Void shape evolution and formation of silicon-on-nothing structures during hydrogen annealing of hole arrays on Si(001)

Abstract

We have studied the structural evolution of voids in the Si substrate and the formation of silicon-on-nothing (SON) structures upon spontaneous reshaping of square arrays of cylindrical holes on Si(001) substrates by hydrogen annealing. Vertically elongated voids covered with {111}, {100}, {110}, and {113} facets are initially formed by the closure of the hole inlets. This step is followed by volume preserving shape changes of the faceted voids in the bulk Si. In situations where the hole-hole separation is sufficiently small, void coalescence occurs due to the shape changes of individual voids, leading to the formation of a SON structure. Until void coalescence, the shapes of individual voids change without being affected by the adjacent voids. Numerical simulations of the shape change of a completely faceted void via solely surface diffusion have been performed and have reproduced the observed shape change.