Hello Jingru,

I think your issue might be thermal shock.  Most hot plates have a very simple
on/off controller.  This can cause the temp to jump around quite a bit.  I don't
think your top electrode plate is applying enough force to be an issue.  Give
this a try and I think you will have much better results.

1.  Place a large mass (Al or SST would be best) on the hot plate to help hold
the heat and damp the swings of the hot plate.
2.  Place the wafer stack on the on the lower chuck.
3.  Place the top electrode on the wafer stack.
4.  Heat the wafer stack to the bonding temp.
5.  Turn on the voltage and bond.
6.  At the end of the bond turn off the hot plate and let the stack cool.  The
added mass should allow the stack to cool slowly.

This should solve your cracking issue.  If you are still seeing crack along the
channels or half moon cracks then there is a good chance that you have built up
air pressure in the channels or colliding bond fronts.  If this is the case
lower the current so that the bond progresses slower and helps to vent the gas.

Good luck

Brad Johnson
Sales Application Engineer
DJK Global
US Distributor, Semiconductor Inspection Systems
2447 W. 12th St. - Suite 6, Tempe, AZ 85281
480-968-3343 Ext 112 office
602-501-4413 cell
bjohnson@djksemi.com
http://www.djksemi.com


-----Original Message-----
From: jingru zhang [mailto:ruharvard@gmail.com]
Sent: Friday, February 27, 2009 1:13 PM
To: General MEMS discussion
Subject: Re: [mems-talk] glass cracking during anodic bonding

Thank you very much for all your suggestions.

I used a homemade hotplate and power supply for the bonding process. I put
an alumina chunk on top of glass in order to apply some pressure and also to
fix the wire which is used as cathode.

 I was trying to remove the force after I shut off the electric field, But
the glass started to crack immediately after I remove the force, even before
I turned down the temperature. This may be caused by the influence of the
cooler air on top, since I don't have a chamber.