Buffered oxide etchant (BOE) is a wet etchant used in microfabrication. Its primary use is in etching thin films of silicon dioxide (SiO2) or silicon nitride (Si3N4). It is a mixture of a buffering agent such as ammonium fluoride (NH4F) and hydrofluoric acid (HF). Concentrated HF etches silicon dioxide too quickly for good process control and also peels photoresist used in lithographic patterning.