Semiconductor device and method

1. A method comprising:

forming a channel structure over a substrate;

forming a first isolation structure extending in a direction parallel to the channel structure;

forming a dummy gate structure over the channel structure and the first isolation structure;

depositing a hard mask layer over the dummy gate structure;

etching the hard mask layer to form a first opening through the hard mask layer over the first isolation structure;

conformally depositing a first dielectric layer over the hard mask layer, in the first opening, and over the dummy gate structure;

etching the first dielectric layer to extend the first opening and expose the dummy gate structure; and

etching the dummy gate structure to extend the first opening and expose the first isolation structure.

2. The method of claim 1 , wherein forming the first isolation structure comprises:

forming a first dummy structure over the substrate;

forming an isolation region adjacent the channel structure and the first dummy structure;

etching the first dummy structure to form a second opening in the isolation region; and

forming the first isolation structure in the second opening.

3. The method of claim 1 , wherein the dummy gate structure comprises polycrystalline silicon, and wherein the first dielectric layer comprises silicon nitride.

4. The method of claim 1 , further comprising depositing a gate isolation structure in the first opening after etching the dummy gate structure.

5. The method of claim 4 , further comprising removing the hard mask layer and the first dielectric layer using a planarization process.

6. The method of claim 5 , further comprising:

removing the dummy gate structure to form a second opening; and

forming a replacement gate structure in the second opening, the replacement gate structure contacting the first isolation structure and the gate isolation structure.

7. A method comprising:

forming a gate structure over a semiconductor substrate;

depositing a hard mask over the gate structure;

etching the hard mask to form a first opening exposing the gate structure;

depositing a first dielectric layer in the first opening;

etching the first dielectric layer to form a first spacer and expose the gate structure; and

etching the gate structure to expose a dielectric fin disposed between the gate structure and the semiconductor substrate.

8. The method of claim 7 , wherein the gate structure comprises polycrystalline silicon, and wherein the first dielectric layer comprises silicon nitride.

9. The method of claim 7 , wherein the gate structure comprises polycrystalline silicon, wherein the first dielectric layer comprises silicon, and wherein etchants for etching the first dielectric layer are the same as etchants for etching the gate structure.

10. The method of claim 7 , wherein the gate structure comprises polycrystalline silicon, and wherein the first dielectric layer comprises silicon oxide.

11. The method of claim 7 , further comprising depositing a second dielectric layer in the first opening over the first dielectric layer, wherein etching the first dielectric layer further comprises etching the second dielectric layer to expose the gate structure.

12. The method of claim 7 , further comprising:

forming a first fin structure, a second fin structure, and a third fin structure extending from the semiconductor substrate, wherein the second fin structure is between the first fin structure and the third fin structure; and

replacing the second fin structure with the dielectric fin.

13. The method of claim 12 , wherein the dielectric fin comprises silicon nitride.

14. A method comprising:

forming a hard mask over a dummy gate structure;

etching a first opening extending through the hard mask and partially through the dummy gate structure;

conformally depositing a first dielectric layer over the hard mask and the dummy gate structure and in the first opening;

simultaneously etching through the first dielectric layer and the dummy gate structure to extend the first opening; and

forming a gate isolation structure in the first opening.

15. The method of claim 14 , further comprising:

forming a first fin and a second fin extending from a semiconductor substrate, the first fin and the second fin comprising a semiconductor material;

replacing the second fin with a dielectric fin; and

forming the dummy gate structure over the first fin and the dielectric fin.

16. The method of claim 15 , wherein the dielectric fin and the gate isolation structure are formed of materials comprising silicon nitride.

17. The method of claim 16 , wherein the dummy gate structure and the first dielectric layer are formed of materials comprising polycrystalline silicon.

18. The method of claim 14 , wherein simultaneously etching through the first dielectric layer and the dummy gate structure comprises dry etching using an etchant comprising fluorine.

19. The method of claim 14 , further comprising performing a planarization process on the hard mask and the first dielectric layer to remove the hard mask, wherein at least a portion of the first dielectric layer remains after performing the planarization process.

20. The method of claim 14 , further comprising:

simultaneously removing the dummy gate structure and the first dielectric layer to form a second opening; and

forming a replacement gate structure in the second opening.