[labnetwork] Johnson Matthey H2 Purifier

[Travis Wade]

Hi Rachel,

These purifiers are conducive to easy troubleshooting.  The Pd purifier is
designed to only pass hydrogen when at high temperature, so to check for
leakage, allow the purifier to cool to ambient (under inert gas) and try to
flow gas (any gas) through it.  Any flow at room temperature indicates a
cracked membrane and a replacement purifier cell will be required.  I
suspect this will reveal your issue.

If no flow is possible when the membrane is cool, the entire chamber should
be leakchecked, with an emphasis on process gas lines and valves.

Methane is a likely source of low nitrogen concentrations.  Methane
purifiers exist, and thankfully, are less expensive than hydrogen
purifiers.  However, their failures are not so simple to diagnose as
your HP-25.

For extremely low nitrogen concentrations in your process chamber, you may
find that it is always desirable to flow hydrogen for a while before
igniting the plasma.

Feel free to reach out to me directly if you have further questions.

Best regards,

Travis
----------------------------------------------
Travis Wade, Ph.D.
Evolve Diamonds LLC
Ph. (978) 434-2283
www.EvolveDiamonds.com

On Wed, Oct 20, 2021 at 12:12 PM Rachel Schoeppner <rlschoeppner at ucsb.edu>
wrote:

> Good Morning,
>
>
> We have a Johnson Matthey HP-25 hydrogen purifier that we suspect is not
> functioning properly. In its idle state it is kept under low UHP N2 flow,
> and we think that some of this is getting through the purifier into the
> lines of our CVD. At the start of deposition when we start H2 flow and
> ignite the initial plasma we see an unexpected peak in nitrogen (verified
> both in the emission spectrum of the plasma as well as nitrogen that is
> incorporated in the epitaxial film as measured with SIMS). When we flow the
> hydrogen gas through the growth chamber for ~20 min before deposition, no
> nitrogen peak is observed, suggesting that it is coming in as an initial
> “plug” through the purifier at the very beginning that can be flushed
> through. There is also a low amount of background nitrogen throughout the
> deposition (this could be an impurity in the methane, but I am not sure how
> likely that is).
>
> We have leak checked the line running from the purifier to the CVD chamber
> and cannot detect any leaks that might be causing the initial nitrogen
> spike.
>
> We are wondering if anyone has experience with these purifiers or ideas on
> how to diagnose their proper functionality. If it is letting unwanted
> species through, then what would be our options for fixing or replacing it?
>
>
> Thank you!
>
>
> Rachel
>
> —
>
> *Rachel Schoeppner, Ph.D*
>
> Nanostructure Cleanroom Facility Manager
> California NanoSystems Institute (CNSI)
> University of California, Santa Barbara
> rlschoeppner at ucsb.edu
> rachel at cnsi.ucsb.edu
> (805)893-2296
>
>
>
>
>
>
>
>
>
>
>
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