LPCVD nitride doesn't etch in HF, but the deposition temperature (~835 C) is
too high.
PECVD nitrides tend to etch in HF, largely due to the lower deposition
temperature,
which allows more hydrogen to stay in the film.

I have done a series of tests to get PECVD silicon nitride with the slowest
etch rate possible.
The following helped:
    Higher temperature
    Using N2 instead of NH3 as the nitrogen source
    A higher flow of SiH4.
Doing the above might give you a film that will stand up to your HF/ethanol
solution long enough.

For other insulators, we tested evaporated Al2O3. It etched in HF.

    --Kirt Williams, Ph.D.   consulant

----- Original Message -----
From: David Wood 
To: 
Sent: Thursday, May 01, 2003 4:35 AM
Subject: [mems-talk] process resistant insulator


> Dear all,
>
> We would like some advice on the best insulator layer to withstand the
> following process steps:
>
> 1. HF/ethanol etch for a few minutes,
>
> 2. toluene at 190 C for 4 hours.
>
> As this insulator will be on already fabricated FETs any temperature steps
> cannot be too high. We have tried (unsuccessfully) photoresist (S1813 and
> AZ4562), spin on glass and polyimide. We can do PECVD oxide and nitride,
but
> these will come off instantly in the HF. Would we similarly be wasting our
> time with any sputter coated oxides deposited elsewhere - ZnO, TiO2?
>
> Any help for process suggestions with existing materials, or new options,
> would be useful.
>
> Many thanks,
>
> David Wood,
> Reader,
> School of Engineering,
> University of Durham,
> South Road,
> Durham,
> DH1 3LE.
>
> Tel: +44 191 334 2464
> Fax: +44 191 334 2407
>
> email: david.wood@durham.ac.uk
>
>
>
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