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<p class="MsoNormal"><span style="color:#1F497D">Hi Joe,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Masking to protect the Al contact pads from HF is tricky.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Not sure if you can change the structure but, if the sacrificial layer to free the devices would be silicon, you may consider the improved TMAH solution proposed in this paper:
<a href="https://www.sciencedirect.com/science/article/pii/S092442470000546X?via%3Dihub">
https://www.sciencedirect.com/science/article/pii/S092442470000546X?via%3Dihub</a>
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">I used it to make sensors on suspended membranes with Al pads exposed some 20 years ago…
</span><span style="font-family:Wingdings;color:#1F497D">J</span><span style="color:#1F497D"> and it works nicely. It’s a bit time consuming to prepare… (<a href="https://www.researchgate.net/publication/237115771_Low-power_micro-scale_CMOS-compatible_silicon_sensor_on_a_suspended_membrane">https://www.researchgate.net/publication/237115771_Low-power_micro-scale_CMOS-compatible_silicon_sensor_on_a_suspended_membrane</a>)
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">I hope it helps.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal" style="background:white"><span style="font-size:10.0pt;font-family:"Rotis SansSerif Std",sans-serif;color:black">Kind regards,<o:p></o:p></span></p>
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</span><span style="font-size:12.0pt;font-family:"Rotis SansSerif Std",sans-serif;color:black"><o:p></o:p></span></p>
<p class="MsoNormal" style="background:white"><span lang="EN-GB" style="font-size:10.0pt;font-family:"Rotis SansSerif Std",sans-serif;color:black">Gheorghe IORDACHE, PhD Physics</span><span style="font-size:10.0pt;font-family:"Rotis SansSerif Std",sans-serif;color:#1F497D">,
MBA<o:p></o:p></span></p>
<p class="MsoNormal" style="background:white"><span style="font-size:10.0pt;font-family:"Rotis SansSerif Std",sans-serif;color:#1F497D">Director, Nanofabrication Core Lab
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<p class="MsoNormal"><b>From:</b> labnetwork [mailto:labnetwork-bounces@mtl.mit.edu]
<b>On Behalf Of </b>Maduzia, Joseph Walter<br>
<b>Sent:</b> 26 October 2021 23:49<br>
<b>To:</b> labnetwork@mtl.mit.edu<br>
<b>Subject:</b> [labnetwork] Mask of Al in HF<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hello,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Does anyone have any suggestions for mask materials to protect Al in HF 49% for SiO2 removal in SOI wafer? The device is SOI, ICP DRIE etched to glass, HF etch to undercut and free devices, but have Al contact pads and AL is dep’d first.
Typically we use PR as pattern mask, but the Al is etching behind the PR. In this case the Al is deposited first, so although order of operations change might help, it’s not a good option atm.<o:p></o:p></p>
<p class="MsoNormal"><br>
Thank you for any suggestions you might have!<o:p></o:p></p>
<p class="MsoNormal"><b><span style="color:#13294B;text-transform:uppercase">JOE MADUZIA</span></b><span style="color:black"><br>
</span><i><span style="color:#13294B">MNMS Laboratory Specialist</span></i><span style="color:black"><br>
<br>
</span><span style="color:#13294B">The Grainger College of Engineering</span><span style="color:black"><br>
</span><span style="color:#13294B">Mechanical Science and Engineering</span><span style="color:black"><br>
<br>
</span><span style="color:#13294B">2239 Sidney Lu Mechanical Engineering Bldg</span><span style="color:black"><br>
</span><span style="color:#13294B">1206 W. Green</span><span style="color:black"><br>
</span><span style="color:#13294B">Urbana, IL 61801</span><span style="color:black"><br>
</span><span style="color:#13294B">217.244.6302 | </span><a href="mailto:jmaduzi2@illinois.edu">jmaduzi2@illinois.edu</a><o:p></o:p></p>
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