[labnetwork] Carbon contamination from Ar

[Kevin McPeak]

Dear Colleagues,

In my lab at LSU we are interested in evaporating Au under high Ar
pressures, 10 - 50 mTorr. We are using Ar 5.0 purity (99.999%), which
has a THC of 1 ppm.

Our procedure is such:

1). Pump chamber down to low -7 Torr range
2). Inject 30 SCCM Ar and throttle gate valve to the desired pressure
(say 50 mTorr)
3). Increase power to Tungsten boat till Au pellets evaporate

When we vent the chamber we notice a lot of carbon deposition near the
outlet of the Ar line (see attached image). We have a THC of 1 ppm in
the Ar tank. We also tried hooking up a GP-100 gas purifier from RD
Mathis. Unfortunately, that didn't solve the problem, still lots of
carbon deposition in the chamber. The GP-100 is currently connected
upstream from the MFC. I am using SS tubes with all VCR fittings
(total length 6 ft). We could move the GP-100 closer to the chamber,
post-MFC.

Based on the photo I think it is pretty clear that the carbon is
coming from the Ar. So my current thought is that either I have a leak
in my tubes post GP-100 or I need to flame bake the lines (I have not
done this). I am trying to get access to an RGA to investigate this
more quantitatively. I do have access to a He checker so I could try
pumping on the Ar lines.

Have any of you seen Carbon contamination like this before when doing
high-pressure evap (I know that is not a normal thing)? I am curious
what people think. Thanks!

Regards,
Kevin

-- 
Kevin M. McPeak
Assistant Professor
Louisiana State University
Dept. of Chemical Engineering
110 Chemical Engineering Bldg Room 324
S. Stadium Drive
Baton Rouge, LA  70803
email: kmcpeak at lsu.edu
phone: 225-578-0058
-------------- next part --------------
A non-text attachment was scrubbed...
Name: mcpeak_PVD_Ar_Carbon_Contaminants.png
Type: image/png
Size: 534998 bytes
Desc: not available
URL: <https://mtl.mit.edu/pipermail/labnetwork/attachments/20171027/e3f76f9b/attachment.png>