Method for manufacturing a metal gate

1. A method for manufacturing a semiconductor structure, the method comprising:

providing a semiconductor substrate;

uniformly depositing a first hard mask layer on the semiconductor substrate;

corresponding to a region where a first metal gate is located, patterning and etching the first hard mask layer to form a recess;

forming a sloping sidewall on a sidewall of the recess, the sloping sidewall and an upper surface of the substrate forming a groove structure, wherein a size of an upper part of the groove structure being larger than a lower part;

forming a second metal gate in the groove structure, wherein the forming of the second metal gate further comprises:

depositing a polysilicon layer on the upper surface of the first hard mask layer and in the groove structure;

planarizing the polysilicon layer to remove polysilicon from the upper surface of the first hard mask layer to form a dummy gate in the groove structure;

depositing a second hard mask layer on the upper surfaces of the first hard mask layer and the dummy gate;

corresponding to a region other than the side wall and the dummy gate, patterning and etching the second hard mask layer and the first hard mask layer, and reserving the sidewall, the dummy gate and the second hard mask layer covering the upper surface of the dummy gate;

depositing a dielectric layer on the semiconductor substrate to cover the semiconductor substrate and the upper surface of the second hard mask layer;

planarizing the dielectric layer, and removing the second hard mask layer covering the upper surface of the dummy gate, such that an upper surface of the dielectric layer is flush with the upper surface of the dummy gate; and

removing the dummy gate and depositing a third metal gate in the groove structure; and

removing the first hard mask layer.

2. The method of claim 1 , wherein the forming of the sloping sidewall on the sidewall of the recess comprises:

uniformly depositing a dielectric medium on an upper surface of the first hard mask layer and the sidewall and the bottom of the recess;

etching the dielectric medium covering the upper surface of the first hard mask layer and the bottom of the recess; and

reserving the dielectric medium covering the sidewall of the recess to form the sloping sidewall.

3. The method of claim 1 , further comprising:

before depositing the dielectric layer, performing ion implantation in a source region and a drain region on two sides of the dummy gate to form lightly doped drain structures.

4. The method of claim 1 , wherein material of the sidewall is the same material as the dielectric layer.