Etching method for silicon nitride and production method for semiconductor element

An etching method for silicon nitride, comprising:

• performing an etching step in which an etching object containing silicon nitride uses an etching gas, to etch the silicon nitride contained in the etching object under a pressure of 1 Pa to 80 kPa without using plasma,
• wherein the etching gas consists of
• i) a halogen fluoride only,
• ii) a halogen fluoride and hydrogen fluoride, or
• iii) a halogen fluoride, hydrogen fluoride and an inert gas,
• wherein the halogen fluoride is at least one selected from among bromine trifluoride, bromine pentafluoride, iodine pentafluoride, and iodine heptafluoride,
• wherein a content of the hydrogen fluoride contained in the etching gas is below 100 ppm by volume,
• the etching object contains the silicon nitride and an etching-resistant material configured to suppress etching of the silicon nitride by the etching gas, and
• the silicon nitride of the etching object is selectively etched by the etching gas.