Low-Dielectric, Nanoporous Organosilicate Films Prepared via Inorganic/Organic Polymer Hybrid Templates

Abstract

Dielectric insulator materials containing nanometer-scale closed-cell pores with low dielectric constants ( k < 2.2), good mechanical properties, and high dielectric breakdown strengths are required for future semiconductor devices. In this paper we present a novel method for preparing nanoporous polyorganosilicate films, which promise to satisfy the key requirements, via inorganic/organic polymer hybrid templating. The nanometer-scale inorganic/organic polymer hybrids are generated in situ upon heating mixtures of methylsilsesquioxane (MSSQ) prepolymer with star-shaped hydroxy-terminated poly(ε-caprolactone) (PCL) to ∼250 °C, causing chain extension and cross-linking of MSSQ. Subsequent heating to 430 °C results in the thermal decomposition and volatilization of PCL components from the vitrified poly(methylsilsesquioxane) (PMSSQ) matrix, leaving behind porous PMSSQ films with pores with the size and shape of the original hybrid morphology. A dielectric constant as low as 2.1 has been achieved for closed-cell nanoporous PMSSQ films with hydrophobic surfaces and excellent breakdown strengths close to that of SiO 2 . Moreover, conductance measurements on inorganic/organic polymer hybrids offer insight into the development of interconnected PCL domains as the PCL content is increased above ∼25%.