Functionalized silica aerogels/xerogels for low dielectric constant applications

Silica thin film xerogels have demonstrated potential as a future interlayer dielectric material exhibiting extremely low dielectric constants and demonstrating thermal and chemical stability during semiconductor processing. Studies have been conducted on two systems: triethoxyfluorosilane (TEFS) and methyltrimethoxysilane (MTMS). TEFS has been chosen because of low polarizability and small particle size of resulting gels. However, TEFS gels very rapidly and creating residual hydroxyl groups leading to water adsorption. MTMS is very hydrophobic and gels at more controlled rates offering some control of gel nanostructure. However, the particle size of MTMS can increase rapidly during processing and approach IC feature sizes. Hybrid systems of TEFS and MTMS provide a balance among gel time, hydrophobicity, and transparency, and demonstrate good dielectric properties and potentially viable process integration. To optimize these systems for IC dielectric applications, we have examined the sol-gel mechanisms of these new precursors, and have employed several experimental methods to describe the porosity, microstructure, hydrophobicity, thermal stability, refractive indices, and dielectric constants of aerogels and xerogel films.