Hi Heiko,
we made microfluidic devices (actually devices with chambers and
channels for PCR)
consisting of Si and glass (Pyrex) using 4 inch wafers.
The Si wafer had deep-etched structures and was thermally oxidised after
etching.
The thickness of the oxide was 40 nm.
The pyrex wafer was mechanically drilled (inlet and outlet ports).

After drilling the glass wafer was cleaned using the following procedure:

2x Acetone and ultrasound 5 min. each;
1x IPA and ultrasound 5 min;
RBS 50 (15 % solution) 1 hour with ultrasound;
rinse in DI water;
Megasonic wafer cleaner with DI water;
Oxygen plasma (180 mTorr, 200W, 50 sccm in a STS 320 PC RIE) for 10 min.

The bonding process was performed in a EVG 501 wafer bonder under
atmospheric pressure.
The wafers were brought into contact (after alignment).
Contact force was 250 N.
Temperature was ramped up to 425 °C.
Hold for 30 min to achieve thermic equilibrium.
Voltage on (1000V).
Hold for 45 min.
Voltage off.
Cool down to RT with 2°C / min.

The bonding yield was 100%. The wafers could not be separated without
breaking the glass.

If you do not machine your glass wafer, you do not need such a "heavy"
cleaning procedure.
When we use new glass wafers (Borofloat 33 purchased from Planoptik
GmbH, Germany) we clean them
in RBS 50 (10...15%) for at least 1 hour (better overnight), then a
thorough rinse in DI water and
finally the megasonic cleaner (just DI water).
I found that this procedure enhances the adhesion of SU8 on glass (which
is known to be not superior).

Hopefully this will help you

best regards

Peter Svasek

Vienna University of Technology
Institute of Sensor and Actuator Systems
Vienna, Austria



H.J. van der Linden schrieb:
> Hi All,
>
> I am making a microfluidic device for electrokinetic studies. The device
> will
> consist of a channel deep-etched into silicon and a top layer consisting of
> glass. I want to use anodic bonding to bond the device.
> Because I will use the device for electrokinetic studies I need to be able
> to
> apply high voltages over the liquid in the channel. A problem here is of
> course
> that the native oxide on the silicon wafer will breakdown causing a short
> circuit
> through the silicon wafer. Therefore I want to apply an insulation layer on
> the
> silicon before the bonding. This layer will most likely be an oxide.
> The insulating layer is likely to interfere with the anodic bonding process.
> Has anyone tried a similar process ? The parameters that I am most
> interested in
> are the thickness of the insulating layer and the voltage and temperature
> for
> the anodic bonding process.... Voltages that I expect to use are around 50 -
> 250V.