Semiconductor structure and fabrication method thereof

A method for forming a semiconductor structure, comprising:

• providing a substrate, wherein the substrate includes a first region and a second region adjacent to the first region;
• forming a first gate structure and first source-drain doped layers, wherein the first gate structure is formed over the first region, and the first source-drain doped layers are formed in the first region of the substrate on both sides of the first gate structure, respectively;
• forming a second gate structure and second source-drain doped layers, wherein the second gate structure is formed over the second region, and the second source-drain doped layers are formed in the second region of the substrate on both sides of the second gate structure, respectively;
• forming a first protection layer over the second gate structure;
• forming a first conductive structure over a first source-drain doped layer of the first source-drain doped layers, wherein the first conductive structure is also formed on the first gate structure, and a top surface of the first conductive structure is lower than a top surface of the first protection layer;
• forming an isolation layer over the first conductive structure;
• and
• forming a first dielectric layer over the substrate, wherein the first dielectric layer covers the first gate structure, the second gate structure, the first source-drain doped layers, the second source-drain doped layers, the first protection layer, the first conductive structure, and the isolation layer, and the first dielectric layer exposes top surfaces of the isolation layer and the first protection layer.