Chemistry Reference
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and perfluorocarbon anionic They have
the effect of improving the wettability of BHF. The addition of anionic surfactants does
not affect the etch rate of thermal PSG, and BSG films, whereas that of cationic
surfactant decreases the etch rate of these films. Also, the activation energy does not
change with addition of surfactants. The interruption of dissolution by surfactant
adsorption is considered to be responsible for suppressing the microroughness of the
etched surface.
In alkaline solutions, silicon oxides etch at very slow rates which allows them to
be used as masks during silicon etching in these solutions. For example, the etch rate
of thermal oxide is about 0.2 Å/s in 40% KOH at 85 °C
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and is less than 0.02 Å/s in
the standard SC-1 cleaning solution.
1013
Figure 4.8 shows that in KOH solutions the
etch rate of thermal oxide increases with concentration reaching a peak value at about
35%.
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Figure 4.9 reveals that the etch rate in TMAH solution decreases with
