A SIMPLE OHMIC-CONTACT FORMATION TECHNOLOGY USING PHOSPHINE PLASMA TREATMENT FOR TOP-GATE AMORPHOUS-SILICON THIN-FILM TRANSISTORS

The effects of exposing patterned indium-tin-oxide (ITO) on amorphous silicon oxide (a-SiOx) to a phosphine (PH3) plasma has been investigat ed. Phosphorous atoms react with ITO to form InPOx and InP, with a muc h smaller number being deposited on a-SiOx. If amorphous silicon (a-Si ) is then deposited onto these layers by plasma enhanced chemical vapo r deposition, phosphorous atoms from the ITO are incorporated into the a-Si in the region of the ITO. This effectively dopes the a-Si to for m good ohmic contacts between the ITO and a-Si layers. In contrast, th e number of phosphorus atoms incorporated into a-Si directly above a-S iOx is too small to have an effect on the electrical properties of a-S i. The doping mechanism for the ITO and a-Si is discussed, and an expl anation given as to how these features can be used to mass produce hig h performance top-gale a-Si thin film transistors using only three pho tomask steps.