You might want to try something that holds heat much better than alumina such as
SST or SiC.  If you can't find SST or SiC, then keep the top chuck on the bond
stack and slowly lower the temp so that the entire stack cools together.  Once
the wafers hit 50C they should be good to handle without cracking due to CTE
issues.

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:jingru@eden.rutgers.edu]
Sent: Tuesday, March 03, 2009 9:19 AM
To: General MEMS discussion
Subject: Re: [mems-talk] glass cracking during anodic bonding

Hi Brad,

Thank you very much for your advice. I used alumina chucks on both bottom
and top of the sample to fix the electrode and also slow down the cooling
rate. Do you think Al or SST will work better than alumina?