Regeneration method of etching solution, an etching method and an etching system

1. 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.

2. A regenerating method according to claim 1 , further comprising the steps of:

switching the flow of said extracted etching solution so that said multiple filters are connected to the piping path in series so that said flow is first supplied to a second filter of said multiple filters comprising a filter element having no deposit of silicon compounds, said second filter being upstream of said first filter on said piping path;

continuing to supply the flow of said extracted etching solution through the second filter and the first filter in series until silicon compounds deposit and accumulate on the filter element of said second filter; and

then switching the flow of said extracted etching solution to supply the flow only to said second filter and at the same time removing said first filter for rinsing to remove deposited silicon compounds.

3. A regenerating method according to claim 2 , wherein a time during which said multiple filters are connected to the piping path in series is a time corresponding to one tenth to one half of the maximum amount of accumulation until clogging of the filter with silicon compounds occurs.

4. A method for etching, comprising:

an etching process of etching a silicon nitride film using an etching solution comprising phosphoric acid aqueous solution in a treatment tank;

a circulation filtration process in which etching solution containing silicon compounds produced in said etching process is extracted out of the treatment tank, filtrated and circulated to the treatment tank;

a phosphoric acid aqueous solution regeneration process in which a portion of the etching solution is extracted out of said circulation filtration process, water is added to said portion of extracted etching solution, and silicon compounds crystallized in said extracted etching solution are filtered for removal, causing said etching solution to be regenerated, wherein said filtering for removal 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, to yield regenerated etching solution, and

a process of returning said regenerated etching solution to said treatment tank of said etching process.