<div dir="ltr"><div><div class="gmail_default" style="font-family:georgia,serif;font-size:small">Some process data regarding N2 vs He dilution:</div><div class="gmail_default" style="font-family:georgia,serif;font-size:small"><a href="https://wiki.nanofab.ucsb.edu/wiki/PECVD_Recipes#Low_Stress_Si3N4_(PECVD%231)">https://wiki.nanofab.ucsb.edu/wiki/PECVD_Recipes#Low_Stress_Si3N4_(PECVD%231)</a></div><div class="gmail_default" style="font-family:georgia,serif;font-size:small"><img src="cid:ii_m98oep9y0" alt="image.png" width="525" height="434"><br></div><div class="gmail_default" style="font-family:georgia,serif;font-size:small"><br></div><div class="gmail_default" style="font-family:georgia,serif;font-size:small">As Dr. Codreanu mentioned - you can see the Refractive Index (a proxy for stoichiometry or a high-level "quality") is the same regardless of He or N2 %, while allowing for tuning of film stress.</div><div class="gmail_default" style="font-family:georgia,serif;font-size:small">So at least from a processing standpoint, either will work.</div><div class="gmail_default" style="font-family:georgia,serif;font-size:small"><br></div><div class="gmail_default" style="font-family:georgia,serif;font-size:small">(FYI, I made this plot pretty early in grad school, so plotting N2 vs He, where the He came from the 98% He dilution of SiH4, and N2 was the actual MFC gas flow I varied, may or may not be the "correct" plot to have generated...)</div><br clear="all"></div><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><font face="georgia, serif" size="4">-- Demis </font><font face="georgia, serif" size="1">(<a href="https://wiki.nanotech.ucsb.edu/wiki/Demis_D._John" target="_blank">contact info</a>)</font><div><i style="font-family:"times new roman",serif">Reminder</i><span style="font-family:"times new roman",serif">: The NanoFab has a </span><a href="https://wiki.nanotech.ucsb.edu/wiki/Frequently_Asked_Questions#Publications_acknowledging_the_Nanofab" style="font-family:"times new roman",serif" target="_blank">publications policy</a><font face="georgia, serif" size="4"><br></font></div></div></div></div><br></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Mon, Apr 7, 2025 at 4:48 PM Paolini, Steven <<a href="mailto:spaolini@cns.fas.harvard.edu">spaolini@cns.fas.harvard.edu</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="msg-5188294767097912549">
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SiH4 diluted in Helium poses pumping challenges. Helium is notoriously hard to pump with a turbo and the large amount of mixture needed to grow Si films leads to problems with pressure control and deposition rates. I know I will attract some arguments against
using 100% SiH4 but the main reason to use a pure mixture is to reduce the amount of cylinder changes that are well documented as being the main source of accidents.</div>
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Equipment Dood.</div>
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Steve Paolini</div>
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<div id="m_-5188294767097912549divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> labnetwork <<a href="mailto:labnetwork-bounces@mtl.mit.edu" target="_blank">labnetwork-bounces@mtl.mit.edu</a>> on behalf of Nathan Aultman <<a href="mailto:naultman@creol.ucf.edu" target="_blank">naultman@creol.ucf.edu</a>><br>
<b>Sent:</b> Monday, April 7, 2025 10:49 AM<br>
<b>To:</b> <a href="mailto:labnetwork@mtl.mit.edu" target="_blank">labnetwork@mtl.mit.edu</a> <<a href="mailto:labnetwork@mtl.mit.edu" target="_blank">labnetwork@mtl.mit.edu</a>><br>
<b>Subject:</b> [labnetwork] PECVD dilute gas question(s)</font>
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<p><span style="font-size:11pt">Hello Labnetwork,</span></p>
<p><span style="font-size:11pt"> </span></p>
<p><span style="font-size:11pt">We have a PECVD system using dilute silane (2%)/N2. Some labs with similar systems use dilute silane (5%)/helium. We are nearing the end of our current cylinder and will need a replacement soon. What
are the advantages and disadvantages when choosing the dilute gas? Does choosing a helium mixture produce more desirable films and/or quality? In other words, is it worth it to purchase a cylinder with helium? Also, what would be the reason(s) for using
helium as an additional process gas? E.g., a separate MFC and gas line.</span></p>
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<p><span style="font-size:11pt">Thank you all in advance.</span></p>
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<p><span style="font-size:11pt;font-family:"Times New Roman",serif">Nathan C. Aultman</span></p>
<p><span style="font-size:11pt;font-family:"Times New Roman",serif">University of Central Florida</span></p>
<p><span style="font-size:11pt;font-family:"Times New Roman",serif">407-823-6852</span></p>
<p><span style="font-size:11pt;font-family:"Times New Roman",serif"><a href="mailto:naultman@creol.ucf.edu" target="_blank"><span style="color:rgb(5,99,193)">naultman@creol.ucf.edu</span></a></span></p>
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