Method for producing metal plug

The invention relates to a method for producing a metal plug, comprising the following steps of: firstly, providing a semiconductor wafer having an interconnection layer, and forming a dielectric layer, an insulation layer and a protective layer on the wafer in sequence, wherein the protective layer is made of silicon nitride; etching the protective layer, the insulation layer and the dielectric layer to form an opening for exposing the interconnection layer, and depositing a metal layer in the opening and on the protective layer; and flattening the metal layer and removing the protective layer and the insulation layer to form the metal plug. Due to the adoption of the production method, the deformation of a copper circuit can be prevented when the metal layer is flattened ands the quality of the wafer and the reliability of the subsequence process can be ensured.