Chemistry Reference
In-Depth Information
solutions is limited due to dissolution of the oxide. Figure 5.45 shows that the thick-
ness of an anodic oxide also varies with potential in acidic fluoride solutions.
122
Since the reaction rate at potentials above is limited by the dissolution of oxide
and the dissolution rate depends on the nature of the oxides (see Chapter 4), the change
of current with potential indicates that oxide composition/structure varies with the for-
mation. The nonstoichiometric composition of an anodically formed oxide film can be
expressed as
with a higher value of
n
close to the oxide/electrolyte interface and
874
a lower value of
n
close to the Si/oxide interface.
A thicker oxide film has a bulk
composition closer to the
stoichiometric
The dissolution rate of anodic oxide
874
939
).
depends on the composition of the electrolyte as shown in Fig. 5.46.
(also Fig. 5.7
It depends little on the type of material and doping levels.
2,73,700
