The application provides a
semiconductor device and a preparation method thereof. In the preparation method, a
height difference exists between a top surface of a first
hard mask layer and a top surface of a second
hard mask layer; a first interlayer
dielectric layer is formed, covering the
semiconductor substrate, the first
hard mask layer and the second hard
mask layer; a first chemical mechanical
polishing process is performed, and the
polishing stops at the surfaces of the first
etching stop layer and the second
etching stop layer; the remaining first interlayer
dielectric layer is removed; the first outer sidewall, the second outer sidewall, the first
etching stop layer and the second etching stop layer are removed, and the top surfaces of the first dummy gate layer and the second dummy gate layer are of the same height; a stress layer and a second interlayer
dielectric layer are sequentially formed; and a second chemical mechanical
polishing process is performed, and the polishing stops at the surfaces of the first dummy gate layer and the second dummy gate layer. In this way, the
height difference is avoided to be continued to the underlying film layer, the NP loading effect and the disc-shaped defect caused by the
height difference are eliminated, and the device performance is improved.