Sammendrag
We have investigated the effects of anodic bonding on silicon dioxide
by measuring MOS capacitors situated in Pyrex cavities. We used two
different cavity depths, giving 1 µm or 200 µm vertical distance
between the gate electrode and the Pyrex. After bonding, we found that
the flat-band voltage of the capacitors situated in 1 µm deep cavities
had shifted towards more negative values. The shift corresponded to
6.6E11cm-2 - 9.0E11cm-2 increase in oxide charge density. The
capacitors situated in 200 µm deep cavities showed a slight shift in
the opposite direction, which we attribute to thermal annealing of
oxide fixed charge. The values of the flat-band voltages remained
stable after nine months of storage. In addition, we observed that the
current between the gate and the substrate contact had increased after
bonding. The increase was by a factor between 20 and 150, depending
both on cavity depth and gate geometry. The current in the capacitors
with 200 µm vertical distance to the Pyrex had returned to the initial
level after nine months of storage. The capacitors with 1 µm distance
to the Pyrex still had enhanced currents. Some explanations for our
observations are suggested.
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