Porous amorphous silica films are among the most promising materials to satisfy the ultra-low-dielectric-constant (k) requirements for dielectrics to be used in high-density microelectronic devices with nano-scale feature sizes. Due to the low density of “mesoporous” amorphous silica films with pore diameters of 5-10 nm, however, such ultra-low-k dielectric materials have considerably weaker elastic modulus, hardness, and mechanical strength compared to those of the more traditionally used dense amorphous silica films. These inferior mechanical properties of the porous silica films threaten the structural integrity of microelectronic devices and create challenging materials reliability problems. At the nano-scale feature size, 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 significant mesoporous amorphous materials. The results of MD simulation have important implications regarding the structural optimization of porous dielectric materials and assessment of materials reliability in future generations of microelectronic devices.

In this presentation, we report results of MD simulations aiming at fundamental understanding of the nano-scale mechanisms that control the mechanical behavior of mesoporous amorphous silica film structures and predicting 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 structure and following a thermal processing sequence: melting, rapid quenching, and a thermal annealing schedule. We have generated “regular” mesoporous structures through the introduction of a regular array of spherical pores by removal of atoms from the normal-density amorphous silica matrix; generation of the mesoporous amorphous material is followed by thermal annealing at the temperature of interest to ensure proper structural relaxation.

A systematic analysis is presented of the mechanical behavior of regular mesoporous amorphous silica structures under applied strains within the elastic limits near room temperature based on nanosecond-scale MD simulation using large-size computational supercells. The elastic moduli and the hardness of the regular mesoporous amorphous silica structures are computed and their elastic and structural stability are examined as a function of density and pore size. Furthermore, effects on the structural stability and mechanical properties of residual stresses in the mesoporous structures are estimated. The results of this computational study are compared with experimental measurements of mechanical properties on specifically manufactured mesoporous amorphous silica films with structures and densities compatible with our MD simulation models.

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