Mechanical properties and interface characteristics of nanoporous low-k materials

Low dielectric constant (low-k) insulator films with outstanding mechanical strength and fracture resistance are needed urgently for the new generation of ultra-large-scale integrated circuits (ULSI). In this paper, the mechanical properties of low-k materials and the adhesion strengths between these materials with silica have been analyzed by using molecular dynamics (MD) simulations. Atomistic models of two kinds of representative low-k materials [nanoporous amorphous silica (n-a-SiO2) and SiOCH] and their contact models with silica have been constructed. The mechanical strength of the n-a-SiO2 film decreased with the increase of porosity, and the relationship between the normalized elastic modulus and porosity was modeled. The modulus of the SiOCH film with -CH2- groups was enhanced compared with that without -CH2- groups, and the mechanism was discussed. Through investigations of the adhesion strengths between n-a-SiO2, SiOCH, and silica, it was shown that the adhesion strengths of the n-a-SiO2/silica interfaces decreased with porosity. The adhesion strengths of the SiOCH films with both -CH2- groups and -CH3 groups were higher than that of the SiOCH film merely with -CH3 groups.