Comparison of drain structures in n-channel MOSFET's

Practical limitations in channel lengths for n-channel MOSFET'S under 5-V operation are discussed for conventional arsenic-drain, phosphorus-drain, phosphorus-arsenic double diffused drain (DDD), and lightly doped drain (LDD) structures. Process parameter dependence of device characteristics and optimal process conditions are also evaluated for each drain structure. It is clarified that the minimum usable channel length is about 0.7-µm, which is realized by the DDD and LDD devices. In these devices, the hot-carrier-induced device degradation is no longer a major restriction on minimum channel length, but the short-channel effect and the parasitic bipolar breakdown are dominant restrictions. The phosphorus drain with a shallow junction formed by rapid thermal annealing can expand the arsenic drain limitation.