Buffered Oxide Etch

Buffered oxide etch is a mixture of NH₄F and HF used to isotropically etch SiO₂ or Si3N4 in silicon microfabrication
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an etching solution containing hydrofluoric acid, HF, and ammonium fluoride, NH3F. The hydrofluoric acid etches silicon dioxide and the ammonium fluoride raises the solution pH reducing the attack rate of the solution on photoresist.