Method for manufacturing semiconductor device capable of preventing gate-to-drain capacitance and eliminating birds beak formation

A method for manufacturing a MOSFET, comprising the sequential steps of:

• providing a substrate having a gate structure thereon, wherein the gate structure has a plurality of sidewalls, and wherein the substrate and the gate structure have crystal defects;
• forming offset spacers on the sidewalls of the gate structure, wherein the offset spacers have a plurality of exterior sidewalls;
• performing an annealing operation after the offset spacers are formed, wherein the annealing operation eliminates the crystal defects;
• performing a first ion implantation using the gate structure and the offset spacers as a mask to form lightly doped drain regions in the substrate;
• forming secondary spacers on the exterior sidewalls of the offset spacers;
• and
• performing a second ion implantation using the gate structure, the offset spacers and the secondary spacers as a mask to form source/drain regions in the substrate.