Manufacturing method of semiconductor structure

A manufacturing method of a semiconductor structure, comprising:

• forming gate structures on a substrate, wherein each of the gate structures comprises:
• a gate, disposed on the substrate;
• a first spacer, disposed on a sidewall of the gate;
• and
• a second spacer, disposed on the first spacer,
• wherein in a region between two adjacent gate structures, the first spacers are separated from each other, and the second spacers are separated from each other;
• forming a protective layer in the region between the two adjacent gate structures, wherein the protective layer covers lower portions of the second spacers and exposes upper portions of the second spacers, and a top surface of the protective layer is lower than top surfaces of the second spacers;
• removing a part of the upper portions of the second spacers using the protective layer as a mask to enlarge a distance between the upper portions of the second spacers, wherein each of the second spacers has a recess, and an entire surface of the recess is a concave curved surface;
• and
• removing the protective layer.