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

[Ryan Rivers]

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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