hydrophilization by boiling in nitric acid at 70 degree cent. can improve the
bonding. u also need to c the surface roughness. It should not be more than 50
angstrom. hope it might help.

Annalisa Cerutti  wrote:Hi,
I want to bond two silicon wafers with thermal oxide (0.5 um) on the
surface.
I tried to bond them in vacuum, with a bonding pressure of 4000 mbar and at
a temperature of 500 °C. Then I performed an annealing at 900 °C for 15
hours. The result was that only small areas bonded.
To improve this result I cannot rise the temperature.
What can I change to improve bonding?
Is O2 plasma activation interesting to hydrophiize the surface?
Do I need a preparation of the surface to hydrophilize it?

Thank's

Annalisa Cerutti