Thanks for your answer!!

In which position do you place the sample in the bath to minimize the effect
of the bubbles? At the moment I am placing it vertical and I am also using a
stirrer in the bath. Basically, the patterns are directly in the flow of the
KHO solution.....

Best regards,

Sonia.


-----Message d'origine-----
De : de la Fuente, Pablo [mailto:pdlfuente@ceit.es]
Envoyé : Friday, November 11, 2005 11:22 AM
À : General MEMS discussion
Objet : RE: [mems-talk] KOH etch fo silicon with very low surface
roughness


Hi Sonia,

I don't know if the ultrasounds are enough, but I would try stirring the
bath (with a magnetic stirrer, for example) in order to help the H2 bubbles
formed in the etched surface to go away.

I would also recommend an immediate washing with DI water of the wafer after
pulling it out from the bath to avoid "clouds" formed in the surface. I
think it could also help using a lower concentration (20% wt KOH) etchant.

I don't know if IPA helps, I have never used it for KOH dilution. I use SiO2
for the mask.

H2 bubles travel upwards to the surface of the bath, and if you have to etch
big surfaces maybe you have "shadows" over the structures, in the direction
of the flow of the H2 bubbles, especially if you have high rate of aspect
structures.