A manufacturing method of a semiconductor device including a step of forming a via hole in an insulation layer including an organic low dielectric film, such as MSQ, SiC, and SiCN, and then embedding a wiring material in the via hole through a barrier metal. According to this method, a plasma treatment is performed after the via hole is formed and before the barrier metal is deposited, using a He/H2 gas capable of replacing groups (methyl groups) made of organic constituents and covering the surface of the exposed organic low dielectric film (MSQ) with hydrogen, or a He gas capable decomposing the groups (methyl groups) without removing organic low dielectric molecules. As a result, the surface of the low dielectric film (MSQ) is reformed to be hydrophilic and adhesion to the barrier metal is hence improved, thereby making it possible to prevent the occurrence of separation of the barrier metal and scratches.