Etching method

An etching method comprising:

• a) placing a substrate on a stage in a chamber, the substrate having a silicon oxide film and a patterned mask disposed on the silicon oxide film;
• b) providing a first phase including
• supplying a first gas including a first fluorocarbon gas into the chamber,
• forming a first plasma from the first gas in the chamber, and
• exposing the substrate to the first plasma to etch the silicon oxide film, thereby causing a recess to be formed into the silicon oxide film through the patterned mask and causing a reaction product to be deposited on the recess and the patterned mask in the vicinity of an opening of the recess;
• c) providing a second phase including
• supplying a second gas including an oxygen gas into the chamber,
• forming a second plasma from the second gas in the chamber by applying a first high frequency electric power and a second high frequency electric power to the stage, the first high frequency electric power being different from the second high frequency electric power, and
• exposing the substrate to the second plasma to etch the patterned mask while removing the reaction product;
• and
• d) providing a third phase including
• supplying a third gas including a second fluorocarbon gas into the chamber, the second fluorocarbon gas being different from the first fluorocarbon gas,
• forming a third plasma from the third gas in the chamber, and
• exposing the substrate to the third plasma to etch the silicon oxide film in the vicinity of the opening.