Abstract: A copper layer on a substrate has a copper seed layer and an interface. The copper seed layer contains insoluble substances that are insoluble with copper. The interface is formed between the copper seed layer and the substrate. The copper layer replaces a conventional barrier and has significantly improved thermal stability to obtain some properties such as a fine microstructure, high thermal stability and an excellent low electrical resistivity. The copper seed layer is formed by a sputtering process in a vacuum and clean atmosphere with an operational gas of argon or a mixture of argon and a trace-amount of nitrogen. The interface is formed when the copper layer on the substrate are annealed. The insoluble substances in the copper seed layer are in a range of 0.5 to 3.5 atom % and are high-temperature metals and high-temperature metal nitrides with the nitrides being than 2.0 atom %.