A Unique Approach to Generate Self-Aligned T-Gate Transistors in Counter-Doped Poly-Si With High Etching Selectivity and Isotropy

A unique approach for fabricating poly-Si thin-film transistors (TFTs) with self-aligned T-shaped gate (T-gate) structure is reported. A counter-doped poly-Si process comprises an in-situ doped n(+) poly-Si deposition followed by a subsequentshallow implantation of BF2+. Both high etching isotropy in n(+) poly-Si and high etching selectivity between n(+) poly-Si and B-doped poly-Si in a Cl-2-based plasma process are the key enablers for the fabrication of our T-gate structures. Thanks to good control in the shape and deformation of our T-gate structure, sidewall air-gap spacers in combination with self-aligned Ni silicided gate and source/drain were established. High-performance sub-micron poly-Si TFTs are evidenced by superior transfer characteristics measured on TFTs with effective gate length of 0.15 mu m . The unique T-gate structure provides an effective way for possible production of poly-Si radio-frequency TFTs viable for emerging new applications.