DRY ETCHING METHOD

A dry etching method according to the present invention includes etching silicon nitride by bringing a mixed gas containing hydrogen fluoride and a fluorine-containing carboxylic acid into contact with the silicon nitride in a plasma-less process at a temperature lower than 100° C. Preferably, the amount of the fluorine-containing carboxylic acid contained is 0.01 vol % or more based on the total amount of the hydrogen fluoride and the fluorine-containing carboxylic acid. Examples of the fluorine-containing carboxylic acid are monofluoroacetic acid, difluoroacetic acid, trifluoroacetic acid, difluoropropionic acid, pentafluoropropionic acid, pentafluorobutyric acid and the like. This dry etching method enables etching of the silicon nitride at a high etching rate and shows a high selectivity ratio of the silicon nitride to silicon oxide and polycrystalline silicon while preventing damage to the silicon oxide.