Method of etching film and plasma processing apparatus

A plasma processing apparatus, comprising:

• a chamber;
• a substrate supporting mechanism provided within the chamber;
• a gas supply configured to supply a gas into the chamber;
• a radio frequency power supply configured to generate a radio frequency power to form plasma from the gas within the chamber;
• and
• a controller configured to control the gas supply and the radio frequency power supply,
• wherein the controller is configured to control the gas supply and the radio frequency power supply to perform a main etching on a film of a substrate, the substrate including an underlying region, the film provided on the underlying region and a mask provided on the film, the mask being patterned, and the main etching exposing at least a part of the underlying region and forming a side wall surface in a tapered shape on the film, wherein the substrate further includes a first region and a second region, and a pattern of the mask in the first region is formed more densely than a pattern of the mask in the second region,
• the controller is further configured to control the gas supply and the radio frequency power supply to form a protective layer, which is made of a different material from the film, on at least a side wall surface of the mask and the side wall surface of the film after the main etching,
• the controller is further configured to control the gas supply and the radio frequency power supply to remove a portion of the protective layer formed on the side wall surface of the film while remaining a portion of the protective layer formed on the side wall surface of the mask, and
• the controller is further configured to control the gas supply and the radio frequency power supply to perform an over-etching on the film on the substrate after the protective layer is formed.