A while ago I tried doing glass fusion bonding. In my first attempt I
wanted to bond a 1mm microscope slide to another microscope slide that
had channels etched in it. I was using a simple box furnace at around
600C. In order to press the samples together I used a ceramic brick that
was laying around. I didn't want the brick to imprint itself onto the
back of my bonded slides so without thinking about it I placed a Si
wafer on top of the slides followed by the brick. After it cooled, I
found that the the microscope slides bonded to each other, as well as to
the wafer, and then the whole thing shattered when it cooled. So I'd say
that when you get up to the softening point of the glass, bonding of a
Si wafer to a microscope slide, which I don't think is precisely
polished, is quite doable. You have to be careful about matching the
thermal expansion coefficients, and also be aware that any pattern on
the glass will probably deform a little since you're actually melting
the glass.

I also have a home made anodic bonder. It's a ceramic top hotplate that
goes up to 500C along with a HV power supply connected to a metal plate
and a wire. I bond around 400C and 500-1000V depending on the type of glass.

-Joe Grogan

Gareth Jenkins wrote:
> I would think direct fusion bonding in a standard lab furnace would be
> difficult because of the differences in glass transition temperatures and
> coefficients of thermal expansion between glass and silicon.
> However, during my PhD days, I recall another student who reported making
> his own anodic bonding setup with a hotplate and a HV power supply. He
> reported success with bonding silicon to glass but unfortunately I never saw
> the setup or have any more detailed knowledge of what he did! From my
> limited knowledge of anodic bonding I believe you will need around 1kV DC,
> about 500degC and glass with sodium ions (e.g. soda-lime).