Abstract: On Si{100} surfaces etched in anisotropic etchants such
as aqueous solutions KOH and TMAH, pyramidal etch hillocks are frequently
found. Besides these hillocks, we have investigated hillocks that have
partially disappeared using scanning electron microscopy (SEM). During
re-etching numerous additional pyramidal etch hillocks are formed on the
exact spots where SEM pictures were made earlier. These observations suggest
that semipermeable particles adhering to the surface are responsible for
the development of the pyramidal etch hillocks. In order to investigate
the influence of such nanometer scale particles on the etch rate and the
surface morphology, Monte Carlo simulations were performed of etching of
Si{100} surfaces on which small semimasks are present. The presence of
the microscopic semimasks is shown to cause the formation of macroscopic
hillocks, which closely resemble experimentally observed hillocks. Removal
of the semimask on top of a hillock leads to a vanishing pyramidal etch
hillock. In the Monte Carlo model, however, the etch rate as a function
of surface orientation has a maximum for {100}, while in reality {100}
corresponds to a local minimum. This implies that for typical experimental
conditions an etch hillock should not be stable despite a semipermeable
particle on top, because of underetching starting from < 110 > ridges
of the hillock. This paradox can be resolved by assuming that the ridges
act as sinks of tiny particles. This gives a reduction in etch rate of
the ridges, next to the top, which is necessary for the hillock to remain
stable. The exact nature of these masking particles is unknown, but silicate
particles are a likely candidate. (C) 2001 American Institute of Physics.