Hi Prem,

Yes, I have tried this with cantilever strips and it has worked very
well indeed for through-thickness etch depths in the Si substrate. The
trouble is that the SU-8 will detach from the Si/SiO2 surface
following immersion in the KOH etchant - a couple of minutes at most
when the solution is heated - without some form of physical restraint.
To secure the SU-8 strips to the substrate, etching through an oxide
mask, I used mechanical interlocking to fix the cantilever roots. The
process involved etching small pits into the Si wafer, re-oxidisation,
then spinning/patterning the SU-8. The polymer will fill the pits
during regular spinning, and provide firm physical attachment once
cured, to allow hybrid Si-polymer structures to be released by either
wet or dry etching.

Details of the full process are provided in the following paper:
Journal of Micromechanics and Microengineering, Volume 15, Issue 11,
pp. 2074-2082 (2005).

You could also have a look at the following ref for an RF application
benefiting from the process: J. Micromech. Microeng. 16 2021-2033,
2006

Lastly, I also devised a basic work-around, based on a similar
concept, to secure SU-8 on glass substrates for in-service robustness
- aimed more at microfluidic, optical and RF MEMS applications: J.
Micromech. Microeng. 16 S161-S168, 2006

I can send you some SEM more shots if you are interested.

Regards,

Michael


> ---------- Forwarded message ----------
> From: "Prem Pal" 
> To: "General MEMS discussion" 
> Date: 6 May 2008 09:25:18 -0000
> Subject: [mems-talk] SU-8 structure using wet etching
> Dear all
>
> Anybody have an experience of releasing SU-8 microstructures (i.e. cantilever
beams) on silicon wafer using wet anisotropic etching, like SiO2/Si3N4 or P++ Si
structures.
> All kinds of suggestions would be highly apreciated.
>
> Best regards
> Prem Pal
> Nagoya University Nagoya, Japan