Bottom-up Modeling of the Elastic Properties of Organosilicate Glasses and their Relation to Composition and Network Def
- PDF / 332,034 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 84 Downloads / 162 Views
Bottom-up Modeling of the Elastic Properties of Organosilicate Glasses and their Relation to Composition and Network Defects Jan M. Knaup1,2,*, Han Li3,†, Joost J. Vlassak3, Efthimios Kaxiras1,2,3 1
Department of Physics, Harvard University, Cambridge MA 02138, USA Institute of Materials Science, Ecole polytechnique fédérale de Lausanne, CH-1015 Lausanne, Switzerland 3 School of Engineering and Applied Sciences, Harvard University. Cambridge MA 02138, USA * [email protected] † now at IBM Thomas J. Watson Research Center, Yorktown Heights, NY 10598, USA 2
ABSTRACT Organosilicate glasses (OSG), also known as SiCOH or carbon-doped oxide are used as low-k inter-metal dielectrics for integrated circuits. The material must fulfill two conflicting requirements: It has to have low density to reduce the dielectric constant and be mechanically stable enough to withstand mechanical stress during subsequent production steps. Experimental advances in improving their mechanical and electrical properties have not yet been theoretically examined at the ab initio level, due to the relatively large model sizes necessary for amorphous materials. We employ the density-functional based tight-binding (DFTB) method to achieve an accurate description of OSG properties at different compositions. We analyze the influence of composition and topological defects on the density and bulk modulus of non-porous OSG. We find that the dependence of density and stiffness on chemical composition is of different nature. This difference is traced to a transition between different mechanisms of elastic deformation in silica glass and in silicon hydrocarbide, which is also the reason for different sensitivity to topological defects in the two materials. INTRODUCTION The ever-increasing complexity and clock frequencies of integrated circuits (IC) lead to a demand for speeding up signal propagation between switches. The propagation time of a logic state, i.e. voltage level, is governed by wire length, wire inductance and wire capacitance. While the inductance and length are mainly influenced by the design, the capacitance of the interconnects is also governed by the dielectric constant k of the insulator around the wire. Further increase of device clock frequencies makes the use of low-k insulators necessary. One important class of such materials is organosilicate glass (OSG). Often OSG layers are made porous to further reduce the k -value, however this makes them prone to mechanical failure during subsequent manufacturing steps. While OSG are already widely employed in the manufacture of complex logic devices, the origins of their properties are not yet understood well enough at the nanometer scale to enable further knowledge-based development. Some attempts have been made to understand the atomistic structure of OSG by using empirical interatomic force fields, but they suffer from limitations in the construction of their atomistic models. For instance, Yuan et.al.[1] employed force fields that do not allow changes in the bonding topology which limits the
Data Loading...
