Method of making a poly-silicon thin film transistor having lightly doped drain structure

摘要

A poly-silicon thin film transistor having LDD structure which has very low source/drain resistance is described. A TFT according to a preferred embodiment of the present invention, has, on a substrate, an active poly-silicon layer with a heavily-doped region on an outer peripheral thereof, a lightly doped region on ban inside the outer peripheral band and an un-doped region on a center part thereof. A gate insulating layer is comprised of a lower oxide layer, a nitride layer and an upper oxide layer. The lower oxide layer is formed over the whole active poly-silicon layer, but the nitride layer and the upper oxide layer are formed only on the un-doped portions of the active poly-silicon layer. A gate electrode is then formed on the upper oxide layer. A method for forming this structure is also described, which method uses a dry etch to remove the upper oxide layer and the nitride layer, but not the lower oxide layer prior to ion implantation of the active region.