Temperature evolution of organosilicate glass films with organic bridges

Thin porous sol–gel organosilicate glass (OSG) films containing methylene (Me-OSG), ethylene (Et-OSG), or phenylene (Ph-OSG) bridges between Si atoms, along with terminal methyl groups, were spin-coated onto Si wafers. Porosity was generated using the Brij® L4 template. The investigation focused on examining the effects of annealing (200–1000 °C, 30 min) on the properties of the micro/mesoporous films. The changes in the properties of the films during the annealing process at different temperatures are impacted by the evaporation of solvents, condensation reactions, and destruction of the porogen (200–400 °C). Additionally, the degradation of terminal and bridging organic groups has been observed to occur within the temperature range of 200–600 °C. Finally, the films undergo densification through subsequent condensation and viscous sintering within a temperature range of 700–1000 °C. Ph-OSG films demonstrate remarkable resistance to temperatures of ∼400 °C. Additionally, these films exhibit the highest Young's Modulus (YM) and the smallest pore radius (YM ≈ 6.7 GPa and R ≈ 1 nm after 400 °C annealing). It is important to acknowledge that these materials exhibit a relatively hydrophilic nature, significant shrinkage, and higher refractive index (RI) and dielectric constant (k) compared to the Me-OSG and Et-OSG films. Me-OSG films demonstrate the highest hydrophobicity and porosity, along with minimal shrinkage, RI, and k. However, they also possess the largest pore radius (R = 1.7–2.2 nm after undergoing annealing at 400–550 °C). Modeling the concentrations of different species reveals that the predicted changes in concentrations are strongly dependent on the number of hydroxyl groups present on the surface of the pore walls. The decrease in the number and/or polarizability of OH groups leads to an increased impact of other species on the dielectric constant, resulting in higher computed values.