Thin film transistor and manufacturing method thereof

摘要

A thin film transistor has a gate electrode formed of polysilicon on a surface of an insulating substrate or an insulating layer. The surface of the gate electrode is covered with a dielectric layer. A polysilicon layer is formed on a surface of the dielectric layer and source/drain regions are formed in this polysilicon layer. The dielectric layer covers the surface of the gate electrode and has its surface made flat. The source/drain regions are formed in the polysilicon layer on the surface of this flat dielectric layer. In another embodiment, a dielectric layer has a 2-layered structure with sidewall insulating layers located on sidewalls of a gate electrode and another insulating layer covering a surface of the gate electrode and surfaces of the sidewall insulating layers. By having larger film thickness of the dielectric layer in the vicinity of a side portion of the gate electrode than that above the gate electrode, the electric field concentration is modified in the vicinity thereof.