Patent ID: 8298435

Claim:
An etching method, comprising: etching a first plurality of silicon wafers in a first etchant, each silicon wafer of said first plurality of silicon wafers having a first silica layer of SiO 2 and a first silicon nitride layer of Si 3 N 4 deposited thereon, wherein said etching comprises dissolving a quantity of said SiO 2 from the first silica layer at a first etch rate of SiO 2 and a quantity of said Si 3 N 4 from the first silicon nitride layer at a first etch rate of Si 3 N 4 in said first etchant and a quantity of insoluble SiO 2 precipitates in said first echant in response to said dissolving; after said etching: determining the first etch rate of SiO 2 , determining the first etch rate of Si 3 N 4 , determining a ratio of the determined first etch rate of Si 3 N 4 to the determined first etch rate of SiO 2 from said first plurality of silicon wafers in said first etchant, and ascertaining that said determined ratio is less than a predetermined threshold; in response to said ascertaining, combining a portion of said first etchant with a second etchant to form a conditioned etchant, wherein said portion is essentially free of insoluble SiO 2 ; and after said combining, etching in said conditioned etchant a second plurality of silicon wafers having a second silica layer comprising SiO 2 and a second silicon nitride layer comprising Si 3 N 4 disposed thereon, wherein a ratio of a second etch rate of Si 3 N 4 to a second etch rate of SiO 2 from said second plurality of silicon wafers in said conditioned etchant is greater than said predetermined threshold.