Patent ID: 7964108

Claim:
A method for regenerating etching solution, wherein the etching solution is a phosphoric acid aqueous solution used to etch a silicon nitride film within a treatment tank, comprising the steps of: extraction of the etching solution containing silicon compounds produced from said etching out of the treatment tank; and removal of said silicon compounds from said extracted etching solution by filtration, wherein said removal by filtration comprises supplying said extracted etching solution through a piping path comprising multiple filters connected to the piping path with valves, and switching flow of said extracted etching solution through said multiple filters alternately: (a) in series with switching so that each one of said multiple filters, in turn, is connected upstream of other of said multiple filters; and (b) through a selected one or more of said multiple filters, and wherein, after start up operation, said extracted etching solution is supplied at least to a first filter of said multiple filters comprising a filter element having already-deposited silicon compounds.