Silicon/Electrolyte Interface - Electrochemistry of Silicon and Its Oxide - page 67

and According to Derrien et al ., 499 a clean Si surface can be more easily oxidized
if the Si atoms displaying their covalent configuration are disrupted. This occurs
when a few metal atoms such as Au, Cu, and Pd are evaporated onto the Si surface.
These atoms interact strongly with Si and destroy the configuration, giving rise to
an intermixed surface zone where Si and metal atoms are embedded together. These
silicon atoms, liberated from their

configuration, behave as metal atoms and react

very easily with oxygen to form a film.

2.4.2. In Water and Solutions

In the presence of water for a sufficiently long time, the silicon surface is always
covered with a thin oxide film independent of the initial surface condition. The thick-
ness and the growth rate, however, depend on the initial surface condition. On a cleaved
silicon surface, representing a perfectly clean condition, an oxide of 3-4 Å is found to
grow on the surface after the cleavage in deionized water for 5-10min. 325 The stable
thickness of native oxide films on silicon surface in water, as shown in Table 2.10, is
similar to that formed in air, ranging from 5 to 10 Å. For a HF-cleaned surface, Fig.
2.20 shows that the growth of native oxide in water has two distinct stages, similar to
that in the air, with a very slow growth initially followed by a faster growth. 579 The
oxide remains relatively thin for about 3 h before increasing in thickness. The slow
growth of native oxide on the HF-treated surface is due to the hydrogen termination,
which has to be replaced by hydroxyl termination before formation of oxide. The nucle-
ation and growth of oxide tend to follow different modes in different solutions. 405,760
Also, dissolved oxygen in the water has a significant effect on the growth of the oxide
as shown in Fig. 2.20. 579 The oxide thickness increases with increasing concentration
of dissolved oxygen in the water. Since the growth rate without dissolved oxygen is
very slow, it has been suggested that the native film growth in water may require the
presence of both water and oxygen. In ozone containing water, the amount of oxide
increases with ozone concentration in the range of 0-15 mg/l. 1091 This dependence dis-
sappears at higher concentrations.