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<p>Hello <span>Mathilde,</span></p>
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<p><span>We use KOH in a heated bath to etch crystalline silicon. Etch rates vary depending on concentration and temperature. We add a small amount of IPA for smoother etching (results in less cavitation - smaller bubbles).</span></p>
<p><span><br>
</span></p>
<p>We dilute 45% KOH by weight down to about 25% or so - it actually etches faster at the lower concentration. We start at approximately 100-105C at the start and then reduce down to 85C at the end (we etch through the wafer to a silicon nitride membrane on
the opposite, front side, of the wafer) Temperature reduction is to reduce the cavitation effects and the chance of "blowing" the membrane. KOH can be purchased at a very pure level - it is the bath you put it in which could be an issue. I've included an
image or our device, a basic pressure sensor we use to teach MEMS fabrication.</p>
<p><br>
</p>
<p><img size="2226759" id="x_img257670" tabindex="0" style="max-width:99.9%" src="cid:ca080029-6a86-4b61-9b30-1067e3167748"><br>
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Kind Regards,
<div><br>
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<div>Matthias Pleil, Ph.D.</div>
<div>Research Professor & Lecturer III of Mech. Eng - UNM</div>
<div>UNM MTTC Cleanroom Manager</div>
<div>PI - Southwest Center for Microsystems Education</div>
<div>scme-nm.org</div>
<div>(505)272-7157</div>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> labnetwork-bounces@mtl.mit.edu <labnetwork-bounces@mtl.mit.edu> on behalf of Mathilde Isabelle Barriet <mathilde.i.barriet@ntnu.no><br>
<b>Sent:</b> Friday, August 11, 2017 7:03:06 AM<br>
<b>To:</b> labnetwork@mtl.mit.edu<br>
<b>Subject:</b> [labnetwork] KOH etch of silicon</font>
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<div class="PlainText">Dear All,<br>
<br>
I have a user who wants to do KOH etch of silicon but since we do not have an established process in the lab, I am wondering if I could get some practical guidance on the best set ups.<br>
<br>
Also, this user is especially concerned about contaminating his Si wafers with metals so I wonder what degree of purity of KOH is commonly used and if buying the best quality available make a difference on the Si contamination or not.<br>
<br>
If anyone has experience with this, please let me know.<br>
<br>
Thanks<br>
Mathilde<br>
<br>
Senior Engineer<br>
NTNU NanoLab<br>
----------------------------<br>
Sem Sælands vei 14, K1-113<br>
NO-7491 Trondheim<br>
+47 91 89 72 08<br>
<a href="http://www.ntnu.no/nanolab">www.ntnu.no/nanolab</a><br>
<br>
<br>
<br>
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