Hi Craig,

I once tried to do something similar, but with a 10um membrane.  I never
actaully tested the repeatablility of the etch rate, but instead tried
to measure the depth of the feature (using a microscope) as it was
etched (the measurement error using the microscope was about 5um!).  But
even if you can get a repeatable etch rate, the real problem will be
uniformity across the surface of the wafer.  While a feature at the
centre of the wafer may have a 3um membrane, the features at the edge
are likely to be etched through.  In the end, I used SOI wafers with the
oxide layer as an etch stop.

Good luck,
Keith

Craig Lowrie wrote:

>Hello all,
>
>I am hoping that people out there with experience with the DRIE process
>could please tell me with what accuracy is it possible to get the DRIE
>to stop in a silicon wafer? I am wanting to be able to etch up to 300 um
>deep and be able to define a membrane thickness of 3 um with quite a
>high degree of accuracy.  Is this done by considering the etch rate?
>
>Regards,
>Cragi
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