Hello Roger,

Shay has two very good points on the sticking.  I have used several materials to
allow the Na to defuse away from the glass and prevent pitting and residue.  The
big difference I found with Borofloat is that most of the time it comes in very
dirty compared to Pyrex.  Try giving it a good RCA clean and see if that helps.
After the clean place two glass wafers together and see if they start a Van Der
Waals bond, if they start to bond locally (around your finger when you push in
them) you should be ok.  If a very large are starts to bond and the bond front
starts to self propagate then you have some very high quality glass and adding
heat and force will make a pretty good bond that will cause the sticking or even
bonding.

Graphite also works well but don't use graphite foil, it will stick and make a
huge mess.  A graphite puck will do the trick and can be used many times before
it needs to be replaced.  These can be made quite cheap.  Going to graphite also
has the advantage that you can make cutouts in the puck to fit around the clamps
on the transport fixture, this will allow you to keep a good alignment and place
the puck on top of the bond stack just before entering the bonder.  Good
alignment, good glass quality, it's a win/win.

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