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<p class="MsoNormal">If you can get access to it, I’ve had good success with vertical sidewalls on silica using a femtosecond laser.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Trumpf laser’s Top Cleave system and a sonicated KOH etch can easily do 500µm ‘drill’. The throughput is vastly faster than any traditional semiconductor approach. Note that you can’t do a partial depth so you might need to figure out a
way to bond the silica onto a substrate.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><b>From:</b> labnetwork <labnetwork-bounces@mtl.mit.edu> <b>
On Behalf Of </b>Robert Nidetz<br>
<b>Sent:</b> Wednesday, January 18, 2023 8:34 PM<br>
<b>To:</b> Howard Northfield <Howard.Northfield@uottawa.ca><br>
<b>Cc:</b> labnetwork@mtl.mit.edu<br>
<b>Subject:</b> Re: [labnetwork] Deep anisotropic etching of SiO2<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="display:none"><o:p> </o:p></span></p>
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<p class="MsoNormal">Could you mechanically remove most of the SiO2 using something like a dicing saw and then finish the removal using a wet etch? Maybe create a fin structure in the SiO2 you do not want and then let a wet etch remove the fins? Your undercut
could be reduced in this manner.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Wed, Jan 18, 2023 at 8:08 PM Howard Northfield <<a href="mailto:Howard.Northfield@uottawa.ca">Howard.Northfield@uottawa.ca</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black;background:white">That's a very deep etch.</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black;background:white">Regarding dry etching:</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black;background:white">I have recently done etch tests on PEVCD SiO2 with a SAMCO 10NR RIE:</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black;background:white">- 50W, 80sccm CF4, 16sccm O2, 3.0Pa: ~21nm/min
<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black;background:white"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black;background:white">- 25W, 25sccm SF6, 10sccm O2, 3.0Pa: ~7nm/min<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black;background:white">- 50W, 25sccm SF6, 10sccm O2, 3.0Pa: ~19nm/min<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black;background:white"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black;background:white">... yes for 500um that would be around a 417 hour etch .... not feasible/realistic.</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black;background:white">So you can probably rule out these etch recipes.</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black;background:white">Regarding wet etching, generally I find it very hard to control and mask under-cut is significant.</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black;background:white">Howard Northfield
<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black;background:white">Research Associate<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black;background:white">Advanced Research Complex (ARC)<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;color:black;background:white">University of Ottawa</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><b><span style="color:black">From:</span></b><span style="color:black"> labnetwork <<a href="mailto:labnetwork-bounces@mtl.mit.edu" target="_blank">labnetwork-bounces@mtl.mit.edu</a>> on behalf of Ningzhi Xie <<a href="mailto:nzxie@uw.edu" target="_blank">nzxie@uw.edu</a>><br>
<b>Sent:</b> Wednesday, January 18, 2023 4:23 PM<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] Deep anisotropic etching of SiO2</span> <o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal"><b><span style="font-size:9.0pt;color:#FF4233">Attention : courriel externe | external email</span></b><span style="font-size:9.0pt;color:#FF4233"><o:p></o:p></span></p>
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<p class="MsoNormal"> Dear college, <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">We want to perform a highly anisotropic, very deep (~500um) etching of SiO2 with a vertical side wall. On top of the SiO2 is nanostructures protected by photoresist. The etch depth needs to be controlled with a precision of 20% (we are
thinking of using another material as the substrate underneath the SiO2 layer, which acts as an etch-stopper). The structure and dimensions are shown in the attached image. It would be very helpful if anyone has any idea of this kind of etching (either dry
and wet chemical etch is fine).<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Thank you very much.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Best regards, <o:p></o:p></p>
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<p class="MsoNormal">Ningzhi Xie<o:p></o:p></p>
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<p class="MsoNormal">Department of Electrical and Computer Engineering<o:p></o:p></p>
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<p class="MsoNormal">University of Washington<o:p></o:p></p>
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<p class="MsoNormal">_______________________________________________<br>
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<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">-- <o:p></o:p></p>
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<p class="MsoNormal">Robert Nidetz, PhD (he/him/his)<o:p></o:p></p>
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<p class="MsoNormal">University of Michigan<o:p></o:p></p>
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