Buffered oxide etch

Buffered oxide etch (BOE), also known as buffered HF or BHF, is a wet <a href="/facts/Etching_(microfabrication)/kPa01dgL">etchant</a> used in <a href="/facts/Microfabrication/TzGo63pr">microfabrication</a>. It is a mixture of a <a href="/facts/Buffering_agent/zrLz9eaa">buffering agent</a>, such as <a href="/facts/Ammonium_fluoride/uVcvFh2b">ammonium fluoride</a> NH4F, and <a href="/facts/Hydrofluoric_acid/wdXqu4bE">hydrofluoric acid</a> (HF). Its primary use is in etching <a href="/facts/Thin_film/nSeoUT4Q">thin films</a> of <a href="/facts/Silicon_nitride/58X9QPQJ">silicon nitride</a> (Si3N4) or <a href="/facts/Silicon_dioxide/A3WILp6J">silicon dioxide</a> (SiO2), by the reaction:
SiO2 + 4HF + 2NH4F → (NH4)2SiF6 + 2H2O
Concentrated HF (typically 49% HF in water) etches silicon dioxide too quickly for good <a href="/facts/Process_control/tmjQhchm">process control</a> and also peels photoresist used in <a href="/facts/Photolithographic/FTHsauvy">photolithographic</a> patterning. Buffered oxide etch is commonly used for more controllable etching. Buffering HF with NH4F results in a solution with a more stable pH; thus, more stable concentrations of HF and HF−2, and a more stable etch rate.
Some oxides produce insoluble products in HF solutions. Thus, HCl may be added to BHF solutions in order to dissolve these insoluble products and produce a higher quality etch.

Buffered oxide etch open-in-new

Buffered oxide etch