A single wafer etching apparatus and various methods implemented in the single wafer etching apparatus are disclosed. In an example, etching a silicon nitride layer in a single wafer etching apparatus includes: heating a phosphoric acid to a first temperature; heating a sulfuric acid to a second temperature; mixing the heated phosphoric acid and the heated sulfuric acid; heating the phosphoric acid/sulfuric acid mixture to a third temperature; and etching the silicon nitride layer with the heated phosphoric acid/sulfuric acid mixture.