A method for forming spacers (152a, 152b) of a field effect transistor gate, with the gate being located above an active layer made of a semiconductor material, comprising a step of forming a nitride-based layer overlying the gate of said transistor, with the method being characterized in that it comprises, after the step of forming the nitride-based layer: - at least a step of modifying the nitride-based layer by contacting the nitride-based layer with plasma wherein CxHy is introduced where x is the proportion of carbon and y is the proportion of hydrogen ions, and comprising ions heavier than hydrogen; with the conditions of plasma, more particularly the concentration of CxHy, the ion energy and the main implantation direction being so chosen that: ∘ plasma creates an anisotropic bombardment with hydrogen-based ions (H, H +, H 2 +, H 3 + etc.) from CxHy, with the bombardment being anisotropic in a direction parallel to flanks of the gate and so as to modify an upper portion of the thickness of the nitride-based layer at the level of the flanks of the gate only, while keeping non-modified portions (152a, 152b) of the nitride-based layer covering the flanks of the gate. ∘ plasma chemical species containing carbon from CxHy form a carbon film specifically on surfaces parallel to the direction of the bombardment; ∘ plasma creates a bombardment with ions heavier than hydrogen which prevents said carbon-containing plasma chemical species from CxHy from forming a carbon film, more particularly on the surfaces of the nitride-based layer which are perpendicular to the direction of the bombardment. - at least a step of removing the nitride-based modified layer using a selective etching of the nitride-based modified layer relative to non-modified portions (152a, 152b) of the nitride-based layer. - at least a step of modifying the nitride-based layer by contacting the nitride-based layer with plasma wherein CxHy is introduced where x is the proportion of carbon and y is the proportion of hydrogen ions, and comprising ions heavier than hydrogen; with the conditions of plasma, more particularly the concentration of CxHy, the ion energy and the main implantation direction being so chosen that: ∘ plasma creates an anisotropic bombardment with hydrogen-based ions (H, H +, H 2 +, H 3 + etc.) from CxHy, with the bombardment being anisotropic in a direction parallel to flanks of the gate and so as to modify an upper portion of the thickness of the nitride-based layer at the level of the flanks of the gate only, while keeping non-modified portions (152a, 152b) of the nitride-based layer covering the flanks of the gate. ∘ plasma chemical species containing carbon from CxHy form a carbon film specifically on surfaces parallel to the direction of the bombardment; ∘ plasma creates a bombardment with ions heavier than hydrogen which prevents said carbon-containing plasma chemical species from CxHy from forming a carbon film, more particularly on the surfaces of the nitride-based layer which are perpendicular to the direction of the bombardment. ∘ plasma creates an anisotropic bombardment with hydrogen-based ions (H, H +, H 2 +, H 3 + etc.) from CxHy, with the bombardment being anisotropic in a direction parallel to flanks of the gate and so as to modify an upper portion of the thickness of the nitride-based layer at the level of the flanks of the gate only, while keeping non-modified portions (152a, 152b) of the nitride-based layer covering the flanks of the gate. ∘ plasma chemical species containing carbon from CxHy form a carbon film specifically on surfaces parallel to the direction of the bombardment; ∘ plasma creates a bombardment with ions heavier than hydrogen which prevents said carbon-containing plasma chemical species from CxHy from forming a carbon film, more particularly on the surfaces of the nitride-based layer which are perpendicular to the direction of the bombardment. - at least a step of removing the nitride-based modified layer using a selective etching of the nitride-based modified layer relative to non-modified portions (152a, 152b) of the nitride-based layer.