Chemistry Reference
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stoichiometric due to the incorporation of a significant amount of hydroxyl ions and
water in the oxide. Silicon oxide that contains a high concentration of hydroxyl ions
has a fast etch rate.
427
It has been found that a thermal oxide can be injected with
hydroxyl ions under an anodic potential forming a hydrated surface layer. The hydrated
layer etches much faster than the thermal oxide underneath as shown in Fig. 4.12.
427
Thus, the high etch rates of anodic oxides may be partly attributed to the loose struc-
ture and partly to the high degree of hydration. Similar to CVD films, anodic oxides
can be dandified, resulting in lower etch rates. Figure 4.28 shows that the etch rate of
anodic oxide films formed at
in 0.05% HF solution greatly decreases with increas-
ing annealing temperature.
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