Neda Radenovi and Willem van Enckevort,
Abstract
Pyramidal hillocks are often formed during wet chemical etching of
silicon for micromechanics applications and prevent the production of a
smooth surface. The observations of silicon pyramids led to the hypothesis
that a semipermeable particle locally retards the etching, causing the
pyramid formation (J. Appl. Phys. 89 (2001) 4113). The formation of pyramids
is not unique to silicon and therefore the causes of the formation and
stability of the hillocks cannot be sought in peculiarities of silicon.
We investigated {1 0 0} NaCl etched in formamide as a model system to improve
our understanding of this phenomenon. Our in-situ and ex-situ observations
of pyramid growth, shape and density support the hypothesis of the semipermeable
particle. We have strong evidence that a masking particle of dust at the
surface is responsible for the appearance of the pyramids on the crystal
surface during etching. The size of the particle is <300 nm.