Method for forming under a thin layer of a first material portions of another material and/or empty areas
A method for forming an empty area under a layer of a given material, including forming on a substrate a stacking of a photosensitive layer and of a layer of the given material; insolating a portion of the photosensitive layer or its complement according to whether the photosensitive layer is positive or negative with an electron beam crossing the layer of the given material; and removing the portion of the photosensitive layer.
1. A method for forming a gate-all-around transistor, the method comprising:
forming a single-crystal silicon bridge running above an active area of a semiconductor substrate, the bridge being laid on an insulation area surrounding the active area;
forming a thin silicon oxide layer around the bridge and on the active area;
depositing a photosensitive layer to cover the bridge and the insulation area surrounding the active area, and into an empty space located between the active area and the bridge;
simultaneously insolating, through the silicon bridge and the thin silicon oxide layer, first and second portions of the photosensitive layer, the first portion positioned above a central portion of the bridge and the second portion positioned below the central portion of the bridge;
removing the first and second portions of the photosensitive layer;
filling spaces previously occupied by the said first and second portions of the photosensitive layer with a conductive material to form a gate; and
removing the remaining portions of the photosensitive layer.
2. The method of claim 1 , further comprising:
covering the gate, bridge, and empty spaces located under the bridge on both sides of the gate with a silicon nitride; and
performing an anisotropic etch of the nitride to form spacers on the sides of the gate portion located above the bridge.
3. The method of claim 1 , wherein the first and second portions are superposed.
4. The method of claim 1 , wherein simultaneously insolating first and second portions of the photosensitive layer comprises insolating with an electron beam crossing the silicon bridge and the thin silicon oxide layer.
5. The method of claim 1 , wherein forming the single-crystal silicon bridge comprises forming a first portion of the bridge that is disposed directly above the active area of the semiconductor substrate and a second portion of the bridge that bears against the insulation area surrounding the active area, wherein the first portion of the bridge is elevated with respect to the second portion of the bridge.
6. The method of claim 1 , wherein the first and second portions of the photosensitive layer are aligned.