Semiconductor device and fabrication method thereof

1. A fabrication method of a semiconductor device, comprising:

providing a base substrate;

forming an isolation structure film on the base substrate, a top portion of the isolation structure film containing a plurality of first openings therethrough;

forming a second opening at a bottom of each first opening by removing a portion of the isolation structure film to expose a surface of the base substrate, wherein, along a direction in parallel with the surface of the base substrate, the second opening has a size larger than a corresponding first opening;

forming fins in the first and second openings; and

forming an isolation structure by removing a portion of an isolation material film, wherein a top surface of the isolation structure is lower than a top surface of the fins and the isolation structure covers a portion of the sidewalls of the fins.

2. The fabrication method according to claim 1 , wherein:

a size of the first opening along a width direction of the fins is about 6 nm to about 20 nm.

3. The fabrication method according to claim 1 , wherein:

a size of the second opening along a width direction of the fins is about 10 nm to about 30 nm.

4. The fabrication method according to claim 1 , wherein:

the isolation structure film includes a first isolation material film containing the plurality of first openings therethrough, and a second isolation material film under the first isolation material film and on the base substrate, and

wherein forming the isolation structure film includes:

forming an initial isolation structure film on the base substrate, wherein the initial isolation structure film includes the second isolation material film on the base substrate and a first initial isolation material film on the second isolation material film; and

removing a portion of the first initial isolation material film to expose the second isolation material film to form the plurality of first openings passing through the first isolation material film.

5. The fabrication method according to claim 4 , wherein forming the second openings includes:

removing the second isolation material film at the bottom of each first opening to expose the surface of the base substrate to form a second initial opening, which passes through the second isolation material film; and

further removing a portion of the second isolation material film on the sidewalls of the second initial opening to form the second opening.

6. The fabrication method according to claim 5 , further including:

forming a stop layer between the first initial isolation material film and the second isolation material film, wherein the bottoms of the plurality of first openings expose the stop layer; and

before forming the second initial openings, removing a portion of the stop layer at the bottom of the each first opening.

7. The fabrication method according to claim 4 , wherein:

a thickness of the first initial isolation material film is about 800 Angstroms to about 2000 Angstroms.

8. The fabrication method according to claim 5 , wherein forming the second initial openings includes a dry etching process, including:

a gas including CH 4 , CHF 3 or a combination thereof;

a flow rate of CH 4 of about 8 sccm to about 500 sccm;

a flow rate of CHF 3 of about 30 sccm to about 200 sccm;

a power of radio frequency of about 100 W to about 1300 W;

a direct current voltage of about 80 V to about 500 V;

a time duration of about 4 s to about 500 s; and

a pressure of about 10 mtorr to about 2000 mtorr.

9. The fabrication method according to claim 1 , after forming the first openings and before forming the second openings, further including:

forming a protection layer on sidewalls of the plurality of the first openings by:

forming a protection film on the isolation structure film and on the sidewalls and bottoms of the plurality of first openings, and

removing the protection film from the isolation structure film and the bottoms of the plurality of first openings.

10. The fabrication method according to claim 9 , wherein:

the protection layer is made of a material including silicon nitride; and the isolation structure film is made of a material including silicon dioxide.

11. The fabrication method according to claim 1 , wherein forming the fins includes:

forming a fin material layer on the top of the isolation structure film, and in the first and second openings; and

planarizing the fin material layer until the isolation structure film is exposed, wherein each fin is formed in the each first and a corresponding second opening.

12. The fabrication method according to claim 1 , after forming the isolation structure, further including:

forming gate structures across fins; and

forming source/drain doped regions in the fins on sides of each gate structure.