[labnetwork] Ebeam evaporation - arcing between features

[Houpu Li]

Hi Bob,
Thanks for sharing the case. I wonder if any conductive coating was used on
top of the resist?  When we do EBL on non-conductive substrates such as
SiO2 or Si3N4, because they lack the intrinsic conductivity as Si wafers
do, we typically need to use a layer of conductive coating on top, and use
conductive tape to ground it to the stage. The aim is to avoid the electron
accumulation on the chip during the e-beam writing, which is my suspicion
on why your user's sample would have arcings -  a lot of electrons go to
the sample and will accumulate if there is no way out, resulting in a
static charge that arcs later.
There is a commercial conductive coating product called "DisCharge" that
can be spin-coated on top. Before switching to DisCharge, we also tried
either a spin-coated layer of PEDOT:PSS or 10 nm of Cr layer, both can do
the job if coated properly and the feature size is not too small. Maybe the
user in your facility can give these a try if they want to do a
quick verification. PEDOT:PSS might have some wetting issues during spin
coating. DisCharge performs best overall and in theory will not affect
feature resolution.  The coating will go off when the developing and
lift-off happens and should not leave any residual afterward.
Hope this info helps.

Best
Houpu

--
----------------------------------------------
Houpu Li
Asst. Project Scientist.
Jack Baskin School of Engineering
UC Santa Cruz, California, USA
hli322 at ucsc.edu
houpuli0 at gmail.com
+1-4044229896

On Tue, May 21, 2024 at 3:43 PM Geil, Bob <bob.geil at unc.edu> wrote:

> Hello labnetwork,
>
>  I have a user that is fabricating some electrodes and has observed what
> appears to be arcing between the sharp points of the electrodes. Imagine
> features like this:  > < where the distance between them is 2um - 8um. The
> substrate is quartz. Fabrication approach is 1) ebeam lithography 2) ebeam
> evaporation and 3) lift-off.
>
> After EBL development, the electrode circuit is open, as intended
> After evaporation +lift-off, there is a line about few 100nms wide that is
> shorting the electrodes: >-<
> There is not a short between the electrodes with the 8um gap, however,
> there are some metal lines extending from the two sides:  >-  -<
>
> All of this suggests that arcing is occurring.  Has anyone observed this
> before and can you suggest ways to get around it?
>
> Thanks,
>   Bob
>
>
> Bob Geil, PhD
> Technical Director • CHANL
> Dept. of Chemistry • UNC-CH
> Chapel Hill, NC
>
>
>
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