A semiconductor device has interconnects protected with an alloy film
having a minimum thickness necessary for producing the effect of
preventing diffusion of oxygen, copper, etc., formed more uniformly over
an entire surface of a substrate with less dependency to the interconnect
pattern of the substrate. The semiconductor device includes, embedded
interconnects, formed by filling an interconnect material into
interconnect recesses formed in an electric insulator on a substrate, and
an alloy film, containing 1 to 9 atomic % of tungsten or molybdenum and 3
to 12 atomic % of phosphorus or boron, formed by electroless plating on
at least part of the embedded interconnects.