Dear all,

When I bond glass wafer (Borofloat33, Schott) with silicon wafer
anodically, then I observe lot of small spots on the back side of the
glass wafer which make the glass to appear rather cloudy. So far as I
understand  this phenomenon is due to locally concentrated sodium ions.

My question: Is there any method to avoid this happens so that the glass
wafer remains clear and transparent after the anodic bonding?

Thanks!

Regards

Natsuki