(638g) Atomic-Scale Analysis of Structural and Mechanical Properties of Microporous and Mesoporous Amorphous Silicas

Porous amorphous silica films have important technological applications in various areas such as sensor and detection arrays, separation processes, and, more recently, in microelectronic devices as ultra-low-dielectric constant materials. In microelectronics, the structure of ?mesoporous? amorphous silica films (pore diameters of 5-10 nm) may create challenging materials reliability problems due to inferior mechanical strength compared to that of the more traditionally used dense amorphous silica films. Atomic-scale modeling based on molecular-dynamics (MD) simulations provides a powerful means for analyzing the structural response and associated mechanical behavior of such technologically promising mesoporous amorphous silica films. The results of such modeling are particularly important for predictions of materials reliability in current and future electronic device technologies, where nano-scale features become increasingly important.

We have carried out modeling studies aiming at the fundamental understanding of the nano-scale mechanisms that control the mechanical behavior of microporous and mesoporous, characterized by a regular array of mesopores, structures of dielectric materials and predicting the response of such structures to various mechanical loading conditions. Toward this goal, we have performed MD simulations using a realistic classical potential that includes two-body and three-body interatomic interactions for mechanistic understanding and atomic-scale deformation analysis. The normal-density amorphous silica structures are prepared through MD starting from crystalline beta-cristobalite structures and following a thermal processing sequence: melting, rapid quenching, and annealing. We have generated the microporous amorphous structures by volume expansion of the originally dense amorphous structure and the ?regular? mesoporous structures through the introduction of a regular array of spherical pores by removal of atoms; in all cases, generation of the porous structure is followed by thermal annealing at the temperature of interest to ensure proper structural relaxation.

In this presentation, we report results for the mechanical behavior of the microporous and regular mesoporous amorphous silica structures under applied strains over the range 0.1-1% at temperatures over a range of a few hundred degrees above room temperature obtained through nanosecond-scale MD simulation using large-size computational supercells. The elastic moduli and the hardness of the amorphous microporous and regular mesoporous silica structures are calculated as a function of their density. For the mesoporous structures, the analysis is carried out over a range of pore sizes and pore separation distances. Furthermore, a detailed analysis of the atomistic mechanisms of pore morphological evolution is reported in response to both compressive and tensile strains.