Question

What particular etching method would you apply to display crystal disturbances in <111> silicon and produce large sharply bounded etch pits in a relatively short time? Defend your answer.

Answer 1

To display crystal disturbances in <111> silicon, anisotropic etching should be used

This means that for a perfectly cut wafer without
a mask, the steps will start mainly at the wafer edge and etch pits
that nucleate randomly all over the wafer. When a wafer with a
mask window is etched, nucleation of steps at the wafer edge
will be suppressed such that the etch rate is reduced to a min-
imum. Steps will only be generated at spontaneous nucleated
pits and dislocations in the crystal lattice and oxygen precipi-
tates. In practice, a perfect crystal aligning will never occur and
often even a predefined off-axis cut is given. For this off-axis
cut, situation steps will be initiated within the mask opening
until all steps stop at the out-of-plane-oriented -planes de-
fined by the mask geometry