Abstract: A substrate processing method for processing a substrate, on which a processing target layer, an intermediate layer, and a mask layer having an opening to expose a part of the intermediate layer are stacked in this order, includes a shrink etching step. In the shrink etching step, an opening width of the opening of the mask layer is reduced by depositing deposits on a sidewall surface thereof by a plasma generated from a gaseous mixture of depositive gas expressed by a general formula CxHyFz (x, y and z being positive integers) and SF6 gas. Also, there is formed in the intermediate layer an opening having an opening width corresponding to the reduced opening width of the opening of the mask layer by etching the intermediate layer.