Wirings mainly containing
copper are formed on an insulating film on a substrate. Then, after forming insulating films for reservoir pattern and a barrier insulating film, an insulating film for suppressing or preventing
diffusion of
copper is formed on upper and side surfaces of the wirings, the insulating film on the substrate, and the barrier insulating film. Here, thickness of the insulating film for suppressing or preventing
diffusion of
copper at the bottom of a narrow inter-wiring space is made smaller than that on the wirings, thereby efficiently reducing wiring
capacitance of narrow-line pitches. Then, first and second low
dielectric constant insulating films are formed. Here, a
deposition rate of the first insulating film at an upper portion of the side surfaces of facing wirings is made higher than that at a lower portion thereof, thereby forming air gaps. Finally, the second insulating film is planarized by interlayer CMP.