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

[Chandan H B]

Thank you all for the feedback. I really appreciate the time and efforts
made to address this issue.

As most of you said, when the Au surface is wiped with a cleanroom
compatible lint free wipe, it easily comes off and Au looks pretty clean. With
that in mind, the primary suspect was carbon, but the question is, is it
originating from the Au slug itself or as Grant said is it from the
hydrocarbons from the chamber?

In the case of hydrocarbons, I should see the same black particle/layer on
any other material like Ti, Al, Pt, Ni, Cr etc., but I do not see any.
Considering if that happens, how is it attracting the hydrocarbons at the
very first place? Au can not be the first layer we coat as it needs an
adhesive layer like Cr or Ti. Let me know more information if anyone has
faced a similar kind.

Having said that, I went ahead with EDS and XPS to check the carbon
presence by giving out an Au pellet(99.999%). It did show 5~10 wt% of
presence on the surface scan and 0~0.5wt% upon depth profiling. Considering
these results, can source material undergo cleaning with IPA or DI water
followed by Plasma Cleaning?

This challenge is not new to many, so we look forward to hearing about how
others have mitigated it.

Thanks!
Chandan H B

On Fri, Sep 18, 2026 at 3:52 AM Ryan Rivers <rrivers at berkeley.edu> wrote:

> Hi Chandan,
>
> We use a tungsten crucible liner to avoid the problem entirely. Mo is also
> widely used as others have noted. I've had no issues with spitting from W
> crucibles myself. That's usually a matter of source material cleanliness
> and beam control. Spitting is almost always a function of your source
> pellets having some amount of residual carbon on them.
>
> The other thing you can do with W or Mo crucibles is heat the gold to a
> fully melted state with a liquid top (as opposed to a molten surface with a
> breached liquid where the beam is hitting) and allow it to just sit for a
> minute or two. If you're using a carbon spacer this is relatively trivial
> to do without evaporating any appreciable amount of gold. When you cool
> back down, all of the carbon in the melt will have floated up to the
> surface and you can simply wipe the melt clean with a techwipe until you
> get bright gold. You'll never see spitting out of the melt again until
> someone contaminates it some other way.
>
> -Ryan
>
> On Thu, Sep 17, 2026 at 4:42 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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>> labnetwork mailing list
>> labnetwork at mtl.mit.edu
>> https://mtl.mit.edu/mailman/listinfo.cgi/labnetwork
>>
>
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