Identification of stable boron clusters in c-Si using tight-binding statics

Abstract

As a particularly important p-type dopant, boron exhibits some problematical phenomena during the fabrication of microelectronic devices, especially transient enhanced diffusion (TED) following ion implantation and annealing. TED is due, in large part, to the formation of boron-defect clusters. This article describes a search for particularly stable boron-defect clusters (up to B4I4). A tight-binding method, in conjunction with atomic-scale statics calculations, is used to study boron and boron-defect clusters containing up to four boron atoms and four self-interstitials within a matrix of crystalline silicon. Formation and binding energies are reported for these species. There is a tendency to form a four-atom ring containing two Si self-interstitials and two boron atoms. One guiding principle for the stability of the geometry of the clusters is to maximize the number of unstrained bonds (i.e. with Si-like bond lengths); the higher the extent of unstrained bonds, the lower the formation energy. Symmetry is found to play a smaller role in determining preferred structures.