Structural characterization of ultra-thin (001) silicon films bonded onto (001) silicon wafers: a transmission electron microscopy study

Ultra-thin (001) silicon films (thickness less than 25 nm) directly bonded onto (001) silicon wafers have been investigated by transmission electron m icroscopy. Twist interfacial dislocations accommodate the twist between the two crystals, whereas tilt interfacial dislocations accommodate the tilt r esulting from the residual vicinality of the initial surfaces. In low-twist angle grain boundaries, twist interfacial dislocations are dissociated and no precipitates are detected. In high-twist angle grain boundaries, there is no dissociation and a high density of silicon oxide precipitates is obse rved at the interface. Tilt interfacial dislocations are pinned by these pr ecipitates, they are more mobile than precipitates. Without precipitates, t heir lines are straighter than those with precipitates, and this is especia lly when the bonded wafers are annealed at a high temperature. When no prec ipitates are present, tilt interfacial dislocations an associated by pairs, and we demonstrate that each tilt interfacial dislocations introduce a dia tomic interfacial step at the interface. (C) 2001 Elsevier Science Ltd. All rights reserved.