Method of making thin film transistor with a self-aligned bottom gate

Abstract

A simple method of making a thin film transistor (TFT) on a substrate with an insulating surface layer is disclosed. A layer of dopant source layer is deposited on the insulating layer, followed by defining a gate stack consisting of a gate polysilicon, gate insulator and a protective polysilicon using the dopant source layer as an etch stop. Sidewall spacers are formed in contact with the gate stack. A TFT body polysilicon is deposited and patterned, forming thereby the source and drain regions in a self-aligned manner. By heating, the dopants from the dopant source layer are driven into the source/drain and to part of the off-set regions of the body polysilicon layer while simultaneously also doping the gate polysilicon.