METHOD FOR FABRICATING POLYSILICON THIN FLIM TRANSISTOR HAVING TRENCH GATE STRUCTURE

PURPOSE: A method for fabricating dual or multiple gate polysilicon thin film transistor is provided to allow operation in high voltage, to prevent a leakage current, and to decrease device size. CONSTITUTION: A polysilicon thin film transistor is used for a pixel array switch of panel or a drive IC in an active matrix liquid crystal display(AMLCD) device or an electroluminescence(EL) display device. The fabrication begins with a forming step of at least one trench as a vertical gate region by etching an insulating substrate(10), and then a step of successively forming an oxide layer(12) and an amorphous silicon thin film is followed. Next, a step of converting the amorphous silicon thin film into a polysilicon thin film(23) is carried out, and thereto an active layer to be used as source, drain and channel regions is formed by ion implantation. After that, a gate oxide layer(24) is formed and a trench gate electrode(25) is formed on the gate oxide layer in the trench. A field oxide layer(26) is then formed, exposing the source and drain regions in the active layer. A source electrode(28a) and a drain electrode(28b) are respectively formed into the exposed source and drain regions.