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

Thu Sep 17 17:51:36 EDT 2026

I have had good luck over here using a Mo liner with a graphite spacer beneath the crucible. We don’t really have any special cleaning procedures for the gold pellets when loading. We typically order 5N, 1/8" gold from Lesker, but with costs shooting up, we recently switched to 4N, 3 mm gold pellets from MSE. It seems to still be depositing well for us without any noticeable issues and was about 13% cheaper.
As David mentioned, we do see the gold wicking up the sides of the crucible, so we tend to keep it filled as close to half-full as possible to reduce the chances of the gold wicking over the sides and down into the pocket.

Kind regards,

Dylan Bartusiak
Facility/Lab Manager
COSINC Fabrication<https://www.colorado.edu/facility/cosinc/>
University of Colorado Boulder
303-492-2656 | LinkedIn<https://www.linkedin.com/in/dylanbartusiak/>

If your work used COSINC resources, please acknowledge:
COSINC, RRID:SCR_018985

________________________________
From: labnetwork <labnetwork-bounces at mtl.mit.edu> on behalf of David Barth <dsbarth at engineering.upenn.edu>
Sent: Thursday, September 17, 2026 9:58 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

[External email - use caution]

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<mailto: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<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
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Rice University
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