Silicon/Electrolyte Interface - Electrochemistry of Silicon and Its Oxide - page 66

with the same doping level the growth rate is faster on n- Si than p- Si . The growth rate
is greater on <111>-oriented than <100>-oriented surfaces, which is similar to thermal
325,510
Composition of the air also has a strong effect on the initial growth of the native
oxide. Water content in the air strongly affects the growth of native oxide as can be
seen in Table 2.11. 579 The growth kinetics are determined by the nature of adsorption
of oxygen and water molecules onto the surface. 180,701,887 Oxide does not grow much in
air containing very little water. 99,579
Factors such as solution composition, dipping time, and water rinse are impor-
tant in the formation of native oxide as they affect the surface condition in terms of the
type and relative amount of adsorbed species as well as surface roughness. 99,555,560,579
For example, the pH of buffered HF solutions is found to be an important factor in
determining the formation of native oxide in air as shown in Fig. 2.18. 634 The growth
rate is much slower in solutions having lower pH values due to the larger amount of
Si-F bonds on the surface.
In particular, metallic impurities on the silicon surface, arising from contamina-
tion in the cleaning solutions, strongly enhance oxide growth. Figure 2.19 shows that
the oxide growth rate in the air increases with copper content on the surface. 560 A copper
coverage of 5% of a monolayer leads to a full layer of oxide within 2 min. The copper
is found to be located at the interface. Also, during the oxide growth, part of
the copper shows a change in the oxidation state, forming a mixture of elemental copper

oxides.