Method of forming a buried plug and an interconnection

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

• forming an insulation film over a semiconductor substrate;
• providing a photo-resist pattern over said insulation film;
• carrying out an anisotropic etching to form a contact hole in said insulation film so that a part of said semiconductor substrate is shown through said contact hole;
• forming a base layer comprising first materials not only over a top surface of said insulation film but also on vertical side walls of said contact hole;
• in a single step depositing a conductive film, of a second material not including any of said first materials, in direct contact with and over said base layer so that said conductive film extends not only over said base layer extending over said insulation film but also within said contact hole, wherein said conductive film over said top surface of said insulation film has a first thickness which is thicker than a second thickness;
• subjecting a top surface of the conductive film to a chemical and mechanical polishing to planarize said top surface of sad conductive film so that the conductive film over said insulation film has said second thickness whereby an interconnection layer is unitarily formed with a conductive plug of said conductive film buried within said contact hole without any interface between said interconnection layer and said conductive plug;
• and
• patterning said conductive film over said insulation film to form at least an interconnection over said insulation film so that said interconnection is united with said conductive plug.