[labnetwork] KOH etch of silicon

[Matthias Pleil]

Hello Mathilde,


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).


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.


[cid:ca080029-6a86-4b61-9b30-1067e3167748]


Kind Regards,

Matthias Pleil, Ph.D.
Research Professor & Lecturer III of Mech. Eng - UNM
UNM MTTC Cleanroom Manager
PI - Southwest Center for Microsystems Education
scme-nm.org
(505)272-7157
________________________________
From: labnetwork-bounces at mtl.mit.edu <labnetwork-bounces at mtl.mit.edu> on behalf of Mathilde Isabelle Barriet <mathilde.i.barriet at ntnu.no>
Sent: Friday, August 11, 2017 7:03:06 AM
To: labnetwork at mtl.mit.edu
Subject: [labnetwork] KOH etch of silicon

Dear All,

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.

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.

If anyone has experience with this, please let me know.

Thanks
Mathilde

Senior Engineer
NTNU NanoLab
----------------------------
Sem Sælands vei 14, K1-113
NO-7491 Trondheim
+47 91 89 72 08
www.ntnu.no/nanolab<http://www.ntnu.no/nanolab>



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