Patent ID: 7323421

Claim:
An etching process for etching silicon from the surface of a silicon wafer, the process comprising contacting the silicon wafer with a caustic etchant in an etching apparatus to remove a layer of silicon from the surface of the silicon wafer, the layer having a thickness of at least about 2.5 μm, the caustic etchant comprising, upon initiation of said contact, water, at least about 40% by weight of a hydroxide ion source, and a metal chelating agent to sequester metal ion impurities in the caustic etchant from the surface of the silicon wafer, wherein the chelating agent is selected from the group consisting of ethylenediaminetetraacetic acid, diethylenetriaminepentacetic acid, glycolic acid, glycine (oxidase), dimethylgloxime, iminodisuccinic acid, nitrilotriacetic acid, and mixtures thereof, wherein before initiating said contact, the concentration of free metal ions in the caustic etchant is less than about 1 ppb, and wherein the concentration of free metal ion impurities in the caustic etchant is maintained at a value of less than about 100 ppb after initiating said contact.