Andrea,

      Be careful about comparing TMAH and KOH re; wt% and Etch rates etc.
they are very different animals.  It is my experience that 25% wt Aqueous
KOH yields about 2-3 um/min etch rate at 90C, and of course significantly
slower at 85C since it is an Arrhenius relationship with Temp.

      In general for better surfaces go to higher KOH Concentration and
lower temperatures such as 40% wt KOH, and 60C. (25% wt is near the peak
etch rate (vs conc) for KOH)  If you use IPA make sure to use saturated
solution of IPA in the KOH etchant.  That is dissolve as much as will go
into solution at temp, and then add a 0.75 to 1 inch meniscus of alcohol on
top of the etch solution to maintain saturation throughout the process
duration.  If you attempt to use a lesser % of alcohol, it will be changing
through the life of the etch and yield unrepeatable results.  Use aat least
a lid or even better a cooled reflux lid.

Best Regards,

Wendell McCulley
www.InterMEMS.com 


-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]
On Behalf Of Brian Stahl
Sent: Saturday, February 06, 2010 3:21 PM
To: mazzolari@fe.infn.it; General MEMS discussion
Subject: Re: [mems-talk] Silicon etch low roughness



Hi Andrea,



I've achieved mirror-smooth (100) surfaces with 9:1 (25wt% TMAH

solution):IPA.  The etch rate was somewhat slower than 25wt% TMAH solution,

I think in the neighborhood of 30µm/hr at 85°C.  In general it is easy to

control the etch rates of wet etchants by controlling the temperature.  I

don't recall what the RMS roughness was.  There are numerous references in

the literature for this sort of thing.



Good luck,





Brian C. Stahl

Graduate Student Researcher

UCSB Materials Research Laboratory

brian.stahl@gmail.com / bstahl@mrl.ucsb.edu

Cell: (805) 748-5839

Office: MRL 3117A





On Sat, Feb 6, 2010 at 2:53 AM, Andrea Mazzolari
wrote:



> Hi All,

>

> i need to etch (100) silicon at low etch rate (not more than 20um/hour)

> and i need very very low roughness.

>

> I can not use HNA solutions, i can use KOH or TMAH with surfactants.

> Any suggestion about the optimal etching condition for this job ?

>

> Thanks,

> Andrea

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