An etching method including: (a) preparing a substrate on a substrate support disposed in a chamber of a plasma processing apparatus, the substrate including a first film and a second film, the first film containing silicon and nitrogen, and the second film containing silicon and oxygen; (b) supplying a processing gas into the chamber; and (c) while the (b) is being executed, selectively etching the second film with respect to the first film, the (c) including (c1) forming a plasma by setting a power of a source RF signal having a first frequency to a first power, and supplying a first bias signal to the substrate support with a second power, the first bias signal having a frequency lower than the first frequency, and (c2) after the (c1), supplying the first bias signal to the substrate support with a third power higher than the second power.