The invention relates to a method whereby a laser beam having a pre-determined wavelength is used to etch a zone (16) of a film (14) of a first material, said zone (16) being deposited on the surface of at least two materials (10, 12). The method consists in: depositing a film (18) of a third material on the film (14) of first material, the first and third materials having a chemical affinity during the application of the laser beam that is greater than the chemical affinity during the application between the first material and each of said at least two second materials; and applying the laser beam to a zone of a free surface of the film (18) of third material vertically above the zone (16) of the film (14) of first material, with a fluence of the laser beam causing the separation of said zone (16).