Hot phosphoric acid (160 C) selectively etches nitride over oxide and
silicon.
If you need to pattern the nitride, use a polysilicon hard mask, which can
later be stripped off in a KOH dip or silicon isotropic etchant.
See papers in JMEMS for etch rates.
   --Kirt Williams

----- Original Message -----
From: 
To: "General MEMS discussion" 
Sent: Monday, October 25, 2004 5:39 PM
Subject: [mems-talk] thich Si3N4 layer


> Hi,
>
> I have a 3000A layer of Si3N4 on a 1000A layer of thermal oxide which
itself is
> on doped poly silicon, I need to etch some areas of Si3N4 and then some
ares of
> oxide under that from the opening, I wonder if anybody can suggest a
proper
> etchant for this thickness of silicon nitride?
> I wonder if anybody can help me?
>
> Thanks,
>
>
> Laleh Rabieirad
> PhD Student
> ECE Department
> Purdue University
> _______________________________________________
>