Thin-film transistor manufacture.

摘要

Source (51) and drain (52) of a thin-film transistor (TFT) are formed from a conductive layer (5) using a photolithographic step (Figure 3) in which the gate (4) serves as a photomask. In accordance with the invention the insulated gate structure (3,4) is formed at the upper face of the channel-forming semiconductor film (2), i.e. remote from the transparent substrate (1). The semiconductor film (2) may be annealed to high-mobility polycrystalline material before depositing the gate structure (3,4) and the overlying conductive layer (5). In this way, high speed TFTs can be formed due to a combination of low gate-to-drain and gate-to-source capacitances and the provision of the transistor channel in the high quality semiconductor material adjacent to the upper face of the film (2). Preferably ultra-violet radiation (20: Figure 1) is used for the annealing with an absorption depth less than the thickness of the film (2) so that the film-substrate interface is not heated which otherwise may weaken the adhesion of the film (2) to the substrate (1). By using an angled exposure in a photolithographic and etching step with the gate (4) as a shadow photomask, a low-doped drain part can be defined from a conductive layer (5) comprising highly-doped material on low-doped material. This low-doped drain part reduces the effect of high drain bias in operation of the TFT.