[labnetwork] [EXTERNAL] Gold e-beam deposition - carbon contamination

[Clifford F Knollenberg]

It's the same story everywhere.  Our latest theory was the carbon was being absorbed from the junk molecules in the vacuum during the elevated temperatures of deposition (and then it nucleates into particles during cooling).  If it was diffusing in from the carbon/fabmate crucible we think we'd see erosion of the crucible walls over time (which we did not notice). The latest approach to minimizing carbon contamination was to pump down to the low 10-7 torr before depositing rather than starting your deposition in the high 10-7's (this sort of reinforces the above advice on keeping the chamber clean).  And keep other contaminants off your Au during handling (no finger prints, rinse with alcohol, etc.).

The cleaner thermal evaporations makes sense from my perspective. When I've done thermal evaporation, we loaded fresh gold every time (we did not reuse the source material), so the gold did not experience a pervious evaporation cycle where it would absorb junk from the vacuum.

I do like the idea of gettering with Tantalum.  Will have to look into that.

My two cents.  Hope you find a solution that works for you.

-Cliff


________________________________
From: labnetwork <labnetwork-bounces at mtl.mit.edu> on behalf of Demis D. John <demis at ucsb.edu>
Sent: Saturday, February 1, 2025 7:43 AM
To: Czwakiel, James <czwakj at rpi.edu>
Cc: Fab Network <labnetwork at mtl.mit.edu>
Subject: Re: [labnetwork] [EXTERNAL] Gold e-beam deposition - carbon contamination

Adding a tantalum pellet to the Au source will getter the carbon and reduce spitting.

I can’t quite find the original paper, but here are some web pages that reference it:
1)
https://compoundsemiconductor.net/article/116629/Tackling_the_foot#:~:text=concern.-,The%20combination%20of%20the%20crucible%20liner%20and%20tantalum%20%E2%80%98getters%E2%80%99%20looks%20like%20a%20win%2Dwin:%20the%20deposition%20rate%20increases%20while%20reducing%20gold%20spitting.,-But

2)
https://www.memsnet.org/memstalk/16896/#:~:text=look%20for%20a%20paperwritten%20in%20the%201970s%20that%20suggests%20adding%20a%20small%20piece%20of%20tantalum%20to%20yourgold.%20%20The%20Ta%20will%20not%20melt%20but%20it%20will%20control%20the%20spitting.


I don’t have measurements of carbon contamination with this - although we do this in our e-beam evaporators.

-- Demis (contact info<https://wiki.nanotech.ucsb.edu/wiki/Demis_D._John>)
Reminder: The NanoFab has a publications policy<https://wiki.nanotech.ucsb.edu/wiki/Frequently_Asked_Questions#Publications_acknowledging_the_Nanofab>


On Sat, Feb 1, 2025 at 05:17 Czwakiel, James <czwakj at rpi.edu<mailto:czwakj at rpi.edu>> wrote:
Youry

Once contamination is detected…. Clean clean clean
All metal covers removed and blasted and ultra sonically cleaned
Plus …. Make sure crucibles are not touched even with gloved hands….. always use tweezers


James Czwakiel

Semiconductor Equipment Engineer

[Image]



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From: labnetwork <labnetwork-bounces at mtl.mit.edu<mailto:labnetwork-bounces at mtl.mit.edu>> on behalf of Youry Borisenkov <yb2471 at columbia.edu<mailto:yb2471 at columbia.edu>>
Sent: Friday, January 31, 2025 11:59:09 AM
To: Fab Network <labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>>
Subject: [EXTERNAL][labnetwork] Gold e-beam deposition - carbon contamination


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Hi All and happy Friday,
I know it is a topic that has been discussed multiple times, however, I'm still lacking a solution that works and will appreciate you sharing your experience.

Currently we are using a Fabmate crucible, and getting some carbon contamination .
For clean Gold layers we use thermal evaporation. The films are good but it requires a lot of gold.

So far we tried using a Molybdenum crucible with and without a spacer. The issue with this approach was that eventually after some time, we get carbon contamination back. I believe it's present in the chamber and eventually a critical mass is built on top of the gold in the crucible, coming from the chamber.

Were anyone successful in overcoming carbon contamination in their e-beam deposition overtime?
What are the procedures you are following? Maybe cleaning more frequently?

--
Thank you,
Youry Borisenkov
CNI<https://cni.columbia.edu/columbia-university-clean-room>
Columbia University
CEPSR 1017, New York, NY, 10027, United States.
[https://sustainable.columbia.edu/sites/default/files/content/crown%20commuter%20badge_0.png]<https://sustainable.columbia.edu/crown-commuter>
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