Semiconductor structure and forming method thereof

The invention discloses a semiconductor structure and a forming method thereof .The method comprises the steps: providing a substrate, and enabling the surface of the substrate to be provided with a first dielectric layer; forming a first opening in the first dielectric layer, wherein a part of the surface of the substrate is exposed from the bottom of the first opening; forming an initial first plug in the first opening; etching back the initial first plug, and forming a groove and a first plug located at the bottom of the groove in the first dielectric layer; forming a second plug in the groove, wherein the material of the first plug is different from that of the second plug; forming a second dielectric layer on the surfaces of the second plug and the first dielectric layer; etching a part of the second dielectric layer, forming a second opening in the second dielectric layer, and exposing the top surface of the second plug from the bottom of the second opening; and forming a third plug in the second openin