Energetics of porous amorphous low-k SiOCH dielectric films

The trend toward dimension reduction in electronic devices has driven the research and development of low dielectric constant materials to solve resistance capacitance delays and power consumption issues. Amorphous porous hydrogenated silicon oxycarbides form a class of materials that have even lower dielectric constants than other silicon oxycarbides, achieved by introducing organic functional groups as well as porosity to alter the structure and decrease the density of conventional silica. However, these films tend to decompose to SiO₂ during thermal annealing and nano-electronic fabrication processes. This apparent instability leads to the need to investigate how porosity can change the fundamental thermodynamic stability of this class of materials. We used high temperature oxidative molten salt solution calorimetry and cryogenic heat capacity measurements to directly determine enthalpies of formation, heat capacities, and standard entropies of a series of well-characterized porous SiOCH films. Thus, a full thermodynamic dataset has been obtained for these porous low-k films. All of these samples are either found to be unstable or metastable at or even below 298.15 K with respect to their crystalline counterparts and gaseous products. Thus, there appears little chance of forming thermodynamically stable amorphous porous SiOCH films and their persistence in fabrication and use is controlled by kinetic rather than thermodynamic factors.