Plasma etching method, control program and computer storage medium

A plasma etching method for plasma-etching a target substrate including at least a target film to be etched, an organic film, a Si-containing film, and a photoresist film patterned on the Si-containing film which are stacked in that order from bottom, the method comprising:

• a Si-containing film etching step of etching the Si-containing film by using the photoresist film as a first mask such that openings of the Si-containing film are formed;
• a first organic film etching step of etching a portion of the organic film thereby forming holes in the portion of the organic film;
• a treatment step of a treatment step of exposing, after the first organic film etching step, the Si-containing film and the organic film to a plasma of a rare gas such that a Si-containing protection film is formed on sidewalls of the holes;
• a second organic film etching step of etching, after the treatment step, the remaining portion of the organic film exposed through the openings;
• and
• a target film etching step of etching the target film by using the organic film as a second mask;
• and
• wherein, in the treatment step, the Si-containing film and the organic film are exposed to a plasma of an additive gas provided with the plasma of the rare gas, and the organic film and the Si-containing film are not etched by the plasma of the additive gas.