Buffered Oxide Etch
Buffered Oxide Etch is a chemical that is used for etching in a micro fabrication setting. It is a mixture of a buffering agent such as ammonium fluoride and hydrofluoric acid. This mixture is usually in the etching of silicon dioxide and silicon nitride. It is a more controlled etch than hydrofluoric acid itself. The pure acid peels photoresist which is commonly used in lithographic patterning. This makes the buffered oxide the best etching solution.
The common mixture is a 6:1 ratio of ammonium fluoride in water to hydrofluoric acid in water. This solution mix will etch at approximately two nano meters per second at a temperature of twenty five degrees Celsius. Raising the temperature will increase the rate at which the etching happens. It is also important to continually mix the solution as this will make a homogeneous solution and will provide a smooth even etch for the product.