Short-Channel Poly-Si Thin-Film Transistors with Ultrathin Channel and Self-Aligned Tungsten-Clad Source/Drain

A short-channel polycrystalline silicon (poly-Si) thin-film transistor (W/ L = 10 μm/3 μm) with an ultrathin channel (30 nm) and self-aligned tungsten-clad source/drain structure is demonstrated. With WF₆ and SiH₄ gas flow ratio of 40/12, selectively deposited tungsten film over 100 nm thick can be easily grown on source/drain regions. As a result, the parasitic source/drain resistance is greatly reduced, leading to improvement of device driving ability. Because tungsten deposition can be carried out at a low processing temperature of 300°C, the proposed simple structure is compatible with conventional top-gate structure and can be readily applied to low-temperature poly-Si fabrication.