Semiconductor device and method for fabricating the same

A method for fabricating semiconductor device, comprising:

• providing a substrate having a logic region and high-voltage (HV) region;
• forming a first gate structure and a first gate dielectric layer on the logic region and a second gate structure and a second gate dielectric layer on the HV region, wherein a thickness of the second gate dielectric layer is greater than a thickness of the first gate dielectric layer;
• forming a contact etch stop layer (CESL) on the first gate structure and the second gate structure;
• forming an interlayer dielectric (ILD) layer around the first gate structure and the second gate structure and on the CESL;
• forming a patterned hard mask on the HV region while the CESL is on top of the first gate structure, wherein the patterned hard mask comprises a buffer layer and a cap layer;
• using the patterned hard mask to remove the CESL on the first gate structure;
• and
• transforming the first gate structure into a metal gate.