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?

On Mon, Mar 2, 2009 at 12:57 PM, Brad Johnson  wrote:

> 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

--
Jingru