Hi Ahmed,

You can try the LSN recipe Berkeley uses which normally provide great
protection against HF etches even though the stress might range between
200-400 Mpa.  Thier recorded etch rate for LSN is ~ 1 A/min in 25:1 HF or
~55 A/min in conc. HF.  Doubling the required LSN thickness for HF etch
protection is usually good enough so you might not need such a thick layer.

DCS 100 sccm
NH3 25 sccm
Temp 835 C
Press 140 mTorr


If you desire the required stress of approx ~100 Mpa, the Stanford lab has
done some work with thier LPCVD and have gotten <100 Mpa of stress with the
recipe below.

DCS ~148 sccm
NH3 ~41 sccm
Temp   900C
Press    ~270 mTorr

However, be careful with this recipe because it has processing temperatures
above 850 C at low pressures which surpass the specs of some o-rings used in
LPCVD furnaces.

Phil Tabada


>From: "Ahmed Shuja" 
>Reply-To: General MEMS discussion 
>To: [email protected]
>Subject: [mems-talk] Recipe for Low Stress LPCVD Silicon Nitride
>Date: Fri, 03 Oct 2003 09:42:37 -0500
>
>Hello All
>
>My name is Ahmed Shuja. I am a current student at the Univeristy of
>Cincinnati. I am looking for a Recipe to try to grow 0.5-1um of Silicon
>Nitride with ~100Mpa of residual stress. The recipe handed down to me was
>for Stoichmetric Silicon Nitride. The film at 0.5um cracks and thay can be
>seen with the nacked eye. I have wafers that I grew 0.75um that are
>permenately bowed even after stripping the nitride.
>
>DCS 25sccm
>Ammonia 100sccm
>Temp:700C
>Pressure:300mTorr
>
>I am mainly concerned with the resistance of silicon nitride to dilute HF
>acid. I have found information that tends to show that low stress nitride
>is usually grown by increasing the DCS flow rate. If anyone had a good
>recipe that I can use I would really appreciate it.
>Thanks
>
>Ahmed Shuja
>Center for MicroElectronics and MEMS
>University of Cincinnati
>ECECS Dept.
>
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