In microelectronic assembly fabrication applications, wet etching of silicon dioxide is typically carried out using a hydrofluoric acid solution. The silicon dioxide can react with room temperature hydrofluoric acid solution, but does not etch silicon substrate and complex silicon. The reaction is as follows:

SiO2 + 6HF = H2 + SiF6 + 2H2O

As the etching rate of hydrofluoric acid on silicon dioxide is very high, it is difficult to control in the process, so in practice are used after dilution of hydrofluoric acid solution, or the addition of ammonium fluoride as a buffer mixture, to etch the silicon dioxide. The addition of ammonium fluoride can avoid the consumption of fluoride ions to maintain a stable etch rate. Without the addition of buffer hydrofluoric acid etching solution often cause the stripping of photoresist. The typical etch rate of BOE (Buffer Oxide Etcher) (6: 1 by volume of ammonium fluoride (40%) versus hydrofluoric acid (49%)) for high temperature growth oxide is about 1000? /min.

In the semiconductor manufacturing process, the formation of silica can be divided into thermal oxidation and chemical vapor deposition, etc.; and the use of silica in addition to pure silica, there are impurities such as BPSG silicon dioxide. However, the etch rate of the hydrofluoric acid solutions for these silicas will vary depending on the composition or structure of these differently grown or different components of silica. However, in general, high temperature thermal growth of the oxide layer than the chemical vapor deposition of the oxide layer etching rate is slow, because its composition is more compact.