Hi Li. Zhang

                            I etched more than 30 um down to Silicon with a
recipe that was similar what you have used. But I found no grassing. Anyhow my
hard mask was 500nm SiO2. and my recipe was as given below

SF6   468sccm
C4F8   346sccm
O2       146sccm                                     and etching for 3 seconds
and passivation for 2 seconds.

Best regards
Renil

--- On Sat, 20/2/10, Li. Zhang  wrote:

From: Li. Zhang 
Subject: Re: [mems-talk] DRIE Grass Cleaning
To: [email protected]
Date: Saturday, 20 February, 2010, 10:49 PM

Hey Renil,

The hard mask is sputtered Al with thickness of 1500A and the the depth
etched down to silicon is about 10um.

I applied an etching cycle of 3s and a passivation cycle of 1s. The flow
rate of SF6 = 200sccm and C4F8 = 100sccm.

I've heard lowing the passivation flow rate might help with grass problem,
but not quite sure.

My Best,

Li. Zhang