A film thickness distribution exists in a substrate plane after CMP step. This film thickness distribution results in, for example, variation in gate threshold value voltages of metal gates, and causes variation in element characteristics. It is an object of the present invention to easily improve the film thickness distribution processed by this CMP step.By using the ion beam etching method after the CMP step, the film thickness distribution in the plane of the substrate 111 is corrected. More specifically, when the ion beam etching is performed, the plasma density in the plasma generation chamber 102 is caused to be different between a position facing a central portion in the plane of the substrate 111 and a position facing an outer peripheral portion, so that the etching rate in the central portion in the plane of the substrate 111 and the etching rate in the outer peripheral portion in the substrate plane 111 are caused to be different.