Chemistry Reference
In-Depth Information
evolution may significantly compete with copper deposition particularly at very low
copper concentrations.
293
The characteristics of the
i
V
curve for gold deposition onto
n
-Si in a solution are similar to those for copper.
848,1145
Deposition of metals on a silicon surface can be either a conduction band process
or a valence band process depending on the redox potential of the metal and solution
composition. Deposition of Au on
p
-Si in alkaline solution occurs only under illumi-
nation indicating that it is a conduction band process due to the unfavorable position
of the redox couple for hole injection.
848
On the other hand, deposition of platinum on
p-
Si can occur in the dark by hole injection into the valence band. For Cu, although
the deposition proceeds via the conduction band as shown in Fig. 6.9, it can also proceed
via the valence band because a large anodic current of
n-
-
occurs in the dark in copper-
containing HF solution as shown in Fig. 6.10.
256
The reduction of copper under this
condition is via hole injection. The holes are consumed by silicon dissolution and the
silicon reaction intermediates then inject electrons into the conduction band, resulting
in the anodic current on
Si
-Si in the dark.
The electroless deposition of metals on a silicon surface in solutions is a corro-
sion process with a simultaneous metal deposition and oxidation/dissolution of silicon.
The rate of deposition is determined by the reduction kinetics of the metals and by the
anodic dissolution kinetics of silicon. The deposition process is complicated not only
by the coupled anodic and cathodic reactions but also by the fact that as deposition
proceeds, the effective surface areas for the anodic and cathodic reactions change. This
is due to the gradual coverage of the metal deposits on the surface and may also be due
to the formation of a silicon oxide film which passivates the surface. In addition, the
metal deposits can act as either a catalyst or an inhibitor for hydrogen evolution. Fur-
thermore, the dissolution of silicon may significantly change the surface morphology.
n
