US Patent 7229863 Method for fabricating thin film transistors

A method for fabricating a thin film transistor is provided. First, a gate is formed on a substrate. A gate-insulating layer is formed to cover the gate. A patterned semiconductor layer is formed on the gate-insulating layer. A first and a second conductive layer are formed on the patterned semiconductor layer in sequence. The second conductive layer is patterned such that each side of thereof above the gate has a taper profile and the first conductive layer is exposed. A first plasma process is performed to transform the surface and the taper profile of the second conductive layer into a first protection layer. The first conductive layer not covered by the first protection layer and the second conductive layer is removed to form a source/drain. The source/drain is with fine dimensions and the diffusion of metallic ions from the second conductive layer to the patterned semiconductor layer can be avoided.