Semiconductor device and fabrication method thereof

1. A method for fabricating a semiconductor device, comprising:

providing a semiconductor substrate, wherein the semiconductor substrate includes a dense region and a sparse region;

forming initial fins equally spaced apart from one another on the semiconductor substrate, the initial fins including a first fin group, a second fin group, and dummy fins, wherein the first fin group is formed on the sparse region of the semiconductor substrate, the second fin group is formed on the dense region of the semiconductor substrate, the first fin group and the second fin group each includes a plurality of intrinsic fins, a spatial density of the intrinsic fins on the dense region is greater than a spatial density of the intrinsic fins on the sparse region, and the dummy fins are formed on both sides of the first fin group, on both sides of the second fin group, and between adjacent intrinsic fins on the sparse region, respectively;

forming a first isolation layer on the semiconductor substrate, wherein the first isolation layer covers a portion of sidewalls of the dummy fins and a portion of sidewalls of the intrinsic fins;

forming first trenches in the first isolation layer by removing the dummy fins; and

forming a second isolation layer in the first trenches.

2. The method according to claim 1 , further including:

before forming the first isolation layer, forming additional fins on the semiconductor substrate to provide a plurality of discrete fin rings, wherein:

each fin ring includes initial fins and additional fins arranged along a rectangle shape,

the initial fins are arranged as opposite sides, and

the additional fins are arranged as opposite sides of the rectangle shape.

3. The method according to claim 2 , wherein:

after forming the first isolation layer, the first isolation layer further covers a portion of sidewalls of the additional fins; and

second trenches are formed in the first isolation layer by removing the additional fins when removing the dummy fins, wherein after forming the second isolation layer, the second isolation layer is further formed in the second trenches.

4. The method according to claim 2 , wherein forming the plurality of fin rings includes:

forming a fin material layer on both the dense region and the sparse region of the semiconductor substrate;

forming a plurality of discrete sacrificial layers on the fin material layer;

forming first sidewall spacers and second sidewall spacers arranged along a rectangle shape on sidewalls of each sacrificial layer, wherein the first sidewall spacers are arranged as opposite sides, and the second sidewall spacers are arranged as opposite sides of the rectangle shape;

after forming the first sidewall spacers and the second sidewall spacers, removing the sacrificial layers;

after removing the sacrificial layers, etching the fin material layer using the first sidewall spacers and the second sidewall spacers as a mask to form the plurality of fin rings on both the dense region and the sparse region of the semiconductor substrate; and

after etching the fin material layer using the first sidewall spacers and the second sidewall spacers as a mask, removing the first sidewall spacers and the second sidewall spacers.

5. The method according to claim 1 , wherein forming the first isolation layer includes:

forming a first isolation material layer on the semiconductor substrate, on the dummy fins, on the first fin group, and on the second fin group; and

forming the first isolation layer from the first isolation material layer by back-etching a portion of the first isolation material layer.

6. The method according to claim 1 , further including:

before removing the dummy fins, forming a mask protection layer on surfaces of the intrinsic fins and on a top surface of the first isolation layer, wherein the mask protection layer exposes surfaces of the dummy fins;

removing the dummy fins by etching using the mask protection layer as a mask to form the first trenches in the first isolation layer; and

after forming the second isolation layer, removing the mask protection layer.

7. The method according to claim 6 , wherein:

when removing the dummy fins by etching, a ratio of an etching rate on the dummy fins over an etching rate on the mask protection layer is in a range of approximately 100:1-1000:1.

8. The method according to claim 6 , wherein:

the mask protection layer is a single-layer structure; and

the mask protection layer is made of one of silicon nitride, silicon carbonitride, silicon boron nitride, titanium nitride, and tantalum nitride.

9. The method according to claim 6 , wherein:

the mask protection layer is a stacked-layer structure; and

the mask protection layer includes a first protection layer and a second protection layer on a surface of the first protection layer, wherein the first protection layer is formed on the surfaces of the intrinsic fins and on the top surface of the first isolation layer, and the first protection layer exposes the surfaces of the dummy fins.

10. The method according to claim 9 , wherein:

the first protection layer is made of silicon oxide; and

the second protection layer is made of one of silicon nitride, silicon carbonitride, silicon boron nitride, titanium nitride, and tantalum nitride.

11. The method according to claim 6 , further including:

before forming the mask protection layer, forming a mask protection material layer on the surfaces of the intrinsic fins, on the surfaces of the dummy fins, and on the top surface of the first isolation layer;

forming a planarization layer on the mask protection material layer, wherein an entire top surface of the planarization layer is above the mask protection material layer on the top surfaces of the intrinsic fins and the mask protection material layer on the top surfaces of the dummy fins;

forming a bottom anti-reflective layer on a surface of the planarization layer;

forming a patterned photoresist layer on a surface of the bottom anti-reflective layer;

forming a plurality of first openings penetrating through the bottom anti-reflective layer and the planarization layer by etching the bottom anti-reflective layer and the planarization layer using the photoresist layer as a mask, wherein a first opening exposes the mask protection material layer on a surface of a dummy fin;

removing the mask protection material layer at bottoms of the plurality of first openings to enable the first opening to expose the surface of the dummy fin and to form the mask protection layer from the mask protection material layer;

after removing the mask protection material layer at the bottoms of the plurality of first openings, removing the photoresist layer, the bottom anti-reflective layer, and the planarization layer; and

after removing the photoresist layer, the bottom anti-reflective layer, and the planarization layer, removing the dummy fins by etching using the mask protection layer as a mask.

12. The method according to claim 11 , wherein:

forming the mask protection material layer includes an atomic layer deposition process.

13. The method according to claim 6 , wherein forming the second isolation layer in the first trenches includes:

forming a second isolation material layer in the first trenches and on the mask protection layer;

planarizing the second isolation material layer until the mask protection layer on the top surfaces of the intrinsic fins are exposed to form a second isolation transition layer from the second isolation material layer; and

back-etching a portion of the second isolation transition layer using the mask protection layer as a mask to form the second isolation layer.

14. The method according to claim 13 , wherein:

planarizing the second isolation material layer includes one of a chemical mechanical polishing process and a back-etching process.

15. The method according to claim 13 , wherein:

forming the second isolation material layer includes a fluid chemical vapor deposition process.

16. The method according to claim 1 , wherein:

the first isolation layer is made of silicon oxide; and

the second isolation layer is made of silicon oxide.

17. The method according to claim 1 , further including:

forming a first gate structure on the first isolation layer and on the second isolation layer, wherein the first gate structure crosses a length portion of an intrinsic fin on the sparse region, and covers a portion of each of top and sidewall surfaces of the intrinsic fin on the sparse region; and

forming a second gate structure on the first isolation layer and on the second isolation layer, wherein the second gate structure crosses a length portion of the intrinsic fin on the dense region, and covers a portion of each of top and sidewall surfaces of the intrinsic fin on the dense region.