Method for forming semiconductor device comprising metal oxide

A method for forming a semiconductor device comprising the steps of:

• forming a semiconductor film on an insulating surface;
• forming a gate insulating layer on said semiconductor film;
• forming a gate electrode comprising a metal on said gate insulating layer;
• oxidizing said metal of a peripheral portion of said gate electrode by anodic oxidation to form an oxide of said metal at least in the vicinity of said semiconductor film;
• forming an insulating film on said gate insulating layer over said gate electrode;
• selectively removing the insulating film and the gate insulating layer by anisotropic etching to leave a portion of the insulating film and the gate insulating layer around a side of said gate electrode;
• selectively removing the semiconductor film by etching with said gate electrode and said oxide and the remaining portion of the insulating film as a mask;
• exposing a portion of the semiconductor film provided under the remaining portion of the insulating film and a portion of the gate insulating layer provided under the remaining portion of the insulating film by etching;
• forming a conductive film on said substrate over said oxide and the exposed portion of the semiconductor film;
• and
• patterning said conductive film with a mask to form source and drain electrodes which extend on said oxide and are in contact with upper and side surfaces of the exposed portion of the semiconductor film.

A method for forming a semiconductor device comprising the steps of:

• forming a semiconductor island on an insulating surface;
• forming a gate insulating layer on said semiconductor island;
• forming a gate electrode comprising a metal on said gate insulating layer;
• oxidizing said metal of a peripheral portion of said gate electrode by anodic oxidation to form an oxide of said metal at least in the vicinity of said semiconductor island said oxide having outer edges;
• and
• adding impurity ions into portions of said semiconductor film with said gate electrode and said oxide as a mask in order to form a pair of impurity regions with opposing inner edges in said semiconductor film, wherein said inner edges of said semiconductor film are determined by said outer edges.