Dislocation dynamics near film edges and corners in silicon

Abstract

The effect of film edge and corner stress fields on the behavior of dislocations in silicon is investigated. Stresses arising from a silicon–nitride film pad on a silicon substrate are calculated using the finite element method, and the resulting spatially varying stress–tensor components are utilized to drive numerical simulations of dislocation behavior. The dislocation dynamics code involves a full three-dimensional implementation of the Peach–Koehler force formalism. By studying the motion of dislocations on various slip systems in various locations relative to the nitride pad, we are able to determine the stationary dislocation configurations which can be achieved in this geometry. The zero resolved-stress contours near the silicon surface are shown to be a useful tool for understanding both the nature of the dislocation propagation as well as the final dislocation configurations. We examine the nucleation of dislocations qualitatively from the critical-radius point of view, and identify the “hot spots” for nucleation near the nitride film edge. Thicker nitride films are found to have a greater number of possible nucleation sites, and a greater variety of possible stable configurations, as experimentally observed. The simulations are extended to study the effect of changing the pad edge orientation relative to the silicon lattice. Finally, we demonstrate the usefulness and power of these techniques in handling more complex situations by illustrating the types of behavior resulting from cross-slip, reconnection between dislocations nucleated on intersecting glide planes, Frank–Read spiral sources, and traveling dislocations interacting with nitride edges.