Method of making MES field effect transistor using III-V compound semiconductor

A method of making a MES field effect transistor comprising the steps of:

• depositing a first insulating film on a surface of a compound semiconductor substrate;
• depositing a second insulating film on said first insulating film, said second insulating film being comprised of a silicon dioxide film having a thickness of about 1000 A;
• selectively removing said second insulating film by means of lithography techniques except a portion corresponding to a channel region;
• coating said first insulating film with a resist layer;
• patterning said resist layer so as to define intended source and drain regions with both the residual resist layer and said selectively removed second insulating film;
• subjecting said semiconductor substrate to an ion implantation using different acceleration voltages in the presence of both said first and second insulating films to provide source and drain regions and said channel region;
• subjecting said semiconductor substrate to a heat-treatment to activate said ion-implanted regions;
• successively removing said second insulating film and said first insulating film formed on said channel region;
• forming a Schottky gate electrode on said channel region;
• selectively removing said first insulating film from the substrate surface of said source and drain regions;
• and
• forming an electrode on said source and drain regions.