Operating instructions
Process Description
Copyright © 2013 EVG 13
2
2
2.2 Anodic Wafer Bonding
Initially reported for joining a metal surface to a glass surface, the term
“anodic bonding” is used today mainly to identify the bonding of silicon
wafers to glass wafers with high content of alkali oxides (fig. 2). The
glass materials mostly used for anodic bonding are Borofloat from
Schott Glass - Germany, and Pyrex7740 from Corning Inc., USA.
The bond occurs when the two wafers are heated after being brought in
contact and an electric field is applied. At a certain temperature
(depending on the glass composition) oxides dissociate and the mobile
alkali ions are driven by the electric field into the glass, creating an
oxygen rich layer at the silicon-glass interface. Oxygen ions are driven
by the electric field to the silicon surface and produce oxidation of Si.
The resulting bond strength is very high and the process is irreversible.
In terms of equipment, it is important for the bond chamber to provide
good temperature uniformity and ensure good electrical contacts.
Figure 9a - Anodic wafer bonding process flow
Figure 2b - Bonding mechanism
145 of 370