A highly reliable 0.3 μm n-channel MOSFET using poly spacers

Abstract

A reliable 0.3-μm n-channel gate-to-drain overlapped MOSFET was realized using poly spacers and demonstrated to have more than a 10-year lifetime at 3.5 V operation. This is more than two orders of magnitude longer than the conventional oxide-spacer lightly-doped-drain (LDD) devices. The large improvement is due to the unfavorable oxide field, when gate voltage (VG) is less than or equal to drain voltage (VD), for electron trapping into the gate-drain overlap region and not to the reduction of channel electric field. Under unusual operations with VG>VD the poly-spacer devices have a few times larger gate current, and thus more serious degradation, than the oxide-spacer devices. The drawbacks of the poly-space device, larger CGD and weaker gate oxide integrity can be significantly improved by a short oxidation before the poly-spacer formation. The optimum LDD dosage to avoid spacer-induced degradation is close to the highest dose before punch-through occurs. The hot-electron immunity, process simplicity and compatibility with the oxide-spacer technology make this poly-spacer device a viable approach in the deep-submicron regime