We investigated the possibility of applying an ALD method to form a Cu diffusion barrier layer of MnOx in an attempt to develop a deposition process which would not be influenced by absorbed water in a substrate. The MnOx formed by ALD using (EtCp)2Mn and H2O had the following features. (1) Capability of thickness control of the MnO x layer by changing the ALD cycle number. (2) Capability of the ALD-MnOx formation on low-k dielectrics by surface modification. (3) Good adhesion of the Cu/ALD-MnOx/SiOCH structure showing a fracture toughness of 0.3 MPa·m1/2. (4) Good diffusion barrier property for the thickness of over 1 nm. (5) Minimizing via resistance increase accompanied by the formation of MnOx on Cu.