Chemistry Reference
In-Depth Information
deposition kinetics is greatly increased by illumination but decreases with increasing
HF concentration.
295,694
The deposition rate changes with time. For example, Fig. 6.12
shows that copper deposition is initially rapid but virtually ceases after
1
0min, which
is attributed to the decreased area for anodic reaction.
293
Electroless metal deposition at trace levels in the solution is an important factor
affecting silicon wafer cleaning. The deposition rate of most metals at trace levels
depends mainly on the metal concentration and some may also depend on the interac-
tion with other species as well.
483
For copper the deposition rate at trace levels in HF
solutions is different for
n
and
p
types. It depends on illumination for
p
but not
for
n
-Si.
293
It is also different in HF and BHF solutions. In a HF solution the deposi-
tion process is controlled by both the supply of minority carriers and the kinetics of
cathodic reactions.
120
-Si
only when both
and illumination are present. In the BHF solution, the corrosion process is limited
by the supply of electrons for
p
Thus, a high deposition rate occurs on
p
-Si
it is limited by the dissolution
of silicon because the reaction rate is independent of concentration and illumina-
tion. The amount of copper deposition does not correlate with the corrosion current
density, which may be attributed to the chemical reactions associated with hydrogen
reduction. More information on trace metal deposition can be found in Chapters 2
and 7.
-Si
whereas for
n
-Si
Preferential deposition of a metal onto selected areas of an electrode surface can
occur when a difference in doping type or in the amount of oxide exists on different
areas of the surface. Preferential plating of Au on the
n
region of a
p
n
junction can be
generated under illumination.
837
In this case, the
p
region acts as the anode consuming the
holes diffused from the
n
region. The greater the potential difference across the junction,
the larger is the deposition rate on the
n
region. Such selective deposition has been
used as a method for delineation of
p-n
junctions
381
and for producing micro metal
structures.
659,756
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