That kind of anodic bond is definitely possible - the general elements for the
physics still exist.  The requirement is that a certain amount of current be
achieved to cause sodium migration away from the bond interface. The biggest
limitation will be the resistance of the oxide.  Luckily, the resistance of the
oxide is a function of temperature.

At room temp, SiO2 has a resistivity of ~1E13 ohm-m.  But at 600C, that drops to
~70,000 (and all the way to .004 at 1300ºC).  Using a power based function (only
an approximation, but the closer to known values, the more accurate it is), we
can estimate 200,000 ohm-m at 500ºC, or 650,000 ohm-m at 400ºC.

Now, one thing to keep in mind - resistance is resistivity /area.  However, as
we are primarily concerned with current flux (since current will increase with
the area of the wafer), resistivity is the best term to use.

At 200,000 ohm-m, .5 µm of oxide will provide 1000 ohm-m2 of resistivity.  Using
a 2000V potential, assuming the oxide resistance is dominating initially, this
would still allow a current density in the initial stages of the bond of2A/m2,
which is sufficient for anodic bonding (this translates to 63mA for a 200mm
wafer - definitely well within bondable range).

If we lower the bonding temperature to 400ºC, then the current flux drops to
.61A/m2 - the bond may work at this point, but I wouldn't be sure.

Best Regards,
Chad Brubaker

EV Group
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Senior Process Technology Engineer - Direct: +1 (480) 305 2414, Main: +1 (480)
305 2400 Fax: +1 (480) 305 2401
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E-Mail: [email protected], Web: www.EVGroup.com

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Kuijpers, P e m
Sent: Friday, September 19, 2008 4:35 AM
To: [email protected]
Subject: [mems-talk] Anodic bonding

Hi,

Can we perform anodic bonding on Pyrex and SOI wafers?
Thickness of the oxide layer is app.0.5 µm.
Maybe some recipe guidelines also.

Thanks.

Peter Kuijpers
mailto:[email protected]