Process for locally dissolving the oxide layer in a semiconductor-on-insulator type structure

1. A process for treating a semiconductor-on-insulator structure that includes, successively, a support substrate, an oxide layer and a thin semiconductor layer, which comprises:

forming a nitride mask on the thin semiconductor layer to define exposed areas at the surface which are not covered by the mask and which are arranged in a desired pattern, with the mask formed to be at least partially buried in the thickness of the thin semiconductor layer; and

applying a heat treatment in a neutral or controlled reducing atmosphere and under controlled conditions of temperature and time to induce at least a portion of the oxygen of the oxide layer to diffuse through the thin semiconductor layer, thereby resulting in a controlled reduction of oxide thickness in the areas of the oxide layer corresponding to the desired pattern of the exposed areas.

2. The process of claim 1 , wherein the mask involves consumption of at least a portion of the thickness of the semiconductor layer.

3. The process of claim 1 , wherein the mask is formed of a silicon nitride or silicon oxynitride material by applying a nitrogen plasma treatment to the semiconductor layer.

4. The process of claim 1 , wherein the mask is formed by implanting nitrogen at the surface of the semiconductor layer.

5. The process of claim 1 , wherein the mask is formed by:

etching the thin semiconductor layer to form trenches at locations anticipated for the mask; and

forming the mask in the trenches.

6. The process of claim 1 , wherein the semiconductor layer is made of silicon and has a thickness smaller than 5,000 Å.

7. The process of claim 1 , wherein the semiconductor layer is made of silicon and has a thickness smaller than 2,500 Å.

8. The process of claim 3 , wherein the mask is formed by nitriding the material of the semiconductor layer, thereby resulting in consumption of a portion of the thickness of the semiconductor layer.

9. The process of claim 8 , wherein the thickness of the portion of the mask contained between the base of the mask and the free surface of the exposed areas is chosen to be substantially equal to 1.5 times the thickness of the oxide layer of the structure.

10. The process of claim 8 , wherein the thickness of the mask is between 1 and 50 nm and the nitriding step is carried out by annealing the structure in a nitrogen atmosphere at a temperature of between 700 and 1,000° C.

11. The process of claim 5 , wherein the trenches have a depth substantially equal to 1.5 times the thickness of the oxide layer of the structure.

12. The process of claim 5 , wherein the mask is formed such that the surface thereof is flush with the surface of the exposed areas of the semiconductor layer.

13. The process of claim 5 , wherein the thickness of the mask is between 1 and 50 nm and the forming of the mask includes nitrogen plasma treatment or nitriding of the trenches or nitrogen implantation at the surface of the semiconductor material of the trenches.

14. The process of claim 5 , wherein the mask is formed by:

depositing silicon nitride on the etched structure and at a thickness that is greater than the depth of the trenches; and

planarizing the deposited silicon nitride until reaching the exposed areas of the semiconductor layer.