Migrated from the old Google Sites wiki (Nov 2026). Text and numbers were carried over; photos and screenshots were not. If you have them, add them to assets/wiki/ and link them here. Check numbers against your own run before relying on them.
Temperature is the critical variable in DSE. If the sample overheats, the passivation layer burns off and you only get low-aspect-ratio etches. Everything below is about keeping the sample cool.
1. Helium cooling flow
- Recommended He flow: 2 to 4 sccm.
- Too high: excess He in the chamber changes the reaction rate.
- Too low: not enough cooling, and the sample overheats.
2. He backside pressure
- Match the setpoint to the sample. Heavy samples (a large piece on a carrier wafer) need higher pressure; light samples (thin wafers) need lower pressure.
- A setpoint of 4000 (tool units) has worked for most applications.
3. Backside cleanliness ⚠️ extremely important
Clean the wafer backside with acetone. Any debris leaves a small gap between wafer and chuck, which disturbs gas flow and cooling.
4. Thermal contact with Fomblin oil ⚠️ extremely important
Fomblin oil carries heat from the sample to the carrier.
- Put on a second pair of gloves.
- With a Q-tip, apply a thin layer of oil to the backside of the sample.
- Take off the outer gloves.
Keep oil off the carrier wafer. Oil contamination damages the chamber.
5. Standard recipe and etch rate
- Recipe: ZL_4inch DSE standard
- Etch rate: about 1 µm per cycle
- Check: 20 cycles produced an 18 µm trench, very close to expected.
6. What failure looks like
When He backside pressure was too low, the sample overheated and neighboring holes merged into one another.
Tips
- Avoid etching a full wafer if you can. Cooling is uneven across a full wafer, so some regions overheat and undercut.
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