Hello Chris,

The problem which you are facing is quite common. From my experience i can
tell that for isotropic etching of silicon xenon diflouride acts very
good. Its a very good etchant and you can use in the form of gas or plasma
also. The mixture which you are using is HF/Nitric acid and acetic acid
does not give a smooth surface finish. I have worked with these and i
found that these mixtures give a very rough surface finish with increase
in concentration of HF. If you have the facility to do etching with xenon
diflouride i think that would work out best. If you have any further
questions please contact me.

Have a nice day
baloo








On Wed, 11 Mar 1998, Chris Turner wrote:

>      Hello,
>
>      We are producing a micro-chemical reactor module that requires
>      isotropic etching of 100 micron wide channels in silicon.
>
>      We do this using a standard HF/Nitric/Acetic acid mixture with a
>      silicon nitride masking layer. This results in several of the channels
>      etching differently to the rest. The different channels are slightly
>      wider by about 5-10 microns and have a much rougher, almost
>      crystalline, surface finish. There are 120 channels on a wafer and
>      between 1 and 20 per cent can be different. This effect runs the whole
>      length of the channel, but neighbouring channels can be unaffected.
>
>      Has anyone seen this sort of thing before and if so is there a way of
>      preventing it?
>
>      Any help gratefully received.
>
>      Thanks
>
>      Chris Turner
>      Senior Research Engineer
>
>      =========================
>      Central Research Labs
>      Dawley Road
>      Hayes
>      Middlesex
>      United Kingdom
>
>      Tel. +44 (0)181 848 6465
>      Fax. +44 (0)181 848 6442
>      e-mail cturner@crl.co.uk
>      Web. www.crl.co.uk
>
>
>

Balaji Panchapakesan
Department of Mechanical Engineering
University of Maryland, College Park MD20740

Email:baloo@glue.umd.edu