Etching method

Abstract

This invention provides an etching method for removing the natural oxide film formed on the surface of a silicon nitride film. The etching method includes: steps S13 and S14 (supplying hydrogen fluoride gas to the etched object followed by supplying free radicals to etch the surface oxide layer of the silicon nitride film); and repeating multiple cycles of supplying hydrogen fluoride gas to the etched object with the etched surface oxide layer followed by supplying free radicals (steps S16 to S18), thereby selectively etching the silicon nitride film relative to the silicon oxide film; the ratio of the amount of silicon nitride film etched to the amount of silicon oxide film etched is a selectivity ratio, and the first selectivity ratio of the processing conditions for etching the surface oxide layer is less than the second selectivity ratio of the processing conditions for selectively etching the silicon nitride film.