Nitrogen atom measurement method, the nitrogen atom measuring apparatus, plasma processing method, and a plasma processing apparatus

Provided is a method for measuring nitrogen atoms whereby nitrogen atom density is measured in real time at around atmospheric pressure. A method for measuring nitrogen atoms whereby nitrogen atom density is measured at around atmospheric pressure, which comprises: a procedure of mixing a portion in a definite amount of a nitrogen atom-containing gas generated from a nitrogen atom source with a definite amount of nitrogen monoxide gas with a known concentration in the downstream of the above-described nitrogen atom source; a procedure of, after the completion of the reaction between the above-described nitrogen atom-containing gas and the above-described nitrogen monoxide gas mixed therewith, measuring the nitrogen monoxide density and the nitrogen dioxide density; and a procedure of calculating the nitrogen atom density with the use of the relation that the nitrogen atom density corresponds to the difference obtained by subtracting the sum of the nitrogen monoxide concentration measured above and the nitrogen dioxide concentration measured above from the known concentration of the nitrogen monoxide gas as described above.