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

[Grant Shao]

Hi Chandan,

Assuming it is carbon contamination (easy way to tell is if wipes off with IPA), we've had a lot fewer issues with carbon contamination after we switched from Fabmate to a tungsten crucible liner, but it sounds like you're already using a tungsten liner.

As per other folks' recommendations:

  *
We wipe down the slug with IPA using a foam swab when the chamber is vented. Be careful of anything that might leave fibers behind in the slug.
  *
We never touch anything without gloves on (though we're in the cleanroom, so we're already wearing gloves). That's generally what you should do for vacuum systems in general - wear clean gloves. We commonly double glove for easy replacing of the second glove if it gets dirtied.
  *
When you pump down the chamber, wait until the chamber gets to a decent low base pressure before you turn the ebeam on for the gold source. Your vacuum will have residual hydrocarbons, and the ebeam will actually attract the hydrocarbons to deposit onto the gold source. (Think carbon contamination from an SEM scan.) So the lower the base pressure you're at (our threshold typically is low e-6, if not in the e-7 torr range), the fewer hydrocarbons there are in the chamber to get attracted and deposited onto the gold source.

Minimizing carbon contamination can also help if you're getting resist blistering (especially with PMMA). From what I understand, the carbon scatters more electrons and you get more electron exposure to the resist, causing evolution of gases and resulting resist blistering.

Grant
________________________________
From: labnetwork <labnetwork-bounces at mtl.mit.edu> on behalf of Nadia Pervez <np65 at rice.edu>
Sent: Thursday, September 17, 2026 7:25 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
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np65 at rice.edu<mailto:np65 at rice.edu>
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