Ultrathin Hybrid SiAlCOH Dielectric Films through Ring-Opening Molecular Layer Deposition of Cyclic Tetrasiloxane

Molecular layer deposition (MLD) is a powerful vapor phase approach for growing thin polymer films with molecular-level thickness control. We applied the ring-opening MLD process to deposit a siloxane-alumina hybrid organic–inorganic thin film using tetramethyl-tetravinylcyclotetrasiloxane (V4D4) and trimethylaluminum (TMA) as precursors. In situ studies of this process with a quartz crystal microbalance (QCM) showed a linear mass increase with the number of MLD cycles within a processing temperature window between 120 and 200 °C. The QCM study also revealed self-limiting surface chemistry. A growth per cycle of 1.4 and 1.6 Å and a density of 1.9 and 2.2 g cm–3 were determined by X-ray reflectivity (XRR) for the V4D4/TMA film deposited at 150 and 200 °C, respectively. X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and in situ QCM were employed to analyze the structural changes and composition of the film. High-resolution transmission electron microscopy (HRTEM) was used to confirm the conformality of the obtained coatings. The grown siloxane-alumina film, even as thin as 12 nm, showed an extremely low leakage current density (lower than 5.1 × 10–8 A cm– 2 at ± 2.5 MV cm–1), a dielectric constant (k) of 4.7, and a good thermal stability after one-hour annealing in air at 1100 °C. The obtained highly conformal and thermally stable siloxane-alumina insulating film can be used as a component of field-effect transistors, flash memories, and capacitors in modern electronic systems.