Chemistry Reference
In-Depth Information
for applications in the etching of silicon. For the organic redox couples, the potentials
are commonly determined by measuring the average of the cathodic and anodic current
peaks of the reaction on a Pt electrode against a reference electrode.
552
This practice
assumes that the electrode reactions for the redox couples at the Pt electrode are
reversible.
6.5.1. Individual Redox Couples
is an agent widely used for crystal defect etching. The kinetics of
its reduction reaction in relation to etching silicon in HF solution has been systemati-
cally investigated by Meerakker and Vegchel.
195,196
Figure 6.16 shows the
i-V
curves
measured in a high
ratio solution for
n
-Si and
p-
Si.
A cathodic plateau current
-Si indicates the injection of holes into the valence band by the reduction of
This current is proportional to the concentration of and is essentially independent
of HF concentration. Rotation of the electrode has a very slight effect on the reaction
rate indicating that the reaction is almost fully kinetically controlled. There is a shoul-
der on the cathodic
i-V
curve on
n
-Si, the magnitude of which is similar to that of the
current plateau on the
p-
on
p
due to the reduction of The reaction in the current
plateau region is hydrogen evolution and the plateau current on
p-
Si
Si
increases with illu-
mination with a quantum efficiency of 1.
At low ratios a reduction peak followed by a lower current plateau at
more negative potentials occurs on
n-
as shown in Fig. 6.17
196
indicating
the inhibition of the reaction as a result of the reduction reaction. Both the peak and
plateau currents are independent of the
Si
and
p-
Si
concentration but dependent on the HF
