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Steve:<br>
<br>
Thanks for your comments about use of sub-atmospheric regulators to
avoid the problems associated with heat tape on low vapor-pressure
gases.<br>
<br>
As I've never used these regulators, I've got a few followup
questions. In particular, my guess is that you are balancing the
pressure set point so that you have a low enough line pressure that
you don't have liquification problems but high enough pressure that
you maintain enough differential pressure across your MFCs. Correct?<br>
<br>
In LPCVD systems, what is your recommended pressure set point for
DCS and BCl3? Do you have an anhydrous HF vapor etch tool and, if
so, do you also use a sub-atmospheric regulator on it?<br>
<br>
Do you find that some MFCs are better than others when they have
less than 15 PSI differential pressure across them?<br>
<br>
If you have a considerable line length between your gas cylinder and
the tool, would you place your sub-atmospheric regulator closer to
the tool or closer to the cylinder? Does that choice depend on the
magnitude of temperature variation at the cylinder and/or along the
line, assuming that temperature stability is pretty good at the tool
... but maybe not so good along the line or at the cylinder?<br>
<br>
If you had a VMB between your cylinder and multiple tools, would you
use a single sub-atmospheric regulator upstream of the VMB or
individual regulators on each tool?<br>
<br>
Do you expect that this approach would work equally well for a
higher pressure process like epi where deposition pressures might be
as high as 100 Torr (~2 PSIA)?<br>
<br>
I, for one, wish I didn't have so much experience with heat tape ...
and thank you for your insights on an alternative approach.<br>
<br>
Thanks again,<br>
<br>
John<br>
<br>
<div class="moz-cite-prefix">On 1/21/2015 1:13 PM, Paolini, Steven
wrote:<br>
</div>
<blockquote
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<div class="WordSection1">
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Hmmm,<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">
Not knowing the watt/foot rating of the trace, my first
guess would be that it got too hot under all that
insulation. I have never heard of straight vs. spiral
advantages or disadvantages but I would be willing to bet
that at the fastener locations, the trace would have
<i>cool </i>spots since the heat is being transferred to
the tubing more efficiently.
<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I
quit using heat trace for low vapor pressure materials into
vacuum systems years ago, I’m assuming your DCS is being
used for LPCVD and that would be a perfect candidate for
running the gas at sub-atmospheric pressures to lower the
boiling point. I use this method with all my
prone-to-liquify-high-vapor pressure gases and have never
experienced a “flooded” MFC since doing so.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Best
of luck<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Steve
Paolini<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Equipment
Dood<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Harvard
University Center for Nanoscale Systems<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><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>Vito Logiudice<br>
<b>Sent:</b> Wednesday, January 21, 2015 12:23 PM<br>
<b>To:</b> Labnetwork<br>
<b>Subject:</b> [labnetwork] Heat trace issues on DCS
gas lines<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<p class="MsoNormal"><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black">Dear
Colleagues,<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black">We
are experiencing an issue with the heat trace on our
Dichlorosilane gas line. The all-welded 1/4" SS line is
encapsulated with a 1/2" SS outer containment line which
is itself heat traced with a single strand of heat trace
that runs the entire length of the coax assembly. The 120
foot line is insulated as shown in the attached photo. A
portion of the heat-trace appears to have failed
prematurely (it was installed less than one year ago) and
we are wondering if the method of installation may be the
cause.<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black">The
heat trace was not installed in a spiral fashion around
the outer 1/2" tube. Rather it was installed in a straight
fashion along its entire length with "heat trace fastening
tape" located every four feet or so. A member of my team
has suggested that such a straight rather than spiral
installation may have caused hot spots (at the fastening
locations) which may have in turn caused the failure.<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black">I
would appreciate hearing from the community on this point:
Are the heat traces around your low pressure gas lines
spiral-wound around the lines or are they installed in a
straight fashion and somehow fastened along the entire
length?<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black">Other
insights/suggestions on the proper heat tracing of gas
lines by experts in the field as well as comments on
possible causes of premature heat trace failure are very
much welcome and appreciated. Thank you.<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black">Regards,<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black">Vito<o:p></o:p></span></p>
</div>
<div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">--</span><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Vito
Logiudice P.Eng.</span><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Director
of Operations, Quantum NanoFab</span><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">University
of Waterloo</span><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Lazaridis
QNC 1207</span><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">200
University Avenue West</span><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Waterloo,
ON Canada N2L 3G1</span><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Tel.:
(519) 888-4567 ext. 38703</span><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Email: <a
moz-do-not-send="true"
href="mailto:vito.logiudice@uwaterloo.ca">vito.logiudice@uwaterloo.ca</a></span><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.5pt;font-family:"Calibri","sans-serif";color:black">Website: </span><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><a
moz-do-not-send="true"
href="https://fab.qnc.uwaterloo.ca">https://fab.qnc.uwaterloo.ca</a><o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:11.5pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
</div>
</div>
</div>
<br>
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