Method for fabricating trench metal-oxide-semiconductor field effect transistor

A method for fabricating a trench metal-oxide-semiconductor field effect transistor is disclosed. The method comprises steps of providing a substrate with an epitaxy layer thereon and etching the epitaxy layer to form a trench structure; forming a gate oxide layer on the surface of the epitaxy layer and the inner sidewalls of the trench structure and depositing a polysilicon layer to fill the trench structure; introducing a nitrogen gas and performing a driving-in procedure to form a body structure; performing an implantation procedure to form a source layer; forming a dielectric layer on the trench structure and the source layer; etching the dielectric layer and the source layer to define a source structure and form a contact region; filling the contact region with a contact structure layer; and forming a conductive metal layer on the contact structure layer and the dielectric layer.