Hello Ashwini,

I suspect that you are filling your cavities with oxygen during the electrolysis
of the glass during the anodic bonding. The silicon then pops up due to the high
internal pressure.

Regards


Tony Rogers
Applied Microengineering Ltd
Unit 8, Library Avenue
Harwell Campus
Didcot
OX11 0SG
UK
Tel.: +44 (0)1235 434341 (DL)
Tel.: +44 (0)1235 833934 (SB)
Fax: +44 (0)1235 833935
e-mail: tony@aml.co.uk
Web:http://www.aml.co.uk

-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org] On
Behalf Of ashwini jambhalikar
Sent: 23 June 2009 04:51
To: General MEMS discussion
Subject: [mems-talk] stress in Silicon[Scanned]

Dear Friends,

Can anybody suggest how to calculate stress developed in Anodically
bonded thinned Silicon wafer with slelectively unbonded region.

We are observing the following:

step 1: pockets are etched  in silicon, and bonded to glass from
etched side (anodic bonding)
pocket dimension
depth: 5 micron
length and width 500 micron

step 2: wafer is thinned from backside in DRIE.
It is observed that the pocket region(unbonded region) pops up, when
wafer is thinned to 30 micron

Is it only due to stress related to Anodic bonding, or it is also due
to the fact that silicon in thinned.

In any case is there any way to analytically find out the stress.

Ashwini.