Method for making a thin film transistor

A method for making a thin film transistor comprising the steps of:

• forming a thin film semiconductor layer entirely on a substrate,
• etching said semiconductor layer into a predetermined semiconductor pattern, so as to form an etched semiconductor layer
• depositing, in succession, a gate insulation film and a gate electrode film entirely over said etched semiconductor layer,
• applying an alignment mask over said gate electrode film corresponding to said predetermined semiconductor pattern, said alignment mask forming a gate pattern for both said gate electrode film and said gate insulation film,
• etching said gate electrode and gate insulation films to form gate insulation and gate electrode films having self-aligned structures in said gate pattern over said semiconductor layer in said semiconductor pattern, and to form exposed portions of said semiconductor layer,
• removing said alignment mask,
• depositing a metal layer over said substrate, said semiconductor layer, said gate electrode film, and said gate insulation film,
• diffusing metal atoms from said metal layer into said exposed portions of said semiconductor layer, thereby forming a first and a second low resistance area,
• forming a source electrode by etching and deposition on said substrate, said source electrode contacting said first low resistance portion, and
• forming a drain electrode by etching and deposition on said substrate, said drain electrode contacting said second low resistance portion.