Hi
I used 40% KOH solution at 80 deg C very freqentely during my Ph.D. work for
silicon anisotropic etching. It gives very smooth surface.
You can try this for your experiment.

Best regrads
Prem Pal
Yonsei University Seoul

>-----Original Message-----
> From: mems-talk-bounces@memsnet.org
>[mailto:mems-talk-bounces@memsnet.org]On Behalf Of GARCIA BLANCO Sonia
>Sent: 11 November 2005 15:47
>To: 'General MEMS discussion'
>Subject: [mems-talk] KOH etch fo silicon with very low surface roughness
>
>Hi,
>
>I am starting to setup a KOH silicon etch bath. I would like to get 54.7deg
>and 45deg grooves with very good surface roughness (less than 30nm would be
>ideal).
>
>Could anybody give me some suggestions about an starting point for my
>experiments and an idea of what are the most important parameters and in
>which way they will influence my etch?
>
>(I did a first trial with 35%wt KOH, 20% vol IPA, 80C, ultrasounds, very
>strong agitation and orientation of the sample vertical with the patterns
>facing the current of the flow and the surface roughness was really bad. I
>etched 80microns in 1.5h, so I think the etch rate is as reported in the
>literature. I used a PECVD silicon nitride mask).