[labnetwork] Venting Tools with Building Nitrogen

[John Shott]

Milan:

You will likely get a wide range of opinions on this issue. However, a 
lot will depend on the quality of the gas that is coming out of your 
system.  Telling you what I have may be irrelevant if your gas is either 
much better or much worse than what we have.

We (the Stanford Nanofabrication Facility) have a single, stainless 
steel 9000 gallon LN2 tank that supplies both our copper-piped house 
nitrogen system and our stainless-routed UHP nitrogen system.  Aside 
from the piping, the other thing that differentiates our UHP system from 
our house nitrogen system is a set of A/B switchable Entegris 10M 
purifiers and more particle filtration.

At the moment, we have no real-time monitoring of either system ... but 
we are just about to add real-time moisture monitoring to both our house 
nitrogen and UHP nitrogen in the form of Michell Pura OL hygrometers to 
be able to measure moisture content in real time on these systems.  
While there are clearly other possible impurities in your nitrogen, I 
believe that moisture is both the most problematic and the easiest to 
measure.

As far as spot check measurements, that last time that we had our house 
nitrogen, UHP nitrogen, and argon systems measured (and we measured each 
both close to the tank and in the clean room near the end of the 
distribution lines) we observed the readings that I've reproduced in the 
following table.  Note: our last spot check occurred nearly a year ago 
(11/19/2013). We measured 3 gas systems (house nitrogen, UHP nitrogen 
and argon both near the tank and in the clean room.  We measured oxygen, 
water vapor, total hydrocarbon, and particles per cubic feet (> 0.1 um).
Note: if this table gets trashed in email translation, I'll find a way 
to post it on line.

Our most recent measurements were:

Gas 	Location 	Oxygen (ppm) 	H2O (ppm) 	THC (ppm) 	Particles
House Nitrogen 	Tank 	0.58 	0.5 	< 0.01 	56
House Nitrogen	Clean room 	0.6 	0.55 	< 0.01 	80
UHP Nitrogen 	Post Purifier 	0.028 	0.09 	< 0.01 	0
UHP Nitrogen 	Clean room 	0.038 	0.098 	< 0.01 	10
Argon 	Tank 	0.026 	0.54 	< 0.01 	14
Argon 	Clean room 	0.068 	0.55 	< 0.01 	11



While our UHP nitrogen (which comes from the same tank as our house 
nitrogen but goes through purifiers) is better than our house nitrogen, 
our house nitrogen is pretty good as well:  less than 1 ppm oxygen and 
water vapor and a reasonable number of particles ... particularly if it 
is venting a particle-laden process like sputtering or ebeam 
evaporation.  Of course, people tend to be more cavalier about using 
"PolyFlo" tubing on a house nitrogen system which can be an additional 
source of moisture at least locally. Even if that is done, if it is 
downstream of a regulator, you probably won't significantly increase 
moisture levels in other parts of your distribution system.

As a side note, we run house nitrogen from copper lines to our SRDs 
(spin-rinse dryers) because of the high flow requirements ... that may 
well cause your clean room contractor a bit of an apoplectic fit.

Of course, you would likely want to at least spot check the quality of 
your house and UHP nitrogen to see if they are comparable to ours.

Finally, most things that get vented, get opened to atmosphere at some 
point.  Air at 20% oxygen content and 45% RH can undo your very careful 
UHP venting in a matter of milliseconds ...

Good luck,

John

On 10/31/2014 9:15 AM, Milan Begliarbekov wrote:
> Hi All,
>
> At the moment we're trying to decide the purity / source of the 
> nitrogen we will use to vent our tools. The building has a bulk 
> nitrogen system that is plumbed to the clean room in copper pipes. Our 
> clean room contractor believes that that nitrogen might be too dirty 
> to use as a vent gas and recommends ultra pure nitrogen. I am 
> wondering if anyone has thoughts on this matter. I believe that it is 
> possible to get 99.998 % N2 out of copper pipes. Is that the case? If 
> not are there purifiers / dryers that are commonly used? This is only 
> a vent gas and not a process gas.
>
> Any wisdom in this matter will be highly appreciated.
>
> Best,
>
> milan
> Technical Cleanroom Manager
> CUNY Advanced Science Research Center
> Milan.Begliarbekov at asrc.cuny.edu
>
>
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