Semiconductor structure and forming method thereof

The invention discloses a semiconductor structure and a forming method thereof, and the semiconductor structure comprises a substrate which is provided with an interlayer dielectric layer; a gate structure on the substrate; the source-drain doping layer is positioned in the substrate on two sides of the gate structure; the first opening is located in the interlayer dielectric layer, and the first opening exposes the top of the gate structure; the first inner side walls are located on the side wall of the first opening, and a first gap is formed between the first inner side walls; the second opening is located in the interlayer dielectric layer, and the second opening exposes the top of the source-drain doping layer; the conductive layer is located in the second opening, and the top surface of the conductive layer is lower than the top surface of the interlayer dielectric layer; the second inner side walls are located on the side walls of the second openings exposed out of the conductive layer, and a second ga