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

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 (V
_G
) is less than or equal to drain voltage (V
_D
), for electron trapping into the gate-drain overlap region and not to the reduction of channel electric field. Under unusual operations with V
_G
>V
_D
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 C
_GD
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