A metal thin film used in fabricating a damascene interconnection of a semiconductor device which exhibits excellent high temperature fluidity during high pressure annealing, and which can fabricate an interconnection for a semiconductor device which has a low electric resistance and stable high quality is provided. Also provided is an interconnection for a semiconductor device. More specifically, a metal thin film for use as an interconnection of a semiconductor device comprising a Cu alloy containing N at a content of not less than 0.4 at % to not more than 2.0 at %; and an interconnection for a semiconductor device fabricated by forming the metal thin film on an insulator film which is formed on a semiconductor substrate and which has grooves formed therein, and filling the metal thin film in the interior of the grooves by a high pressure annealing process are provided.