Method for increasing the surface roughness of a metal layer

A method for increasing a surface roughness of a metal layer based on titanium, tantalum, tungsten, gold, nickel and/or aluminum, comprising:

• fixing fluorine or chlorine on the surface of the metal layer, by exposing the metal layer to a plasma formed from a reactive gas containing fluorine or chlorine;
• after fixing fluorine or chlorine on the surface of the metal layer, exposing the surface of the metal layer to a humid environment to produce an acid, by reaction of hydrogen from the humid environment with the fluorine or the chlorine fixed on the surface of the metal layer, the acid reacting with the metal to form residues, the whole of the residues forming a pattern on the surface of the metal layer, and
• after forming the residues, etching the metal layer through the residues, so as to transfer the pattern into the metal layer.