In semiconductor industry equipment, fused silica glass is frequently used at high temperatures ranging from 1000℃ to 1300℃. Under such conditions, devitrification occurs due to the adhesion of impurities. The devitrified parts are the crystallized areas of the fused silica, and the transformation point of crystallization is 275℃. When the fused silica glass is cooled from high temperatures to this transformation temperature, the crystallized devitrified layer on the surface has a different coefficient of thermal expansion from the high-temperature α-phase and low-temperature β-phase of the fused silica glass itself. This results in an opaque, peeling appearance under rapid cooling; in more severe cases, cracking may occur.
To extend the service life of fused silica products, it is crucial to prevent the causes of devitrification. The main contaminants leading to devitrification include alkali metals, alkaline earth metals, sweat, saliva, oil stains, dust, etc. Even a contamination level of 0.1mg/cm² can cause a tenfold or even hundredfold increase in devitrification. Therefore, to prevent these contaminants from adhering to the fused silica surface, direct handling with bare hands should be avoided. Additionally, thorough cleaning must be performed prior to high-temperature operations to ensure the surface cleanliness of the fused silica.
General cleaning of fused silica follows a set procedure: first, rinse the surface with pure water, then immerse it in an acid bath for a specified period, remove it, rinse again with pure water, and finally air-dry it. The types of acid solutions are as follows:
| Category/Item | Concentration | Time |
|---|---|---|
| Hydrofluoric Acid (HF) | 47.0% ~ 52.0% | 1 ~ 2 minutes |
| Hydrofluoric Acid (HF) | 5.0% ~ 10% | 10 ~ 15 minutes |
| Hydrofluoric Acid + Nitric Acid | 50% + 65% | 10 ~ 15 minutes |
| Hydrofluoric Acid + Sulfuric Acid | 50% + 65% | 10 ~ 15 minutes |