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<div class="moz-cite-prefix">Vito Logiudice,<br>
<br>
The UC Berkeley Marvell NanoLab supports a CVD diamond tool made
by sp3. It is CVD and not PECVD; however, I'll take a stab at a
way of ruling out your pump-stack as a source of back-diffused N2.<br>
It is unlikely N2 could back diffuse through a turbo-pumped system
from its foreline roughing pump. By chance, does this turbopump
use N2 as a bearing-purge, another source of N2? If so, is the
flow for this purge under control?<br>
<br>
One way to rule out N2 from the pump stack would be to substitute
Ar as the pump-purge gas and do a run. If your runs are long and a
cylinder of Ar does not contain enough gas (~6500 standard
liters/cylinder) to support a full run consider rental of a liquid
Ar Dewar. Depending on the size of your dry pump it likely uses
35-50 slpm of N2 purge and the turbo bearing purge would be much
less than the mech pumps N2 purge gas consumption.<br>
<br>
An RGA would be a terrific tool to review effects. Appended is a
graph from Edwards on the RGA analysis of the ratio of residual
gases from their turbos. Given the base pressure of turbos and the
throughput of your process gas the N2 partial pressure should be
nil:<br>
<br>
<ul>
<li><img src="cid:part1.08090905.05060204@eecs.berkeley.edu"
alt="Edwards STP magnetically levitated turbomolecular
pumps"></li>
</ul>
<br>
Regards,<br>
Bob Hamilton<br>
<br>
Bob Hamilton
<br>
Marvel NanoLab
<br>
University of CA at Berkeley4
<br>
Rm 520 Sutardja Dai Hall
<br>
Berkeley, CA 94720-1754
<br>
<a class="moz-txt-link-abbreviated" href="mailto:bob@eecs.berkeley.edu">bob@eecs.berkeley.edu</a>
(e-mail preferred)
<br>
510-809-8600 510-325-7557 (mobile - emergencies)
<br>
<br>
On 1/28/2013 2:23 PM, Vito Logiudice wrote:<br>
</div>
<blockquote
cite="mid:CD2C43E5.2104A%25vlogiudi@connect.uwaterloo.ca"
type="cite">
<meta http-equiv="Content-Type" content="text/html;
charset=ISO-8859-1">
<div>Dear Colleagues,</div>
<div><br>
</div>
<div>We are depositing single crystal diamond via PECVD in a newly
purchased tool dedicated to this process. Initial deposition
runs have revealed the presence of film defects caused by stray
nitrogen. The system and process gas lines have been helium
leak-tested. The load-locked process chamber is pumped down by a
turbo pump backed by a nitrogen-purged dry pump (the process
makes use of methane and hydrogen). We're wondering if the N2
purge on the roughing pump might somehow be contributing to the
problem.</div>
<div><br>
</div>
<div>I'd appreciate hearing the community's thoughts on the
possibility of nitrogen back flow from an N2-purged roughing
pump back to the process chamber.</div>
<div><br>
</div>
<div>Many thanks,</div>
<div>Vito</div>
<div>
<div>-- </div>
<div>
<p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;
font-size: 11pt; ">Vito Logiudice M.A.Sc., P.Eng.<o:p></o:p></p>
<p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;
font-size: 11pt; ">Director of Operations, Quantum NanoFab<o:p></o:p></p>
<p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;
font-size: 11pt; ">University of Waterloo<o:p></o:p></p>
<p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;
font-size: 11pt; ">200 University Avenue West<o:p></o:p></p>
<p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;
font-size: 11pt; ">Waterloo, ON Canada N2L 3G1<o:p></o:p></p>
<p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;
font-size: 11pt; ">Tel: 1-519-888-4567 ext. 38703<o:p></o:p></p>
<p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;
font-size: 11pt; ">Email: <a moz-do-not-send="true"
href="mailto:vlogiudi@uwaterloo.ca" style="color: blue; ">vlogiudi@uwaterloo.ca</a></p>
<p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;
font-size: 11pt; ">Website:
<a moz-do-not-send="true" href="https://qncfab.uwaterloo.ca">https://qncfab.uwaterloo.ca</a>/</p>
<p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;
font-size: 11pt; "><br>
</p>
</div>
</div>
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