Hi K.C,

Do you mean at various points on one sample or between different samples? I've
found in the past that due to edge/loading effects the etch rates (and
particularly selectivity's) can vary across a sample. In these instances its
often apparent as a series of rings on the surface of different surface
finishes. I have managed to minimise this by using recessed platens but I'm sure
there are better ways- particularly on thinner wafers.

Daniel

-----Original Message-----
From: l j [mailto:tele992001@yahoo.com]
Sent: 08 June 2010 00:13
To: mems-talk@memsnet.org
Subject: [mems-talk] CF4 : O2 RIE of silicon, variability

Hello all,

I see great variablity in etch rate of silicon with RIE CF4:O2 etch.

At one point I see etch rate of >1um/min, at other <0.1um/min. This is at same
proces parameter setting (1:12 O2:CF4 ratio, 0.2T, 500W).

Can anyone comment on what might casue such wide variability in etch rate at
nominally constant process parameters?

Thanks in advance,
K.C.