Structure and formation method of semiconductor device with fin structures

1. A method for forming a semiconductor device structure, comprising:

forming a fin structure over a semiconductor substrate;

forming an isolation layer over the fin structure and the semiconductor substrate;

forming a protective layer over the isolation layer;

forming a dielectric layer over the protective layer; and

partially removing the isolation layer, the protective layer, and the dielectric layer, wherein a remaining portion of the isolation layer forms an isolation structure, remaining portions of the protective layer and the dielectric layer form a dielectric fin, the remaining portion of the protective layer forms a protective shell of the dielectric fin, the remaining portion of the dielectric layer forms a dielectric structure of the dielectric fin, the isolation structure laterally surrounds a lower portion of the fin structure and a lower portion of the dielectric fin, the protective shell has a first dielectric constant, the dielectric structure has a second dielectric constant, the first dielectric constant is higher than the second dielectric constant, the protective shell has a first average grain size, the dielectric structure has a second average grain size, and the first average grain size is larger than the second average grain size.

2. The method for forming a semiconductor device structure as claimed in claim 1 , further comprising heating the protective layer to at least partially crystallize the protective layer.

3. The method for forming a semiconductor device structure as claimed in claim 2 , wherein the crystallization of the protective layer is performed during the formation of the dielectric layer.

4. The method for forming a semiconductor device structure as claimed in claim 2 , wherein the crystallization of the protective layer is performed before the formation of the dielectric layer.

5. The method for forming a semiconductor device structure as claimed in claim 1 , further comprising:

forming a dummy gate stack covering a portion of the dielectric fin and a portion of the fin structure;

forming a first epitaxial structure over the fin structure; and

forming a second epitaxial structure over the semiconductor substrate, wherein the dielectric fin is between the first epitaxial structure and the second epitaxial structure.

6. The method for forming a semiconductor device structure as claimed in claim 5 , wherein the first epitaxial structure is in direct contact with the dielectric fin.

7. The method for forming a semiconductor device structure as claimed in claim 6 , wherein the second epitaxial structure is in direct contact with the dielectric fin.

8. The method for forming a semiconductor device structure as claimed in claim 5 , further comprising:

partially removing the fin structure before the formation of the first epitaxial structure and the second epitaxial structure, wherein the dielectric structure is also partially removed during the partial removal of the fin structure such that a topmost surface of the dielectric structure is closer to the semiconductor substrate than a topmost surface of the protective shell.

9. The method for forming a semiconductor device structure as claimed in claim 8 , further comprising:

forming a protective cap over the dielectric structure, wherein a topmost surface of the protective cap is substantially level with the topmost surface of the protective shell.

10. A method for forming a semiconductor device structure, comprising:

forming a first fin structure and a second fin structure over a substrate;

forming a dielectric fin over the substrate, wherein the dielectric fin is between the first fin structure and the second fin structure, the dielectric fin has a dielectric structure and a protective shell, the protective shell extends along sidewalls and a bottom of the dielectric structure, the protective shell has a first dielectric constant, the dielectric structure has a second dielectric constant, and the first dielectric constant is higher than the second dielectric constant;

removing an upper portion of the dielectric structure; and

forming a protective cap over a remaining portion of the dielectric structure.

11. The method for forming a semiconductor device structure as claimed in claim 10 , further comprising:

forming a first epitaxial structure over the first fin structure; and

forming a second epitaxial structure over the second fin structure.

12. The method for forming a semiconductor device structure as claimed in claim 11 , further comprising:

forming a dummy gate stack partially covering the first fin structure, the second fin structure, and the dielectric fin before the formation of the first epitaxial structure and the second epitaxial structure;

removing the dummy gate stack after the formation of the first epitaxial structure and the second epitaxial structure; and

forming a metal gate stack partially covering the first fin structure, the second fin structure, and the dielectric fin.

13. The method for forming a semiconductor device structure as claimed in claim 12 , further comprising:

forming an insulating structure in the metal gate stack extending from an upper surface of the metal gate stack towards the dielectric fin, wherein the metal gate stack has a first portion and a second portion, the insulating structure is between the first portion and the second portion, and the first portion is electrically isolated from the second portion.

14. A method for forming a semiconductor device structure, comprising:

forming a first fin structure and a second fin structure over a substrate;

forming a dielectric fin over the substrate, wherein the dielectric fin is between the first fin structure and the second fin structure, the dielectric fin has a dielectric structure and a protective shell, the protective shell extends along sidewalls and a bottom of the dielectric structure; and

at least partially crystallizing the protective shell to form a crystallized protective shell, wherein the crystallization of the protective layer is performed during the formation of the dielectric layer or the crystallization of the protective layer is performed before the formation of the dielectric layer.

15. The method for forming a semiconductor device structure as claimed in claim 14 , wherein the crystallized protective shell has a first average grain size, the dielectric structure has a second average grain size, and the first average grain size is larger than the second average grain size.

16. The method for forming a semiconductor device structure as claimed in claim 14 , wherein the crystallized protective shell has a first dielectric constant, the dielectric structure has a second dielectric constant, and the first dielectric constant is higher than the second dielectric constant.

17. The method for forming a semiconductor device structure as claimed in claim 16 , further comprising:

forming a protective cap over the dielectric fin, wherein the protective cap has a third dielectric constant, and the third dielectric constant is higher than the second dielectric constant.

18. The method for forming a semiconductor device structure as claimed in claim 14 , further comprising:

forming a first epitaxial structure over the first fin structure; and

forming a second epitaxial structure over the second fin structure, wherein at least one of the first epitaxial structure and the second epitaxial structure is in direct contact with the crystallized protective shell of the dielectric fin.

19. The method for forming a semiconductor device structure as claimed in claim 14 , further comprising:

partially removing the dielectric structure such that a topmost surface of the dielectric structure is closer to the semiconductor substrate than a topmost surface of the protective shell.

20. The method for forming a semiconductor device structure as claimed in claim 14 , wherein a bottommost surface of the protective shell is closer to the semiconductor substrate than a bottommost surface of the dielectric structure.