Chemistry Reference
In-Depth Information
and This effect is attributed mainly to the implanted ions and not to radiation
damage. On the other hand, implantation of and a decrease
in the oxidation rate, which is attributed to radiation damage. As an example, Fig. 3.10
shows that the cell voltage for high doping material at the beginning of the anodiza-
tion is much lower at a given current density indicating a much lower current efficiency
during the anodization with increasing dose. The increased current density with the
implant concentration is due to the increase of generation-recombination centers, espe-
cially at concentrations higher than
605,790
Surface roughness may affect the
oxidation kinetics, especially the initial stage.
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It has been reported that growth rate
and uniformity of anodic oxides can be better controlled by using two anodes, a disk
anode in the middle and a ring anode at the perimeter.
457
ions causes
3.3.4. Effect of Polarization Conditions
Anodization can be carried out under different modes with constant potential
(potentiostatic mode) or constant current (galvanostatic mode). Constant potential
means that the oxide grows under different field strengths from the start to the end of
anodization, whereas constant current means that the oxide grows under a constant field.
Most studies on the anodization of silicon employ the galvanostatic mode.
It has been found that the mode of polarization particularly at the initial stage has
a great effect on the further growth of the oxide.
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If the oxide is grown at a higher
potential, then the final oxide will be significantly thicker. Figure 3.11 shows the thick-
ness of oxide films grown in a 0.1 M HCl solution for two different operation modes:
The COSI mode is obtained by applying the potential on the sample prior to immer-
sion into the solution, and the ramped mode is obtained by applying the potential at the
open circuit value and gradually increasing it to the desired potential value.
The formation of oxide depends on the rate at which the voltage is applied as
well as the area of the electrode surface under a constant potential mode. The mecha-
nism by which the first few layers of oxide are formed is important in establishing the
mechanism of growth of the entire oxide film.
