Heat capacities, entropies, and Gibbs free energies of formation of low-k amorphous Si(O)CH dielectric films and implications for stability during processing

Abstract

Low-temperature heat capacities of a series of low dielectric constant amorphous films with different compositions were measured from 1.8 to 300 K using a Quantum Design Physical Property Measurement System (PPMS). By using piece wise functions to fit the heat capacities, the characteristic Debye temperatures ΘD and the standard molar entropies are determined. The standard molar entropies of these materials range from 8.8 J·K−1·mol−1 to 17.5 J·K−1·mol−1. Together with the formation enthalpies obtained by high temperature oxidative solution calorimetry in molten sodium molybdate solvent, the corresponding Gibbs free energies from elements and crystalline constituents (and gaseous products as required) are obtained. The Gibbs free energy terms of these materials are dominated by the enthalpy term rather than the entropy. These samples are thermodynamically stable at room temperature with respect to elements and the samples with oxygen incorporated are generally thermodynamically more stable than the others. However, compared to crystalline binary counterparts and gases, some of these materials possess either positive or close-to-zero Gibbs free energies of formation, indicating that they are thermodynamically metastable; while, for the rest, which are stable at ambient conditions, elevation of temperature will eventually lead to decomposition.