A plasma processing method can etch regions having different densities at the same etching rates. When etching with surface wave plasma, both of layers contain Si and N, a processing gas includes a hydro fluorocarbon gas, a rare gas, and an oxygen gas, and a high frequency bias potential is applied to a preset location at a side of a substrate. Further, a power per unit area of the substrate, which generates the high frequency bias potential, is set to be about 0 W/m2 or more to about 400 W/m2 or less.