Tied in with the clean surface tip is the idea that the surfaces must be
in intimate contact in order to bond. Surface contaminants will of
course screw that up. But even with perfectly clean surfaces you need to
make sure that you are pushing your wafers together in order to make up
for stuff like bow/warp, surface roughness, etc, so that the bonding
surfaces are actually touching. Try putting some significant weight on
your sample or clamping it somehow. The fact that some spots bonded and
others didn't tells me that either you have surface contaminants
interfering, or you aren't getting good contact between the wafers.

Good luck.
Joe Grogan

Shay Kaplan wrote:
> Make sure the substrates are perfectly clean before you attach them
>
> Shay
>