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

[McCabe, Lauren]

Hi Chandan,

We swapped to a molybdenum liner for our gold sources and haven't had issues with a carbon film forming on top since. The gold does like to migrate out of the moly liner, so we will use a double liner (a 7cc liner sitting in a 15cc liner that fits our pocket size) to keep it from migrating into the system and replace the source every year or so.

Thanks,


[photo]

Lauren McCabe, PhD
Assistant Director, Yale University Cleanroom

+1 (609) 902-3834

research.yale.edu/cores/cleanroom<https://research.yale.edu/cores/cleanroom>

lauren.mccabe at yale.edu<mailto:lauren.mccabe at yale.edu>

Becton Engineering and Applied Science Center (BCT), Room 527<https://maps.google.com/?q=Becton%20Engineering%20and%20Applied%20Science%20Center%20(BCT),%20Room%20527>

15 Prospect Street, New Haven, CT06511

[linkedin]<https://www.linkedin.com/in/lauren-mccabe-525a2476/>

________________________________
From: labnetwork <labnetwork-bounces at mtl.mit.edu> on behalf of Nadia Pervez <np65 at rice.edu>
Sent: Thursday, September 17, 2026 10:25 AM
To: Chandan H B <chandanachar95 at gmail.com>
Cc: labnetwork at mtl.mit.edu <labnetwork at mtl.mit.edu>
Subject: Re: [labnetwork] Black Layer Formation During Au E-Beam Evaporation

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<mailto: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<mailto:np65 at rice.edu>
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