Semiconductor device and method for fabricating the same

1. A semiconductor device, comprising:

a substrate having a first region and a second region;

a first fin-shaped structure on the first region and a second fin-shaped structure on the second region;

a shallow trench isolation (STI) around the first fin-shaped structure and the second fin-shaped structure;

a first oxide layer on the first fin-shaped structure;

a second oxide layer on and directly contacting the first oxide layer and the STI; and

a third oxide layer on the second fin-shaped structure having a width less than a width of the first fin-shaped structure, wherein a thickness of the third oxide layer is less than a thickness of the first oxide layer and different from a thickness of the second oxide layer and the thickness of the first oxide layer on the first region is less than the thickness of the second oxide layer on the first region.

2. The semiconductor device of claim 1 , wherein a thickness of the first oxide layer is less than a thickness of the second oxide layer.

3. The semiconductor device of claim 1 , further comprising:

a first liner on the first fin-shaped structure;

a second liner on the first liner; and

a dielectric layer on the second liner and around the first fin-shaped structure.

4. The semiconductor device of claim 3 , wherein the first liner and the second liner comprise silicon oxide.

5. The semiconductor device of claim 3 , wherein a thickness of the first liner is greater than a thickness of the first oxide layer.