[labnetwork] KOH Tank Design

Tue Jul 23 15:10:28 EDT 2013

Hi guys,
  We've been using both techniques at UofL, i.e. Teflon lined quartz tanks and 6" or 8" diameter beaker with reflux condenser.  One advantage of the quartz tanks for many our users is having the space to use a PEEK fixture for doing single sided etches.  These fixtures protect both the wafer edge and the back side during the etch resulting in a very clean looking final product.  Etches done with the fixture tend to produce a more robust wafer as one frequently has oxide defects at the edge that results in nucleation sites for cracks upon further handling.  This is also true for TMAH etches.

Michael Martin
Lab Grunt

From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Luciani, Vincent
Sent: Tuesday, July 23, 2013 9:02 AM
To: 'Tony L Olsen'; labnetwork at mtl.mit.edu
Subject: Re: [labnetwork] KOH Tank Design

Hello Tony,
This is an interesting question for me because I am considering changing strategies away from the built in tank.

First:
The approach that Jeff describes has successfully worked for me over the years in  a few different implementations including the one we have now ( by Reynolds's Tech).  I personally like the quartz or Teflon lined quartz.  I would stay away from a SS tank.

However, there is dissatisfaction in my KOH etch community that has me re-evaluating our approach.
Based on the comments and usage behavior of our users over the last few years, our KOH setup is not what they want.  Having done extensive KOH etching experiments over the years, I agree and sympathize with some of their specific complaints.

Their issues (partial list):
I want to mix a custom version of KOH etch mixture.  Don't make me use your community tank.
I don't need a large volume.  So your dedicated tank is too big.
The built -in tank is too slow, takes too long to heat and cool thus limited user throughput.
Sometimes I wonder if tank contamination from a previous users botched experiment affected mine.
I want to watch my sample etch.  There are many reasons this can be a real need.
And more!

My Issue:
They want to set up their own version for a day or two or  at a time and we don't have the space to allow folks to set up camp in a wet bench .

What I plan for next time:
One day when I replace our KOH bench I will make a bench with 3 or 4 stations, each of which have a big quartz beaker with water cooled reflux lid, thermometer (or TC) well, on a stirring hotplate with excellent lighting and good visibility of the sample during the etch.  This seems to be what most "advanced" KOH users want...at NIST anyway.  Certainly, the built-in, heated tank is perfect for some labs.  I want to poiuntb out that it is not always the case.  We definitely have  more researchers/users that would like the multiple station, raised tank version I described.

Vince

Vincent K. Luciani
NanoFab Manager
Center for Nanoscale Science and Technology<http://www.cnst.nist.gov/>
National Institute of Standards and Technology
100 Bureau Drive, MS 6201
Gaithersburg, MD 20899-6200 USA
+1-301-975-2886
[Description: CNST Horztl Color logo]

From: labnetwork-bounces at mtl.mit.edu<mailto:labnetwork-bounces at mtl.mit.edu> [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Tony L Olsen
Sent: Monday, July 22, 2013 6:03 PM
To: labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>
Subject: [labnetwork] KOH Tank Design

Dear Labnetwork

We are building a new wet bench and would like to include a dedicated KOH etch bath to replace the current methodology of glassware with stir bars on a hotplate.  We generally use a bath of 80°C.
Our wetbench vendor initially quoted a recirculated bath in a stainless steel tank.  We are concerned about the stainless, nor do we believe the Teflon or PVDF wetted surfaces in the proposed diaphragm pump will hold up to the hot KOH.  Another option we are aware of is a quartz tank heated externally by recirculated water.  I'm certain there are other options, too.
Can you share your experience with dedicated KOH baths?  What is the configuration?  What are the materials?  How do you mix/stir the bath?  What problems have you experienced?  What would you do next time?

Thank You,
tonyO

Tony Olsen
Nanofab Cleanroom Supervisor/Process Engineer
36 S Wasatch Dr, Suite 2500 SMBB
Salt Lake City,  UT  84112
801-587-0651 office
801-587-3077 fax
www.nanofab.utah.edu<http://www.nanofab.utah.edu/>

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