The use of a material possessing a six-member borazine ring consisting of at least boron and nitrogen elements in the form of a low dielectric constant insulating film in a hard mask, a Cu diffusion barrier layer and an etching stopper which are necessary when low dielectric constant interlayer insulating films and Cu wiring in the multilayer interconnection of an LSI allows the parasitic capacity between the multilayer wirings to be suppressed and enables the ULSI to produce a high-speed operation.