<div dir="ltr">Mark Heiden,<div><br></div><div>The UC Berkeley Marvell NanoLab has looked into house, high-purityN2 versus UHP cylinder N2 in reactive sputter applications.Using a RGA we see more contamination with using cylinder N2 than our house-delivered N2. As per your note, the NanoLab N2 is also derived from a cryogenic LN vessel. The spec from the LN vendor gives impurities of <1 ppm. </div><div><br></div><div>Having said this, N2 is delivery throughout the lab is branched to countless uses, including things like N2 blowoff guns. There is also significant use of plastic tubing and retractile hoses, all of which are subject to permeation. Partial-pressure laws invariably mean the N2 delivery system is subject to back-diffusion. Long-ago we made sure that anytime a regulator goes into the N2 circuit, especially those cheap types, it is a non self-relieving type, yet another source for back-diffusion. </div><div><br></div><div>As a sidebar to this conversation I question whether Teflon-PFA tubing and the associated fittings offer any advantage over polyethylene tubing when it comes to delivering N2 with high process purity.Teflon tubing and fittings are subject to compression-set given time and like other polymers PTFE and extrudable variants have diffusion issues.</div><div><br></div><div>Given the above we decided that in processes where N2 becomes part of a critical thin film, we will add an N2 purifier cartridge. These typically come as a compact SS cartridge with face-seal (VCR) fittings and can be exposed to air, for the short time required for installation. If you pick one of these make sure the reactive purifying material is a metal-alloy and not an organic. </div><div><br></div><div>In system, gas sticks typically have a pneumatic isolation valve (Nupro) before and after a mass flow controller (mfc). The best place to install a purifier is in this circuit. Consider adding an additional valve to isolate the purifier should an mfc needs change-out or have a VCR cap handy to protect it. </div><div><br></div><div>Given such placement the purifier cartridge will only see the actual amount of N2 requires by the process and otherwise remain isolated. Given good supply N2 purity it should last a long time - perhaps into retirements?</div><div><br></div><div>Regards,</div><div>Bob Hamilton </div><div><br></div><div> </div></div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div><div><div><div><div><br>Robert Hamilton<br></div>University of CA, Berkeley<br>Marvell NanoLab Equipment Manager<br></div>Rm 520 Sutardja Dai Hall, MC 1754<br></div>Berkeley, CA 94720<br></div>Phone 510-809-8618 (desk - preferred)<br></div>Mobile 510-325-7557 (my personal mobile)<br></div>E-mail preferred: <a href="mailto:bob@eecs.berkeley.edu" target="_blank">bob@eecs.berkeley.edu</a><br><a href="http://nanolab.berkeley.edu/" target="_blank">http://nanolab.berkeley.edu/</a></div><div dir="ltr"><br></div><div dir="ltr"><br><div><div><div><div><div><div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div>
<br><div class="gmail_quote">On Thu, Jul 30, 2015 at 3:12 PM, Mark Heiden <span dir="ltr"><<a href="mailto:mheiden@engr.ucr.edu" target="_blank">mheiden@engr.ucr.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p class="MsoNormal">We are moving a sputtering system from a remote installation into our cleanroom and the intent has been to take it “off the bottle” and use the building process nitrogen system for process gas as well as venting. The bottles on the old
install were 99.999% but the building process nitrogen is not certified to any exact number. The piping comes out of the 9000 gal. tank and through a vaporizer, then it goes through filters then splits into “house” nitrogen which is copper piping and “process”
nitrogen which is all stainless steel with 10ra polished inside. <u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">From the stainless building process nitrogen line regulator, we ran high purity Teflon PFA tubing to the point of use filter on the MFC. Since I can’t provide a precise purity for the evaporated nitrogen gas coming from the bulk tank and
the tubing from the regulator to the filters is not stainless, a PI that was using the system is terrified that the nitrogen won’t be pure enough. Could I get your opinions on what the purity may be expected to be and if it is less than 99.999% would the filters
correct this anyway? <u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">I’m sure most operations that spent the money for a “process” nitrogen system are not then running everything on bottles anyway so how do you ensure that the nitrogen being delivered to the systems is pure enough?<u></u><u></u></p>
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<p class="MsoNormal">Thanks in advance,<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Mark Heiden<u></u><u></u></p>
<p class="MsoNormal">NanoFab Cleanroom Manager<u></u><u></u></p>
<p class="MsoNormal">Center for Nanoscale Science and Engineering<u></u><u></u></p>
<p class="MsoNormal">University of California, Riverside<u></u><u></u></p>
<p class="MsoNormal"><a href="tel:951-827-2551" value="+19518272551" target="_blank">951-827-2551</a><u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
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