Non-planar FET

1. A non-planar FET, comprising:

a substrate;

a fin structure disposed on the substrate, wherein the fin structure comprises an octagonal shape from end to end in the cross section parallel to a gate and a first part adjacent to the substrate wherein the first part shrinks toward a side of the substrate;

a shallow trench isolation disposed in the substrate and surrounding the fin structure, wherein a top surface of the shallow trench isolation is leveled with a bottom surface of the fin structure and a top surface of the substrate is higher than the top surface of the shallow trench isolation;

a source/drain region disposed in the fin structure;

the gate disposed on the fin structure, wherein the gate crosses the first part; and

a gate dielectric layer disposed between the gate and the fin structure.

2. The non-planar FET according to claim 1 , wherein the first part of the fin structure comprises a bottom surface and two sidewalls encompassing the bottom surface, wherein the bottom surface directly contacts the substrate.

3. The non-planar FET according to claim 1 , wherein the first part of the fin structure has a trapezoidal shape in the cross section.

4. The non-planar FET according to claim 1 , wherein the fin structure further comprises a second part disposed on the first part.

5. The non-planar FET according to claim 4 , wherein the second part of the fin structure has a trapezoidal shape and a rectangular shape in the cross section.

6. The non-planar FET according to claim 5 , wherein the trapezoidal part of the second part shrinks toward an opposite side of the substrate.

7. The non-planar FET according to claim 5 , wherein the gate crosses the second part.