Plasma processing method

A method of plasma processing in a processing chamber, comprising the steps of:

• plasma-etching a film comprising nitrogen atoms and silicon atoms, using a mixture of a hydrofluorocarbon gas and an oxygen gas, while supplying a radio frequency power to an object with the film to be processed so as to enable plasma-etching of the film, the radio frequency power having a first amplitude in a first period of plasma-etching and a second amplitude in a second period of plasma-etching of a plasma-etching cycle of the first and second periods which is repeated for the plasma-etching of the film;
• wherein the second amplitude of the second period of plasma-etching is smaller than the first amplitude of the first period of plasma-etching;
• and
• configuring a frequency of the plasma-etching cycle so that a thickness of deposition of a by-product generated during the first period of plasma-etching onto an inner wall surface of the processing chamber is no greater than 1 nm and a thickness of deposition of a by-product generated during the second period of plasma-etching onto the inner wall surface of the processing chamber is no greater than 1 nm.