A method is provided for forming spacers of a gate of a field effect transistor, the gate including flanks and a top and being located above a layer of a semiconductor material, the method including a step of forming a dielectric layer covering the gate; after the step of forming, at least one step of modifying the dielectric layer by putting the dielectric layer into presence of a plasma creating a bombarding of light ions; and at least one step of removing the modified dielectric layer including a dry etching performed by putting the modified dielectric layer into presence of a gaseous mixture including at least one first component with a hydrofluoric acid base that transforms the modified dielectric layer into non-volatile residue, and removing the non-volatile residue via a wet clean performed after the dry etching or a thermal annealing of sublimation performed after or during the dry etching.