Method for treatment of treated substrate, and plasma treatment device

The present invention in one aspect provides a method for treatment of a treated substrate. The method includes: (a) a step in which a treated substrate is supported on a support stage disposed inside a treatment container, and in this state, a resist mask is exposed to an activated species of hydrogen generated by exciting a plasma of a hydrogen-containing gas inside the treatment container; and (b) a step following the aforementioned step of exposing the resist mask to the activated species of hydrogen, in which a plasma of an etchant gas is excited inside the treatment container, and a hard mask layer is etched. The plasma is excited by applying high-frequency power for plasma excitation to an upper electrode. According to this method, the distance between the upper electrode and the support stage during the aforementioned step (b) of etching the hard mask layer is set to a greater distance than that between the upper electrode and the support stage during the aforementioned step (a) of exposing the resist mask to the activated species of hydrogen.