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

[Philipp Altpeter]

Thank you again for all your helpful advice!

I exposed the PMMA sample to the gold source using an emission current below the evaporation threshold to see whether secondary electrons or x-rays would cause similar damage. This was not the case (the color changed though)—even after a prolonged exposure.

I also deposited a 50 nm layer of platinum under conditions similar to those used for gold, and the resulting surface is very smooth.

Next, I plan to try a high-rate gold deposition, among other tests, and I’ll keep you updated on the results.

Thanks again for your valuable support!

Philipp

22.07.2025 17:48:06 Zhang, Hao <hao.zhang at uni-due.de>:

> Hello Philipp,
> 
> Which source do you use? Is from FerroTec? If is, then try to connect them to buy a magnet kit to deflect the secondary electron. This is a very common issue in e beam evaporation due to SE on photo resist surface. 
> Best wishes 
> 
> Hao
> 
> Von meinem iPhone gesendet
> 
>> Am 22.07.2025 um 16:19 schrieb Philipp Altpeter <philipp.altpeter at lmu.de>:
>> 
>> 
>> 
>> 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
>> 
>> 
>> 
>> <c8InTNtYBI4xtxk4.png>
>> 
>> -- 
>> 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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