Semiconductor structure and manufacturing method of the same

1. A semiconductor structure, comprising:

a gate element, the gate element including:

a gate dielectric layer;

a gate electrode over the gate dielectric layer;

a pair of spacers formed along sidewalls of the gate dielectric layer and the gate electrode; and

a waveguide passing through the gate electrode from a top surface of the gate electrode to a bottom surface of the gate electrode, the waveguide being directly adjacent to the gate electrode; and

a grating coupler structure beneath the waveguide.

2. The semiconductor structure of claim 1 , wherein the waveguide is filled with air.

3. The semiconductor structure of claim 1 , wherein the waveguide fully overlaps the grating coupler structure from a top view.

4. The semiconductor structure of claim 1 , wherein a bottom surface of the waveguide is isolated from the grating coupler by the gate dielectric layer.

5. The semiconductor structure of claim 1 , further comprising a contact etch stop layer covering a top surface of the gate electrode.

6. The semiconductor structure of claim 1 , wherein the gate electrode includes polysilicon.

7. The semiconductor structure of claim 1 , wherein the waveguide has a tapered structure.

8. The semiconductor structure of claim 1 , wherein the waveguide has a round bottom.

9. A semiconductor structure, comprising:

a substrate;

a grating coupler structure at least partially embedded in the substrate; and

a waveguide over the grating coupler; and

wherein a sidewall of the waveguide is encompassed by a gate element, and the gate element includes a gate dielectric layer, a gate electrode and a pair of spacers along sidewalls of the gate dielectric layer and the gate electrode.

10. The semiconductor structure of claim 9 , wherein the waveguide is filled with air.

11. The semiconductor structure of claim 9 , wherein the gate element includes:

a gate dielectric layer over the substrate;

a gate electrode over the gate dielectric layer; and

a silicon nitride layer over the gate electrode.

12. The semiconductor structure of claim 11 , wherein the sidewall of the waveguide is encompassed by the gate electrode of the gate element.

13. The semiconductor structure of claim 12 , wherein the sidewall of the waveguide is further encompassed by the silicon nitride layer of the gate element.

14. The semiconductor structure of claim 11 , wherein the waveguide is laminated on the gate dielectric layer.

15. The semiconductor structure of claim 14 , wherein a width of a bottom surface of the waveguide is narrower than a width of the gate dielectric layer.

16. The semiconductor structure of claim 11 , wherein the gate electrode includes polysilicon.

17. The semiconductor structure of claim 9 , further comprising an inter level dielectric (ILD) material including a metallization layer over the substrate.

18. The semiconductor structure of claim 17 , wherein the waveguide is further encompassed by the ILD material.

19. A method for manufacturing a semiconductor structure, comprising:

providing a semiconductor substrate;

forming a gate element over the semiconductor substrate, the gate element including a gate dielectric layer, a gate electrode over the gate dielectric layer and a pair of spacers along sidewalls of the gate dielectric layer and the gate electrode;

forming an inter level dielectric (ILD) material over the gate element;

performing a first etch to form an opening penetrating through the ILD material and stopping at the gate electrode; and

performing a second etch to expand the opening to penetrate through the gate electrode and stop at the gate dielectric layer.

20. The semiconductor structure of claim 19 , wherein the

providing the semiconductor substrate comprises:

providing the semiconductor substrate having a grating coupler structure therein.