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

[Demis D. John]

Perhaps try a higher dep rate - the theory being that heating (from
optical/other emission) is causing the PMMA to outgas, and long slow deps
may cause more heating.
Eg. Keep the Au dep to <1min total (you may need to adjust the soak steps
w/ shutter closed so it opens the shutter with ~0.5Å/sec and fairly fast
feedback loop).

Also, measure the thin-film stress of your Au - maybe it is high,
causing/exacerbating delamination.
However since your image also shows exploded bubbles on the PMMA only, I
suspect outgassing/bubbles more than just regular delamination due to
stress.

-- Demis (contact info <https://wiki.nanotech.ucsb.edu/wiki/Demis_D._John>)
*Reminder*: The NanoFab has a publications policy
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On Tue, Jul 22, 2025 at 07:23 Philipp Altpeter <philipp.altpeter at lmu.de>
wrote:

> 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. EfetovGeschwister-Scholl-Platz 1
> D-80539 München <https://www.google.com/maps/search/Geschwister-Scholl-Platz+1%0D%0AD-80539+M%C3%BCnchen?entry=gmail&source=g>
> T. +49 (0)89 2180-3733
>
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