E. van Veenendaal, A. J. Nijdam and J. van Suchtelen
Abstract
We present a simulation tool for the prediction of the evolution of
macroscopic crystal growth and etching shapes that can be represented in
a two-dimensional setting. It is assumed that the advance rate of the crystal
surface depends solely on the surface orientation, which implies that the
classical kinematic wave theory applies. We present an algorithm to calculate
the crystal shape at any given point in time in a single time step for
initial crystal shapes that are either completely convex or completely
concave. We show that calculation of the crystal shape for mixed convex/concave
crystal shapes may require a series of time steps. Boundary conditions
imposed at imperfections in the crystal surface or at boundaries with a
container wall or a mask are treated. The possibility of two or more disconnected
crystal shapes that meet at some point in their evolution is also taken
into account. The simulation tool is used to predict crystal shape evolution
for the technologically relevant case of wet chemical etching of masked
silicon {1 0 0} wafers with multiple mask openings. It is shown that the
experimental evolution of Si{1 1 0} surfaces cannot be reproduced using
any simulation tool based on the assumption that the etch rate depends
solely on the surface orientation. The differences between experiments
and simulations are explained on the basis of the etching mechanism of
Si{1 1 0} surfaces.