Wastage determination method and plasma processing apparatus

An apparatus comprising:

• a chamber;
• a gas inlet configured to supply a fluorine containing gas and an oxygen containing gas into the chamber;
• a plasma forming unit configured to form a plasma from the fluorine containing gas and the oxygen containing gas supplied into the chamber;
• an optical emission spectrometer (OES) configured to measure light emission intensitites of fluorine radicals and oxygen radicals in the plasma;
• an expendable part disposed in the chamber;
• a storage unit in which a look-up table is stored, the look-up table including a relation between light emission intensitites of fluorine radicals and oxygen radicals and a wastage rate of the expendable part;
• and
• a processor configured to determine a wastage rate of the expendable part based on the measured light emission intensitites of fluorine radicals and oxygen radicals and the look-up table.