[labnetwork] Using CDA, rather than N2, as pump purge in Bosch-like processes?

[Lavallee, Guy P.]

John,
   I believe the issue with the Fluorine chemistries is the formation of HF if you ever have water in the CDA which then gets into the pumps.  The potential of creating this would obviously be dependent on how much unreacted fluorine would reach the pump as well as how reactive the effluents would be with water leading to the formation of HF.   

The other issue you have to think about besides water (which the pumps won't like either regardless of HF formation) would be the potential of oil being in the CDA.  This will be highly dependent on the type of CDA system you have at your facility.   

We have thought about changing from N2 to CDA as well but have been very hesitate due to the many unknowns and not wanting to risk it.  It would be interesting to hear others inputs.

Thanks,
Guy

Penn State University's Nanofabrication Laboratory
Lead Etch Engineer
Materials Research Institute
N-105 Millennium Science Complex (MSC Bldg)
University Park, PA 16802
Email: gpl107 at psu.edu
Phone: 814-865-9339
Cell: 814-777-0719


-----Original Message-----
From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of John Shott
Sent: Thursday, April 11, 2013 11:48 AM
To: Labnetwork
Subject: [labnetwork] Using CDA, rather than N2, as pump purge in Bosch-like processes?

Labnetwork Community:

Like many of you, I suspect, nitrogen is the single largest non-salary expense associated with running our facility.

Much of our nitrogen is used for pump purges in dry pumps.  Our average dry pump seems to use about 1 CFM (sorry, 25-30 SLM ...) which, at our pricing is about $4k per year.  For virtually all deposition processes using reactive gases and etch processes using corrosive gases, using nitrogen as a pump purge seems to be a firm requirement.  It is not as obvious, to me at least, that nitrogen is required in something like a SF6/fluorocarbon-based etch process like the switched Bosch processes that many of us run.  While I know that CDA isn't "free", in our case, the LN2 bill definitely comes out of our pocket whereas as CDA is a University supplied and supported building utility.

What experience, recommendations, or cautions can you offer related to switching our Bosch process tools from nitrogen to CDA pump purges?  If it matters, the dew point of our CDA is believed to be less than -40 C, but is not monitored continuously (and maybe not even monitored periodically ...).

Thanks for your consideration,

John




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