electron traps and the failure of the forming gas anneal to fully restore the pre-irradiation hydrogen-transport properties of the oxide