[labnetwork] Black Layer Formation During Au E-Beam Evaporation

[Nadia Pervez]

Hi Chandan,

We get a layer of carbon on the surface of our Au slug, which could be what
you are seeing. We use a fabmate crucible liner. Many of our users are
depositing Au for liftoff and/or on polymer substrates, and we also have
some users mounting samples with kapton tape or even using kapton tape
stencils. The chamber has an excellent base pressure (can go down to 10-9s).

These are our practices:
- We wipe down both the slug and the liner with IPA every time we change
the crystal (it is a load locked system with most of our users depositing
Au; we typically vent for crystal changes 3x as often as adding source
material), after which point we do not handle either directly with gloves
- We also occasionally plasma clean the Au slug if it doesn't look clean
with just the IPA
- When we add material we wash the Au pellets with IPA before loading them
- We buy our pellets from Lesker, 99.999% 1/8" diameter x 1/8" long

We started these practices after having problems with Au spitting. We also
changed the fabmate liner at that time (we had used the same one for many
years). Back when we had the spitting problem we were going to perform
ToF-SIMS but never got around to it. At that time Demis John suggested
adding Ta pellets for gettering, but we ended up not needing them.

Thanks,
Nadia

On Thu, Sep 17, 2026 at 6:46 AM Chandan H B <chandanachar95 at gmail.com>
wrote:

> Dear LabNetwork Community,
>
> We would like to seek inputs from cleanroom/fab facility managers and
> process owners regarding an issue observed during *Au deposition in our
> E-Beam Evaporators*.
>
> We have observed the formation of *black/dark layer on the Au charge
> after a few melt cycles*. The observation occurs during repeated melting
> of Au in a tungsten liner/crucible. We are currently investigating whether
> this could be related to *material surface contamination, crucible/liner
> condition, outgassing, chamber history, or the Au pre-cleaning/conditioning
> procedure*.
>
> We would appreciate your experience on the following:
>
>    - Have you observed *black/dark spots or a black layer forming on Au
>    during repeated E-beam melting/evaporation*?
>    - What *Au purity and material form* do you use?
>    - Do you perform any *cleaning/degreasing of the Au charge before
>    loading*? If yes, what procedure?
>    - Do you follow a specific *crucible/liner cleaning or replacement
>    procedure*?
>    - If you have identified a *root cause or corrective action* for a
>    similar observation, any details would be highly appreciated.
>
> Our objective is to compare practices across facilities and determine
> whether this is a *material-handling, source/liner, chamber-condition, or
> process-related phenomenon*.
> Any suggestions/inputs are highly appreciated.
> Thanks in advance!
>
> Regards,
> CHANDAN H B
> THIN FILMS ENGINEER
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-- 
Nadia Pervez, PhD
Cleanroom Research Scientist
Shared Equipment Authority (SEA)
Rice University
6100 Main St, MS-686
Houston, TX 77005
np65 at rice.edu
Office: SST-017, 713-348-5069 <(713)%20348-5069>
Cell: 805-284-1193 <(805)%20284-1193>
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