|
|
| Line 83: |
Line 83: |
| So for a 10 wt% solution you will need 165 ml of KOH (50wt%) to 1 l of water. | | So for a 10 wt% solution you will need 165 ml of KOH (50wt%) to 1 l of water. |
|
| |
|
| | == Backside protection == |
|
| |
|
| KOH backside protection
| | '''It is possible to protect the backside of the wafer against the KOH etch using special wafer holder.''' |
| Nanolab has backside protection holders for the two baths KOH 2 and KOH 3 for 4” wafer, and it is possible to mount two wafers in one holder. The material is PEEK, which is suitable for nearly all etchants and you will find the holders by the KOH baths. The recommended space from the wafer edge to your pattern is 7 mm. The thickness of the wafer would typically be 350 μm and the wafer would typically be polished on both sides, however with the right gasket (contact wet chemistry) the holders can accommodate 500-525 μm wafers. In order to avoid differences in pressure between the backside of the wafer and the surrounding environment, the venting tubes should be filled with water. The holder is clamped around the wafers by screws, if these screws are tightened too much or too little, it will affect the etching result. For the KOH 2 bath we have another type of holder which is clamped around the wafer with clamps (it cannot be adjusted to another wafer thickness).
| |
| See more specific details about the screwed holders here, the holders we have at Nanolab is the Tandem4 type.
| |
|
| |
|
| ==Theory== | | ==Theory== |
