The present invention provides a substrate processing method that can perform improved flattening and processing upon the formation of interconnects. The a substrate processing method includes a step of eliminating a level difference in a surface of a interconnect material to flatten a surface, a step of removing the interconnect material until the interconnect material present in the non-interconnect region of the substrate becomes a thin film or remains partly on a barrier material, a step of removing the interconnect material in the form of the thin film or remaining partly on the barrier material, a step of simultaneously removing the unnecessary interconnect material and the barrier material until the barrier material present in the non-interconnect region becomes a thin film or remains partly, and a step of removing the unnecessary interconnect material and the barrier material in the form of the thin film.