Etching is a technique to create patterns in glass and silicon substrates by chemically or physically removing selected parts from the surface of the wafer. The removal of material can be limited to a specific layer, but can also consist of a larger portion of material. Etching can be performed using wet or dry techniques, depending on the substrate material and the desired geometry of the etched structure. In wet etching, liquid chemicals are used, where dry etching makes use of gases or plasmas as etchants. Powder blasting is another etching method for silicon and glass patterning.
Dry etching
Deep Reactive Ion Etching (DRIE or plasma etching) is a dry etching technique to create high density and high aspect ratio structures in glass and silicon substrates. In (D)RIE etching, sections of the substrate are removed as a result of a bombardment of the material with ions. Both etching with steep sidewalls (anisotropic etching) as well as with rounded sidewalls (isotropic etching) is possible, with depths varying between 1 µm cavities and complete wafer-through holes.
DRIE of silicon
Silicon structures with high aspect ratios can be achieved using the DRIE Bosch process. This process alternates every few seconds between three consecutive steps:
- Silicon etching, using an etch gas, eg. SF6.
- Passivation, using a passivation gas, eg. C4F8. A thin passivation film is deposited on the surface of the sidewalls and bottom of the trench to stop the etching process.
- Bottom film etching. In order to perform the next silicon etching step and create a deeper structure, the passivation film at the bottom of the trench has to be opened up. The vertical sidewall remains untouched and stays passivated and protected.
These sequences of etching, passivating, and opening up are repeated until the chosen etching-depth has been reached or until a complete through-hole has been created.
For DRIE of silicon, Micronit can offer the following:
- Aspect ratio up to 1:50
- Through-wafer etching
- Multiple depth etching
- Variable taper angle of the sidewalls
- Selectively stopping on silicon oxide or nitride membranes
- Aligned front and backside etching
DRIE of glass
Micronit is one of the few companies able to use the DRIE method in glass substrates. With this unique technique, Micronit is able to create high aspect ratio structures in glass substrates. Not only the pure quartz glass can be dry-etched using this technology, but also less costly glass such as BF33® or D263®. Glass wafers of Borofloat (BF33®) can be anodically bonded to silicon. This way, complex and highly integrated technologies for multidisciplinary applications can be fabricated.
For DRIE of glass, Micronit can offer the following:
- Aspect ratio 1:3
- Depths up to 80 µm
- Multiple depths
- Variable steepness of the sidewalls
- Positive taper
- Aligned front and backside etching