The present invention provides a method of forming a diffusion barrier layer comprising a TaSiN layer. The method includes depositing a TaN layer into a via hole which penetrates an insulation layer exposing a first metal line layer, and transforming the TaN layer into a TaSiN layer using a radio frequency (RF) power and a (remote) plasma using SiH4 gas. Transforming the TaN layer into a TaSiN layer may include: loading a structure including the TaN layer into a plasma reaction chamber; injecting SiH4 gas into the plasma reaction chamber; and forming the TaSiN layer by reacting Si— or Si atom-containing species with the TaN layer.