Stepwise mechanism and H2O-assisted hydrolysis in atomic layer deposition of SiO2 without a catalyst

Growth Mechanism, Ambient Stability, and Charge Trapping Ability of Ti-Based Maleic Acid Hybrid Films by Molecular Layer Deposition

Ti-based maleic acid (MA) hybrid films were successfully fabricated by molecular layer deposition (MLD) using organic precursor MA and inorganic precursor TiCl₄. The effect of deposition temperature on the growth rate, composition, and bonding mode of hybrid thin films has been investigated systematically. With increasing temperature from 140 to 280 °C, the growth rate decreases from 1.42 to 0.16 Å per MLD cycle with basically unchanged composition ratio of C:O:Ti in the films. Fourier transform infrared spectra indicate that all hybrid films show preference for bidentate bonding mode. Further analyses of X-ray photoelectron spectroscopy and in situ quartz crystal microbalance elucidate that as-deposited MLD Ti-MA hybrid films consist of inorganic Ti-O-Ti units and organic-inorganic Ti-MA units. In addition, the density functional theory calculation was performed to investigate the possible reaction mechanism of the TiCl₄-MA MLD process, which is well consistent with experimental results. More importantly, upon comparison with the TiCl₄-fumaric acid MLD system, it is demonstrated that the cis- and trans-configurations of butenedioic acid influence the MLD growth, bonding mode, stability, and charging ability of MLD hybrid films. Ti-MA hybrid films exhibit better stability and charging ability than Ti-FA hybrid films, benefiting from the inorganic Ti-O-Ti units in the hybrid films.

Catalyzed Atomic Layer Deposition of Silicon Oxide at Ultralow Temperature Using Alkylamine

We report the catalyzed atomic layer deposition (ALD) of silicon oxide using Si₂Cl₆, H₂O, and various alkylamines. The density functional theory (DFT) calculations using the periodic slab model of the SiO₂ surface were performed for the selection of alternative Lewis base catalysts with high catalytic activities. During the first half-reaction, the catalysts with less steric hindrance such as pyridine would be more effective than bulky alkylamines despite lower nucleophilicity. On the other hand, during the second half-reaction, the catalysts with a high nucleophilicity such as triethylamine (Et₃N) would be more efficient because the steric hindrance is less critical. The in situ process monitoring shows that the calculated atomic charge is a good indicator for expecting the catalyst activity in the ALD reaction. The use of Et₃N in the second half-reaction was essential to improving the growth rate as well as the step coverage of the film because the Et₃N-catalyzed process deposited a SiO₂ film with a step coverage of 98% that is better than 93% of the pyridine-catalyzed process. The adsorption of pyridine, ammonia (NH₃), or trimethylamine (Me₃N) salts was more favorable than that of Et₃N, n-Pr₃N, or ⁱPr₃N salts. Therefore, Et₃N was expected to incorporate less amine salts in the film as compared to pyridine, and the compositional analyses confirmed that the concentrations of Cl and N by the Et₃N-catalyzed process were significantly lower than those by the pyridine-catalyzed process.