A new LDD transistor with inverse-T gate structure

Abstract

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--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 YLSI applications.

Effects of a lightly-doped-drain (LDD) implantation condition on the device characteristics of polycrystalline-Si thin-film transistors

“…Figure 5 shows the lateral dopant distribution profiles around the drain region near the substrate surface for the LDD TFTs with various LDD implantation energies at a LDD implantation dose of 3 × 10 13 cm −2 , respectively. It is found that a larger LDD implantation energy results in a more gradual and more widely distributed dopant profile, which is helpful to the formation of a gate-overlapped drain structure [10,11] imp. dose= 3E13 that can effectively reduce the off-state leakage current.…”