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

[David Barth]

Hi Chandan,

I generally agree with the previous comments, but also note this paper
<http://csmantech.org/wp-content/acfrcwduploads/field_5e8cddf5ddd10/post_2621/122.pdf>
which found significantly less spitting from Au deposited from Mo crucibles
vs W.

One other note is that Au wets W and Mo much better than carbon, so you'll
find that the molten metal likes to creep up the sides of the crucible,
which can be inconvenient.

Best,
David Barth
QNF, Singh Center for Nanotechnology
University of Pennsylvania

On Thu, Sep 17, 2026 at 11:55 AM Nadia Pervez <np65 at rice.edu> wrote:

> 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
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