Hello Natsuki,

There are a couple of tricks you can try.  The easiest is to place a second
piece of float glass on top of your sample, the Na will migrate into this glass
and give you a better looking surface.  I have also used sheets of graphite foil
but it really makes a big mess to clean up and can contaminate your bonder with
particles.  You can also place a graphite puck on top of your sample, these can
be cleaned many times then thrown out when they load with NA or start to fall
apart.

Try putting on a second piece of float glass and you should be happy with the
outcome.  Most of the time you can remove the Na from the surface with Di water.

Good luck,
Brad

Brad Johnson
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


-----Original Message-----
From: Miyakawa, Natsuki [mailto:Natsuki.Miyakawa@eads.net]
Sent: Tuesday, November 03, 2009 7:18 AM
To: General MEMS discussion
Subject: [mems-talk] Anodic bonding

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