ETCHING METHOD OF SILICON NITRIDE

PROBLEM TO BE SOLVED: To provide a method for etching silicon nitride capable of selectively etching silicon nitride without etching silicon oxide, and moreover capable of stably etching for a long period.SOLUTION: A method for etching silicon nitride containing an etchant containing phosphoric acid, fluoride silicon compound and water by using an etching device including an etching bath and an etchant regenerating bath comprises: (a) a step for etching the silicon nitride in the etching bath by continuously or intermittently supplying the phosphoric acid, silicon fluoride compound and water into the etching bath; (b) a step for continuously or intermittently draining the etchant in the etching bath out of the etching bath and moving it into the etchant regenerating bath; (c) a step for supplying hydrofluoric acid and/or hydrofluoric acid salt to the etchant that has been moved into the etchant regenerating bath and removing part of or all of silicon, water and fluorine; and (d) a step for returning liquid in the etchant regenerating bath obtained by removing part of or all of the silicon, water and fluorine as phosphoric acid to the step (a).