Method of making an individualization zone of an integrated circuit

A method for making an individualization zone of a microelectronic chip, said chip comprising at least:

• a first and a second level of electrical tracks,
• a level of interconnections located between the first and the second levels of electrical tracks and comprising vias intended to electrically connect electrical tracks of the first level to electrical tracks of the second level,
• the chip having at least one other zone, separate from the individualization zone, intended to form a functional zone of the chip,
• the method comprising at least the following steps carried out in the individualization zone of the chip:
• providing at least the first level of electrical tracks and at least a dielectric layer covering the first level,
• making a metal hard mask on the at least one dielectric layer having mask openings located at least in part at the electrical tracks and making the at least one dielectric layer accessible,
• etching the at least one dielectric layer through the mask openings by at least an etching based on fluorocarbon chemistry so as to form openings leading to the first level of electrical tracks,
• placing the metal hard mask in the presence of oxygen and moisture so as to form randomly distributed residues at certain openings, the openings then comprising openings with residues and openings without residues,
• filling the openings with an electrically conductive material so as to form at least the vias of the level of interconnections, said vias comprising functional vias at the openings without residues and inactive vias at the openings with residues,
• said method further comprising, prior to the formation of the residues in the individualization zone, a formation of a protective mask in the zone intended to form the functional zone.