[labnetwork] Bubble formation when e-beam evaporating Gold on PMMA

[Philipp Altpeter]

Dear all,

In recent months, we installed a new UHV e-beam evaporator and have 
since encountered significant issues with our standard lift-off process 
using 3 nm Chromium followed by 50 nm Gold. Specifically, we are 
observing the formation of large bubbles beneath the PMMA, which 
severely damage the PMMA layer (see image below). The rate is decently 
low, 0.6 A/s at around 40mA emission current, 10 kV. After around 30 nm 
of thickness, bubbles become clearly visible.

Interestingly, deposition on bare silicon, silicon dioxide, or other 
(photo)resists appears to proceed without problems.

We have already tried adjusting various parameters — including cooling 
conditions, beam wobbling, throw distance, and acceleration voltage. We 
also modified the PMMA baking protocol and tested PMMA dissolved in 
different solvents — all without success.

If anyone has experienced similar issues or has suggestions for 
troubleshooting, your input would be greatly appreciated.

Thank you in advance for your help!

Best regards,
Philipp


-- 
Philipp Altpeter
Fakultät für Physik der LMU
LS Prof. Efetov
Geschwister-Scholl-Platz 1
D-80539 München
T. +49 (0)89 2180-3733
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