Methods of forming thin film transistors

Abstract

A method of forming a thin film transistor over a substrate is provided whereby at least one of the source region or the drain region is conductively doped while preventing conductivity doping of the channel region without any masking of the channel region occurring by any separate masking layer. A method includes, a) providing a substrate having a node to which electrical connection is to be made; b) providing a first electrically insulative dielectric layer over the substrate; c) providing an electrically conductive gate layer over the first dielectric layer; d) providing a second electrically insulative dielectric layer over the electrically conductive gate layer; e) providing a contact opening through the second dielectric layer, the electrically conductive gate layer and the first dielectric layer; the contact opening defining projecting sidewalls; f) providing a gate dielectric layer within the contact opening laterally inward of the projecting sidewalls; g) providing a layer of semiconductive material over the second dielectric layer and within the contact opening against the gate dielectric layer and in electrical communication with the node; the semiconductive material within the contact opening defining an elongated and outwardly extending channel region the electrical conductance of which can be modulated by means of the adjacent electrically conductive gate and gate dielectric layers; and h) conductively doping the semiconductive material layer lying outwardly of the contact opening to form one of a source region or a drain region of a thin film transistor. Thin film transistor construction are also disclosed.