A semiconductor device and its manufacturing method are presented. The manufacturing method includes: providing a semiconductor structure comprising: an interlayer dielectric layer, a first metal layer surrounded by the interlayer dielectric layer, and a semiconductor layer on the interlayer dielectric layer; etching the semiconductor layer to form an opening exposing the interlayer dielectric layer, wherein the opening comprises a first opening and a second opening on the first opening; forming an insulation layer on the semiconductor structure; etching the insulation layer and the interlayer dielectric layer at the bottom of the first opening to form a groove exposing a portion of the first metal layer; forming a second metal layer on the insulation layer and on the bottom and a side surface of the groove; and patterning the second metal layer. The second metal layer in this inventive concept can be removed more completely than conventional methods.