Semiconductor device and method for fabricating the same

1. A method for fabricating semiconductor device, comprising:

forming a fin-shaped structure on a substrate;

forming a gate dielectric layer on the fin-shaped structure, wherein the fin-shaped structure and the gate dielectric layer extend along a same direction in a top view;

forming a gate electrode on the fin-shaped structure;

performing a nitridation process to implant nitrogen ions into the gate dielectric layer adjacent to two sides of the gate electrode for dividing the gate dielectric layer into a first portion directly under the gate electrode and a second portion at two sides of the gate electrode;

forming a spacer on sidewalls of the gate electrode after performing the nitridation process;

forming lightly doped drain regions at the two sides of the gate electrode after performing the nitridation process;

removing a part of the second portion and a part of the fin-shaped structure to form recesses at the two sides of the gate electrode; and

forming an epitaxial layer in the recesses at the two sides of the gate electrode.

2. The method of claim 1 , wherein the first portion and the second portion comprise different materials.

3. The method of claim 2 , wherein the first portion comprises silicon oxide and the second portion comprises silicon oxynitride (SiON).

4. The method of claim 1 , wherein the fin-shaped structure and the gate dielectric layer are extended along a first direction on the substrate and the gate electrode is extended along a second direction.

5. The method of claim 4 , wherein the first direction is orthogonal to the second direction.

6. The method of claim 1 , wherein the nitridation process comprises a remote thermal nitridation process (RTN) or a decoupled plasma nitridation (DPN) process.