[labnetwork] Aluminum contamination concerns in PVD

[Matthew Moneck]

Hi Mcolisi,



Given the set of materials you current deposit in the tool, there is a
concern.  Both Au and Pt can form a brittle, high resistance intermetallic
compound with Al, especially under heat.  In the case of Au, it even has
the nickname “purple plague,” due to it’s characteristic purple color.
Because of the brittle nature of these compounds we have found that use of
Al and Au or Al and Pt in a system together can result in flaking and
potenial contamination if not managed properly.  In particular, we have
seen “purple plague” form on shields, holders, etc. when users evaporate Au
and Al back to back.  This may not initially contaminate the pockets or
samples, but it can lead to premature flaking of materials in the chamber
between maintenance cycles.  In turn, the flakes can then potentially
contaminate pockets of material.



All of the above said, I do believe it can be managed.  In our case, we
have enough requests to do Al and Au in the same chamber that we have
decided to adapt and allow it.  Our solution has been to deposit Ti before
and after any Al run.  This has helped to mitigate the issues, but I still
suggest checking and cleaning shields, holders, etc. regularly.



Best Regards,

Matt



--

*Matthew T. Moneck, Ph.D*

Executive Director, Claire & John Bertucci Nanotechnology Laboratory

Electrical & Computer Engineering | Carnegie Mellon University

5000 Forbes Avenue, Pittsburgh, PA 15213-3890

Phone:  412-268-5430

ece.cmu.edu <http://www.ece.cmu.edu/>

nanofab.ece.cmu.edu <http://www.nanofab.ece.cmu.edu/>



*From:* labnetwork <labnetwork-bounces at mtl.mit.edu> *On Behalf Of *Mcolisi
Dlamini
*Sent:* Tuesday, November 22, 2022 7:01 PM
*To:* labnetwork at mtl.mit.edu
*Subject:* [labnetwork] Aluminum contamination concerns in PVD



Dear lab network:



We are wondering if there are any contamination issues (or potential
contamination) from adding and evaporating aluminum in our PVD system. We
understand that there will be physical contamination from flakes and metal
buildup. However, we are not sure whether Al will contaminate and affect
other deposition processes. Our PVD is non-CMOS clean grade and
is currently qualified to evaporate Au, Ti, Pd, and Pt on the e-beam hearth
and only Cr has been used so far on the thermal source.



The key question we have is whether aluminum has a risk of contaminating
the tool and affecting other processes? Our PVD is used for basic
metallization needs including for lift-off and IC chip fabrication.



We reviewed previous exchanges on this network but they mostly focused on
gold contamination in vacuum systems. Notably they do emphasize that tools
should be classified based on cleanliness, eg. CMOS clean, semi-clean and
the Au friendly category. This is something we will definitely keep in mind
moving forward. (Gold contamination lab network thread:
https://mtl.mit.edu/pipermail/labnetwork/2015-June/001867.html). Additionally,
there is mention of Aluminum carbide contamination when Al is evaporated
via e-beam, but we gathered that this can be mitigated by evaporating at
relatively low powers.



We will appreciate your insights on this topic specific to Al contamination
as well as contamination in metal evaporators in general.



Thank you,

-Mcolisi





*Mcolisi Dlamini*

4D LABS <http://www.4dlabs.ca>

Simon Fraser University

P: 778.782.9322
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