[labnetwork] Troubleshooting defects in thick Al film (750 nm, 200 mm Si, e-beam evap)

[Carlos Gramajo]

Hi Bernhard,

Have you for EDX on the sample to see what it is?  Al and Silicon trade
places. Si and Al difuse into each other and continue until they have
completely exchanged places. I used this technique in past ti create P
doped Si due to some Al staying behind in the Si. There is a possibility
that if the sample  gets warm enough and the deposition takes long enough,
that you are seeing Si crystals coming out. If that checks out, then
increase your rate of evaporation  to limit the diffusion.

I cannot think of other possibilities other than some sort of
contamination, but that may be less likely.

Cheers,

Carlos Gramajo
Cleanroom Research Scientist
Shared Equipment Authority (SEA), Rice University
Cell: 713-470-8115; Office: 713-348-8243; cg70 at rice.edu

On Wed, Aug 20, 2025, 6:44 PM Bernhard Reineke <
bernhard.reineke at uni-paderborn.de> wrote:

> Dear Guoliang,
>
> Could this be electromigration?
>
> Best,
> Bernhard
>
>
>
> ------------------------------
> *Von:* labnetwork <labnetwork-bounces at mtl.mit.edu> im Auftrag von Wang
> Guoliang <guoliang.wang at silicon-austria.com>
> *Gesendet:* Mittwoch, 20. August 2025 21:31:46
> *An:* labnetwork at mtl.mit.edu
> *Betreff:* [labnetwork] Troubleshooting defects in thick Al film (750 nm,
> 200 mm Si, e-beam evap)
>
>
> Dear All from the Labnetwork community,
>
>
>
> Recently, our lab received a request to deposit a 750 nm aluminum film on
> a 200 mm Si substrate using e-beam evaporation. The deposition was carried
> out with an aluminum slug in a 40 cc water-cooled pocket. The process
> proceeded smoothly with stable rate, power, and pressure.
>
>
>
> However, upon initial microscopic inspection, the deposited aluminum film
> exhibited numerous black dots distributed across the entire wafer. We
> attempted several approaches to eliminate these defects, but so far have
> been unsuccessful.
>
>
>
> I am wondering if anyone has encountered similar issues when depositing
> thick aluminum films. Any insights or suggestions on how to address this
> problem would be greatly appreciated.
>
>
>
> Details of the evaporation:
>
>    - Deposition rate: 1 A/s
>    - Deposition power: ~20%
>    - Deposition pressure: ~5E-7 mbar
>    - Substrate cooling: No (Wafer were placed on a planar wafer holder)
>    - Throw distance: 1 m
>
>
>
> Approaches we have already tried:
>
>    - *AFM/SEM characterization* – The black dots varied in size, with the
>    largest reaching ~200 nm in diameter. Their morphology was pyramid-like,
>    featuring a central peak surrounded by some trenches.
>    - *EDX analysis* – The black dots were identified as aluminum.
>    - *FIB analysis *– There was no cavity inside the black dots.
>    - *Adhesion layer* – Adding a 75 nm Ti adhesion layer yielded no
>    improvement.
>    - *Different deposition rate at 5 A/s and 0.5 A/s* – Both yielded no
>    improvement.
>    - *Thickness variation* – Depositions at 200 nm, 400 nm, and 600 nm
>    were tested. Defects only appeared in the 600 nm Al layer. All wafers
>    exhibited similar film stress.
>    - *Pre-melted aluminum pellets* – Using a carbon crucible liner,
>    reduced deposition power, and the same rate resulted in an increased number
>    of black dots.
>    - *Multiple-stage deposition *– Depositing 400 nm with a liner,
>    pausing for 30 minutes, and then depositing an additional 350 nm yielded no
>    improvement.
>    - *Alternative substrates* – Depositions on Si substrates with thermal
>    oxide and on fused silica showed no improvement.
>
>
>
> Attached are the microscope image, AFM image, and SEM image for your
> reference.
>
>
>
> Thanks and best regards,
>
> Guoliang
>
>
>
> Guoliang​​
>
>
>
> Wang MSc
>
> Process Engineer
>
> SAL MicroFab
>
> Silicon Austria Labs GmbH
>
> High Tech Campus Villach - Europastraße 12
> <https://www.google.com/maps/search/Europastra%C3%9Fe+12?entry=gmail&source=g>
>
> A‑
>
> 9524
>
>
>
> Villach
>
> ,
>
> AT
>
> M: +4366488843743
>
> guoliang.wang at silicon-austria.com
>
>
>
>
>
>
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