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Rick: <br>
<br>
This is an excellent question and I thank Tom Tribble and John
Nibarger for their initial contributions to this topic ... and
others that will undoubtedly soon follow.<br>
<br>
First, let me get my remedial class question out of the way: Tom,
you've got me feeling like a rank beginner. I must confess to being
unfamiliar with the 1<span style="color:#1F497D">δ, 3</span><span
style="color:#1F497D">δ, and 6</span><span style="color:#1F497D">δ
notation for gas purity. Is this the equivalent of what I know as
dot notation? In other words, so they correspond to 1-, 3-, and
6-nines purity that is 1.0, 3.0, and 6.0 in dot notation? Where
99.5% purity is 2.5?</span> Or is <span style="color:#1F497D">δ
notation something different?</span><br>
<br>
I would like to add confirmation of your "unofficial audit" that
found that 10% of your usage demands high purity.<br>
We also have a 9000 gallon LN2 tank (which, sadly, gets filled every
fourth day). We have two sets of vaporizers on it: the big set
supplies the copper-piped "house N2" and the smaller vaporizers that
also go through a switchable set of purifiers and then feed our
stainless-piped "UHP N2" system. Nouse N2 usage is dominated by
pump purge. We have totalizing flow meters on each main line and
typically observe that the UHP N2 consumption is 130-200 SLM and the
house N2 consumption is 2500-2800 SLM. In other words our total
nitrogen flow is very close to 3000 SLM (or about 4.5M - 5.0M SCF
per month!). In other words, our high-purity consumption is in the
range of 5-7% of our total consumption. Note: we actually use the
house nitrogen for our SRDs ... if we moved that intermittent
high-flow to UHP N2, it probably gets us close to, but no higher
than, 10%.<br>
<br>
My question to the labnetwork community is what level of nitrogen
purity would you want for pump purges of some of our nastier
processes? For example, things like DCS and ammonia for LPCVD
nitride? Hydrogen, germane, silane, plus dopants for an epitaxial
process? is 1.0 nitrogen good enough? The way that I look at it,
that is only a 50% reduction of oxygen as compared to what you find
in air. How about 2.0 nitrogen (99%), good enough?<br>
<br>
And one question to John Nibarger: is the moisture content of your
generated nitrogen controlled by the moisture content of your feed
CDA? In other words, with your incoming CDA dew point of -40C is
the dew point of your generated nitrogen also approximately -40C?
If the incoming CDA were drier (say -55C to -60C) do you expect that
your generated nitrogen would also be that much drier? I ask
because for pumps running corrosives such as HCl, Cl2, BCl3, and HBr
it would seem that dryness of the purge gas would be more important
than the background oxygen content.<br>
<br>
Thank you all,<br>
<br>
John<br>
<br>
<br>
<div class="moz-cite-prefix">On 3/24/2015 1:31 PM, Tribble, Thomas
wrote:<br>
</div>
<blockquote
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<p class="MsoNormal"><span style="color:#1F497D">Richard,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">We haven’t
switched to onsite generation for the fab, but we (Harvard)
have looked at it. The Harvard fab has a 9000 gallon LN2-
3δ storage that gets re-filled approximately once a week.
The storage facility occupies approximately 300 GSF, and
there is no more real estate available for this purpose.
Based upon a much smaller on-site generator recently
completed, on-site generation to replace the fab storage
facility would require more real estate than is available.
Part of the demand for space is the self-imposed requirement
for N+1 redundancy. This also affects the capital budget.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">But if saving
money is your focus, I suggest that your discussion should
be focused on the purity of your gas requirements. Locally
generated 1δ gas is
<s>inexpensive</s> cheap to produce. Locally generated 3δ
gas is moderately expensive to produce. Locally generated
6δ gas is
<b>very</b> expensive to produce. From the refinery, 3δ gas
is all that is produced and transported. What we at Harvard
use is 6δ gas (3δ gas run through a purifier). An
unofficial audit has shown that less than 10% of our usage
actually demands 6δ purity.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Want to save
money? Figure out your demand by purity and segregate the
flows (piping). Provide your pump and gas cabinet purges
with on-site generated 1δ gas. Your facility will save.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Tom Tribble<o:p></o:p></span></p>
<div>
<div style="border:none;border-top:solid #B5C4DF
1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">
<a class="moz-txt-link-abbreviated" href="mailto:labnetwork-bounces@mtl.mit.edu">labnetwork-bounces@mtl.mit.edu</a>
[<a class="moz-txt-link-freetext" href="mailto:labnetwork-bounces@mtl.mit.edu">mailto:labnetwork-bounces@mtl.mit.edu</a>]
<b>On Behalf Of </b>Morrison, Richard H., Jr.<br>
<b>Sent:</b> Tuesday, March 24, 2015 12:04 PM<br>
<b>To:</b> <a class="moz-txt-link-abbreviated" href="mailto:labnetwork@mtl.mit.edu">labnetwork@mtl.mit.edu</a><br>
<b>Subject:</b> [labnetwork] LN2 vs N2 generation on
site<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hi everyone,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I am paying >$220K per year for LN2 to
generate Nitrogen for my fab. Have any of you guys switched to
onsite Nitrogen generator?
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Looking for ideas on:<o:p></o:p></p>
<p class="MsoNormal" style="text-indent:.5in">Cost of system<o:p></o:p></p>
<p class="MsoNormal" style="text-indent:.5in">Maintenance cost
of system <o:p></o:p></p>
<p class="MsoNormal" style="text-indent:.5in"> Quality of the
Nitrogen.<o:p></o:p></p>
<p class="MsoNormal" style="text-indent:.5in">Operating cost per
CuFt of Nitrogen<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Rick<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Draper Laboratory<o:p></o:p></p>
<p class="MsoNormal">Principal Member of the Technical Staff<o:p></o:p></p>
<p class="MsoNormal">Group Leader Microfabrication Operations<o:p></o:p></p>
<p class="MsoNormal">555 Technology Square<o:p></o:p></p>
<p class="MsoNormal">Cambridge Ma, 02139-3563<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><a moz-do-not-send="true"
href="http://www.draper.com">www.draper.com</a><o:p></o:p></p>
<p class="MsoNormal"><a moz-do-not-send="true"
href="mailto:rmorrison@draper.com">rmorrison@draper.com</a><o:p></o:p></p>
<p class="MsoNormal">W 617-258-3420<o:p></o:p></p>
<p class="MsoNormal">C 508-930-3461<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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