(575c) Atomic-Scale Modeling of the Mechanical Behavior of Ultra-Low-Dielectric-Constant Mesoporous Amorphous Silica Films

High-performance microelectronic devices require ultra-low-dielectric-constant (ULK) dielectric materials in order to reduce the capacitive coupling between the interconnect lines due to increased density and larger-scale integration of transistors in small areas (on the order of 10⁹ cm^-2). All candidates for ULK dielectric materials must also satisfy certain integration requirements, such as a minimum mechanical strength, threshold of thermal and electrical breakdown, and suitability for lithographic processing during chip manufacturing. Mechanical strength is particularly important in order to retain the structural integrity of the microelectronic device under the thermomechanical loading conditions characteristic of semiconductor manufacturing processes, chip packaging, and device service. Among materials that are being developed for ULK applications, porous amorphous silicas are particularly appealing due to their compatibility with current semiconductor manufacturing technologies.

In this presentation, we report results of molecular-dynamics (MD) simulations aiming at a fundamental understanding of the physical mechanisms that control the mechanical behavior of mesoporous amorphous silica film structures with pore diameters of a few nanometers, as well as prediction of the response of such structures to various mechanical loading conditions. The MD simulations employ a realistic classical potential that includes two-body and three-body interatomic interactions. The normal-density amorphous silica structures are prepared through MD starting from a crystalline beta-cristobalite solid structure and following a thermal processing sequence that includes melting, rapid quenching, and a thermal annealing schedule. We have generated ?regular? and ?disordered? mesoporous structures through the introduction of various geometric arrangements of spherical or cylindrical pores by removal of atoms from the normal-density amorphous silica matrix and subsequent thermal annealing at the temperature of interest to ensure proper structural relaxation.

We present a systematic analysis of the mechanical response of regular mesoporous amorphous silica structures with spherical pores under applied strains within the elastic limit near room temperature; the analysis is based on isostrain MD simulations using large-size computational supercells. The elastic moduli of the mesoporous structures are computed and their structural stability under tensile and compressive straining is analyzed as a function of density and pore diameter. In addition, we calculate the mechanical properties of these mesoporous structures for various pore geometries and geometric arrangements, focusing on spherical and cylindrical pores arranged in simple cubic and hexagonal lattices, respectively, as well as disordered worm-like arrangements of cylindrical pores. Furthermore, we analyze the effects of high-temperature thermal treatment of the mesoporous amorphous structures on their structural stability and mechanical strength in correlation with the underlying microstructural evolution.