Method to form convex structure on surface of semiconductor material

1. A method to form a lens on a semiconductor material monolithically, comprising steps of:

forming an intermediate layer on a surface of the semiconductor material made of InP, the intermediate layer being made of silicon oxide, silicon nitride or silicon oxy-nitride;

forming a mask layer on the intermediate layer, the mask layer having a first photoresist having a circular shape and a second photoresist that is spaced from the first photoresist and surrounds the first photoresist;

deforming the first photoresist to have a hemispherical or convex shape by thermal treatment;

transcribing the shape of the mask layer on the intermediate layer to form a processed intermediate layer by etching the mask layer and the intermediate layer to expose the surface of the semiconductor material, the processed intermediate layer having a first processed intermediate layer having a circular shape and a second processed intermediate layer that is spaced from the first processed intermediate layer and surrounds the first processed intermediate layer;

forming a third photoresist so as to cover the first processed intermediate layer and the second processed intermediate layer;

removing a region of the third photoresist on the first processed intermediate layer and leaving another region of the third photoresist on the second processed intermediate layer; and

transcribing the shape of the first processed intermediate layer on the surface of the semiconductor material to form the lens in the semiconductor material.

2. The method of claim 1 ,

wherein the shape of the first processed intermediate layer has a curvature greater than a curvature of the shape of the first photoresist.

3. The method of claim 2 ,

wherein the lens has a curvature less than the curvature of the first processed intermediate layer.

4. The method of claim 1 ,

wherein the step of transcribing the mask layer on the intermediate layer is carried out by first dry-etching using a gas containing fluorine and oxygen, and

wherein the step of transcribing the processed intermediate layer on the semiconductor material is carried out by second dry-etching using another gas containing fluorine and halogen.

5. The method of claim 4 ,

wherein the intermediate layer has an etching rate less than an etching rate of the mask layer in the first dry-etching, and

wherein the intermediate layer has an etching rate less than an etching rate of the semiconductor material in the second dry-etching.

6. The method of claim 1 ,

further including a step, before the formation of the intermediate layer, fixing the semiconductor material on a support made of silica glass.