Investigating the Impact of the Spatial Arrangement of the Terminal Methyl Group Relative to the Bridging Ethylene Group on the Properties of PMO Films

The impact of the spatial arrangement of the terminal methyl group in relation to the bridging ethylene group on the properties of PMO films has been studied using pairs of BTMSE–MTMS and TESDEMSE–MTMS precursors containing C–C bridging groups. TESDEMSE features a Si-attached CH₃ group within the same molecule, forming hydrophobic films independently of MTMS concentration. Pure BTMSE-based films are hydrophilic and exhibit an increased dielectric constant due to water adsorption. The addition of MTMS to BTMSE introduces CH₃ into the films, rendering them hydrophobic. The spatial arrangement of CH₃ relative to C–C significantly affects hydrophobicity, dielectric properties, thermal stability, and porosity. The mechanical properties of the films also depend on the location of CH₃ groups. TESDEMSE demonstrates potential as a single precursor for low-k film deposition. However, annealing (curing) at 430 °C reduces the concentration of C–C bonds, and this phenomenon is more pronounced in TESDEMSE-based films. Quantum chemical analysis indicates that the ethylene bridge is generally weaker than the terminal methyl group, with the presence of an adjacent methyl group further decreasing its stability. The low thermal stability of these films poses a challenge for certain practical applications.