Abstract: The present invention provides a regeneration process of the etching solution for the silicon nitride film, applying phosphoric acid aqueous solution, wherein multiple numbers of filters are connected to the piping path of etching solution extracted from the etching tank by switching alternately in parallel or in series; in both cases that said multiple numbers of filters are connected in parallel or in series, said extracted etching solution being supplied to a filter with a filter element of a high silicon removal rate of silicon compounds with already deposited silicon compounds, thus maintaining a high silicon removal rate of silicon compounds.

Abstract: Disclosed is equipment for measuring a silicon concentration in a phosphoric acid solution under use as an etching solution during operation of a semiconductor substrate processing system. The equipment is provided with at least a reaction tank and a concentration-measuring tank. The reaction tank includes a reaction unit for adding hydrofluoric acid to a predetermined constant amount of the phosphoric acid solution drawn out of the semiconductor substrate processing system to form a silicon fluoride compound and then causing the silicon fluoride compound to evaporate. The concentration-measuring tank comprises a hydrolysis unit for bubbling the silicon fluoride compound, which has evaporated from the reaction tank, through deionized water to hydrolyze the silicon fluoride compound and a measurement unit for determining a change rate of silicon concentration in the deionized water subsequent to the bubbling.