Chemistry Reference
In-Depth Information
4 indicates that the dissolution process is completely electrochemical, whereas effec-
tive valence less than 4 indicates the involvement of chemical reactions. The effective
dissolution valence of silicon has been found to vary with silicon material, solution
composition, anodic polarization, and illumination conditions.
In fluoride-containing solutions the dissolution valence varies from 2 in the expo-
nential region to near 4 in the electropolishing region as shown for
-Si in Fig. 5.20.
700
p
For
-Si the dependence of dissolution valence on potential varies with illumination
intensity. At high illumination intensity, when the process is not light intensity limited,
the variation of
n
with potential is observed to be similar to that of
n
-Si. For a given
solution the dissolution valence increases with current for all types of materials as
shown in Fig. 5.21.
12
There is a sharp increase in
n
at the current density correspond-
ing to the first peak current density
p
The current range of sharp change shifts to higher
