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

[John Shott]

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