When you etch multiple wafers the local temperature is higher because the
process is exothermal.

Shay

-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]
On Behalf Of Staller, Steven E
Sent: Wednesday, October 31, 2007 8:54 PM
To: mems-talk@memsnet.org
Subject: [mems-talk] TMAH Etching Silicon - loading effects

We believe we have observed a strong correlation of <100>:<1111> selectivity
to loading.

When we etch one wafer we get about ½ the selectivity as we do when we
etch 25 or more.

Is this a known phenom? Should we expect the selectivity to be effected this
dramatically?

We are talking about selectivities of >65:1 vs ~30:1.

Steve