Manufacturing method of semiconductor device

The invention provides a manufacturing method of a semiconductor device. The method comprises the steps of providing a semiconductor substrate, wherein a dielectric layer and a groove arranged in thedielectric layer are formed on the semiconductor substrate; forming a work function layer in the dielectric layer and the channel; modifying the work function layer; and filling the groove with metal,and performing chemical and mechanical grinding to expose the dielectric layer. According to the manufacturing method of the semiconductor device, oxygen processing is performed on the semiconductorsubstrate formed with the work function layer, so that oxygen is introduced to the work function layer, the work function layer is modified, the crystal grain size of a metal material layer sequentially grown and formed on the work function layer is smaller than the crystal grain size of the metal material layer which is grown and formed without oxygen processing, and the grinding uniformity during the chemical and mechanic