Chemistry Reference
In-Depth Information
Consequently, dopant concentration, crystal orientation, and defects play an imporant
role in the etching process. Addition of a diluent results in an activation energy that is
between these two ranges.
The etching in
solutions is isotropic with the etch rate of the (100)
54,103,524
surface very close to that of the (111) surface.
In 0.42% HF + 17.5%
the etch rate depends on doping concentration with the etch rate of
lightly doped materials being more than 10 times lower than that of highly doped mate-
rials (it is the opposite in alkaline solutions).
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The activation energy of lowly doped
material is 12.3kcal/mol indicating a surface-controlled process whereas that of highly
doped material is 5.15 kcal/mol indicating a diffusion-controlled process.
According to Schwartz and Robbins,
103,149
the etching of silicon in the
system follows a chemical process with two basic reaction steps. In the first step, silicon
is oxidized by
which is followed by dissolution of the oxidized Si by HF. The
overall reaction is
