Semiconductor device and a fabrication process thereof

A method of fabricating a semiconductor device having a contact structure comprising a conductor body, an insulation film covering said conductor body, and a contact plug penetrating through said insulation film and electrically connected to said conductor body, said method comprising the steps of:

• forming a contact hole in said insulation film to extend therethrough and to expose said conductor body at a bottom part of said contact hole;
• forming a barrier metal film of tungsten nitride over said bottom part and a sidewall surface of said contact hole with a conformal shape to said bottom part and said sidewall surface of said contact hole;
• forming a tungsten layer to fill said contact hole via said barrier metal film;
• and
• forming a tungsten plug in said contact hole by said tungsten layer by polishing away a part of said tungsten film over said insulation film until a surface of said insulation film is exposed,
• wherein there is conducted a step of cleaning a surface of said conductor body prior to said forming step of said barrier metal film,
• said barrier metal film is formed such that a nitrogen concentration therein decreases from a first side thereof contacting with said bottom surface and said sidewall surface of said contact hole to a second side contacting with said tungsten plug, and
• said barrier metal film causes transition to said tungsten plug continuously at said second side.