> -----Original Message-----
> From: Michael D Martin [mailto:[email protected]]
> Sent: Monday, November 04, 2002 3:54 PM
> To: [email protected]
> Subject: [mems-talk] 1 micron thick low stress nitrides?
> Hi,
>   Does anyone know whether it is possible to produce low
> stress nitride
> films that are a micron thick or thicker? If so, where can I
> get them?
>   a related question ...
>   How thick of a silicon nitride film would be required to span 8mm
> after release?
>
> Thanks in advance,
>           Mike Martin

In the Microfabrication Laboratory at U.C. Berkeley,
silicon-rich, low-stress silicon nitride
is deposited using a ratio of 4 SiH2Cl2 to 1 NH3 at 835 C.
I regularly deposited a micron of this SiN without any observable problems
such as cracking or peeling.
This process should be available through the MEMS Exchange;
see http://www.mems-exchange.org/
and specifically http://www.mems-exchange.org/catalog/lsn_cvd/.

Even lower stress is obtained with a 5:1 ratio, although this is not a standard
process.
I have deposited 3 um without problem using this.
Providers might not be as eager to run high levels of SiH2Cl2 as it forms Si and
HCl
in the exhaust, which is hard on the pumps.

For prior work on large spans, look up the topic "x-ray masks."
Several groups have used gold patterns on ~1-cm spans of low-stress silicon
nitride
for x-ray masks.

        --Kirt Williams Agilent Technologies