Fin field-effect transistor structure and method for forming the same

1. A fin field-effect transistor (FinFET) structure, comprising:

a first fin structure protruding from a first region of a substrate;

a second fin structure protruding from a second region of the substrate;

isolation regions covering a lower portion of the first fin structure and a lower portion of the second fin structure and leaving an upper portion of the first fin structure and an upper portion of the second fin structure above the isolation regions;

a first liner layer between the lower portion of the first fin structure and the isolation regions in the first region; and

a second liner layer covering the lower portion of the second fin structure and between the second fin structure and the isolation regions in the second region,

wherein the first liner layer and the second liner layer are formed of different materials, and the first liner layer and the second liner layer are in direct physical contact with the isolation regions.

2. The FinFET structure as claimed in claim 1 , wherein the first region is a PMOS region and the second region is an NMOS region.

3. The FinFET structure as claimed in claim 2 , wherein a portion of the first fin structure is formed of silicon germanium, and the second fin structure is formed of silicon.

4. The FinFET structure as claimed in claim 3 , wherein the first liner layer is formed of a nitride-containing material, the second liner layer is formed of an oxide-containing material.

5. The FinFET structure as claimed in claim 1 , wherein the first fin structure is positioned beside the second fin structure, and the first and second fin structures are separated from each other through one of the isolation regions, which is surrounded by both the first liner layer and the second liner layer.

6. The FinFET structure as claimed in claim 1 , wherein each of the first fin structure and the second fin structure comprises source/drain regions and a channel region between the source/drain regions, the FinFET structure further comprising:

a first gate structure over the channel region of the first fin structure in the first region;

first gate spacers on opposite sidewalls of the first gate structure;

first source/drain features in the source/drain regions of the first fin structure and adjacent to outer sidewalls of the first gate spacers;

a second gate structure over the channel region of the second fin structure in the second region;

second gate spacers on opposite sidewalls of the second gate structure; and

second source/drain features in the source/drain regions of the second fin structure and adjacent to outer sidewalls of the second gate spacers.

7. A Fin Field-Effect Transistor (FinFET) structure, comprising:

a first fin structure comprising silicon germanium in a first region of a substrate;

a second fin structure formed of silicon in a second region of the substrate;

an isolation region covering a lower portion of the first fin structure and a lower portion of the second fin structure and leaving an upper portion of the first fin structure and an upper portion of the second fin structure above the isolation regions;

a first liner layer formed of a nitride-containing material covering the lower portion of the first fin structure, so that the first fin structure is separated from the isolation region through the first liner layer; and

a second liner layer formed of an oxide-containing material covering the lower portion of the second fin structure so that the second fin structure is separated from the isolation region through the second liner layer, wherein the first liner layer is formed without overlapping the second liner layer in the second region.

8. The FinFET structure as claimed in claim 7 , wherein the first fin structure is separated from the first liner layer through a semiconductor capping layer covering the lower portion of the first fin structure.

9. The FinFET structure as claimed in claim 7 , wherein the first region is a PMOS region and the second region is an NMOS region.

10. The FinFET structure as claimed in claim 7 , wherein the isolation region is surrounded by both the first liner layer and the second liner layer.

11. The FinFET structure as claimed in claim 7 , wherein each of the first fin structure and the second fin structure comprises source/drain regions and a channel region between the source/drain regions, the FinFET structure further comprising:

a first gate structure over the channel region of the first fin structure in the first region;

first gate spacers on opposite sidewalls of the first gate structure;

first source/drain features in the source/drain regions of the first fin structure and adjacent to outer sidewalls of the first gate spacers;

a second gate structure over the channel region of the second fin structure in the second region;

second gate spacers on opposite sidewalls of the second gate structure; and

second source/drain features in the source/drain regions of the second fin structure and adjacent to outer sidewalls of the second gate spacers.

12. A method for forming a fin field-effect transistor (FinFET) structure, comprising:

forming a first fin structure in a first region of a substrate and a second fin structure in a second region of the substrate;

forming a semiconductor capping layer over the first fin structure and the second fin structure;

forming a first liner layer over the semiconductor capping layer in the first region and the second region;

forming a mask layer to cover the first liner layer in the first region;

removing the first liner layer in the second region;

forming a second liner layer over the second fin structure;

removing the mask layer after the second liner layer is formed;

forming isolation regions covering a lower portion of the first fin structure and a lower portion of the second fin structure and leaving an upper portion of the first fin structure and an upper portion of the second fin structure above the isolation regions;

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

forming a second gate structure over the second fin structure.

13. The method for forming a FinFET structure as claimed in claim 12 , wherein forming the first fin structure and forming the second fin structure comprises:

removing a portion of the substrate comprising silicon in the first region;

epitaxially growing a semiconductor material comprising silicon germanium in the first region; and

forming trenches in the semiconductor material in the first region and in the substrate in the second region, wherein the first fin structure and the second fin structure are formed between the trenches.

14. The method for forming a FinFET structure as claimed in claim 12 , wherein forming the isolation regions comprises:

forming an insulation material over the first fin structure and the second fin structure;

removing the insulation material, the first liner layer, the second liner layer and the semiconductor capping layer over a top surface of the first fin structure and a top surface of the second fin structure;

removing the insulation material, the first liner layer, the second liner layer and the semiconductor capping layer covering the upper portion of the first fin structure and the upper portion of the second fin structure.

15. The method for forming a FinFET structure as claimed in claim 14 , further comprising:

performing a first anneal process after forming the insulation material over the first fin structure and the second fin structure; and

performing a second anneal process after removing the insulation material, the second liner layer over the top surface of the first fin structure and a top surface of the second fin structure.

16. The method for forming a FinFET structure as claimed in claim 15 , wherein performing each of the first anneal process and the second anneal process comprises:

performing a wet steam anneal process; and

performing a dry anneal process after the wet steam anneal process.

17. The method for forming a FinFET structure as claimed in claim 16 , wherein the dry anneal process is performed in an ambient atmosphere comprising nitrogen.

18. The method for forming a FinFET structure as claimed in claim 12 , wherein each of the first fin structure and the second fin structure comprises source/drain regions and a channel region between the source/drain regions, the method further comprising:

forming a first gate structure over the channel region of the first fin structure in the first region;

forming first gate spacers on opposite sidewalls of the first gate structure;

forming first source/drain features in the source/drain regions and adjacent to outer sidewalls of the first gate spacers;

forming a second gate structure over the channel region of the second fin structure in the second region;

forming second gate spacers on opposite sidewalls of the second gate structure; and

forming second source/drain features in the second source/drain regions of the second fin structure and adjacent to outer sidewalls of the second gate spacers.

19. The FinFET structure as claimed in claim 1 , wherein the first liner layer is formed without overlapping the second liner layer in the second region.

20. The FinFET structure as claimed in claim 1 , wherein a semiconductor capping layer between the lower portion of the first fin structure and the first liner layer in the first region, wherein a bottommost surface of the semiconductor capping layer is level with a bottommost surface of the second liner layer.