A method for bonding a first copper element onto a second copper element including forming a crystalline copper layer enriched in oxygen on each of surfaces of each of the first and second elements through which the elements will be in contact, the total thickness of both layers being less than 6 nm, which includes: a) polishing the surfaces so as to obtain a roughness of less than 1 nm RMS, and hydrophilic surfaces, b) cleaning the surfaces to suppress presence of particles due to the polishing and the major portion of corrosion inhibitors, and c) putting both crystalline copper layer enriched in oxygen in contact with each other.