[labnetwork] N2 grade for blow guns

[John Shott]

Iulian:

First class is better than coach.  A Mercedes is better than what I drive.

But, I don't fly first class and I don't drive a Mercedes, so I guess 
that I'm going to voice an opinion that is somewhat contrary to that 
expressed by most of my esteemed colleagues who have weighed in.  You've 
heard from a number of the best university lab/facility managers 
representing a number of the best university research facilities and the 
best fab design people and the great majority say use UHP nitrogen.  
Also, many of those folks are in newer facilities whereas ours has been 
use for 25+ years.

However, in addition to some of the cost/quality/convenience issues that 
Tom Britton raised, I think it is important to ask what is the quality 
difference between your utility nitrogen and your UHP nitrogen.  If 
utility nitrogen has a standard meaning, I'm not sure that I know what 
it is.

In our case, both our utility (AKA 'house') nitrogen and our UHP 
nitrogen come out of the same (non-stainless) 9000 gallon cryogenic 
tank.  So, I believe that our utility nitrogen is "pretty good" 
quality.  Although we don't monitor it, I suspect that it is likely less 
than 1 ppm moisture content most of the time ... it certainly has been 
every time that we have had it tested, but we don't have either online 
or routine monitoring of our moisture levels.  The utility system also 
has high-quality inline particle filters just downstream of the 
vaporizers, but is routed in copper piping.  Our UHP nitrogen, however, 
goes through an additional set of Entegris Gatekeeper cartridge filters 
and then is routed in stainless.  In short, our utility nitrogen is, in 
my view, very good, but our UHP nitrogen is better.s

Like everyone, I suspect, we use UHP nitrogen for all of our process 
gases to furnaces, etchers, deposition tools, etc.
Utility nitrogen is used for pump purges and all of the other things 
that others have outlined.

However, all of our wet benches are only supplied with utility 
nitrogen.  Not only does that mean that our blow guns use utility 
nitrogen, but so do our SRDs ... the last thing that wafers will see 
before a furnace step.

While that likely sends shivers down the spines of many, that's the way 
that our facility is set up and it would now be expensive to change. 
Over the years, we've built a wide range of high-efficiency solar cells 
and high-energy physics particle detectors with finished carrier 
lifetime in the msec, if not 10s of msec, range.

So, while our utility nitrogen is still of pretty high quality, except 
for the fact that it is distributed in copper piping, that is what we 
use for blow guns and for our SRDs.  There are a lot of things to lay 
awake at night and worry about in operating facilities of this type, but 
in my case, using our utility nitrogen for these purposes is not one of 
them.  Of course, if utility nitrogen means something of greatly lower 
quality ... such as a nitrogen generator of the type used to fill tires 
with nitrogen at Costco ... then that is an entirely different matter.

Have a good weekend all,

John