Plasma processing method and apparatus, and storage medium

A plasma processing apparatus comprising:

• a mounting table having a cooling function, the mounting table being installed in a processing chamber and having a smaller size than a substrate;
• an electrostatic chuck installed on the mounting table, for electrostatically adsorbing the substrate;
• a power supply unit for applying a voltage to the electrostatic chuck;
• a thermally conductive gas supply unit for supplying a thermally conductive gas between a top surface of the mounting table and a bottom surface of the substrate, wherein after the substrate having thereon a resist mask is mounted on the mounting table and then electrostatically adsorbed by the electrostatic chuck, an etching process is performed on a surface of the substrate by using a plasma while the thermally conductive gas is supplied;
• and
• a control unit having a program including an instruction for stopping the thermally conductive gas supply of the thermally conductive gas supply unit after the etching process is completed, and an instruction for ashing the resist on the substrate by using a plasma of an ashing gas containing O2.