A new LDD transistor with inverse-T gate structure

A new submicrometer inverse-T lightly doped drain (ITLDD) transistor structure for alleviating hot-electron effects is demonstrated. A thin extension of the polysilicon gate under the oxide sidewall spacer is formed, giving the gate cross section the appearance of an inverted letter T. Due to the unique self-aligned n+ T-to-gate feature facilitated by the conducting polysilicon extension, the "spacer-induced degradation" existing in a conventional LDD transistor is eliminated in ITLDD devices. This allows the use of low n- LDD doses for optimum channel electric field reduction and minimum post-implant drive-in for future VLSI compatibility. Submicrometer ITLDD transistors with good transconductance and hot-electron reliability have been achieved. The new ITLDD transistor offers a promising device structure for future VLSI applications.