Area-selective atomic layer deposition (AS-ALD) is a promising bottom-up patterning approach for fabricating conformal thin films. One of the current challenges with respect to AS-ALD is the deficiency of the surface inhibitor used for fabricating nanoscale three-dimensional structures. In this study, a vapor-deliverable small inhibitor called ethanethiol (ET) that thermally adsorbs on surfaces was used for the AS-ALD of Al2O3. The inhibitor selectively adsorbed on Co and Cu substrates but not on the SiO2 substrate, allowing for the selective deactivation of Co and Cu substrates in Al2O3 ALD. The use of dimethylaluminum isopropoxide (DMAI) as the Al precursor resulted in better inhibition than the use of trimethylaluminum (TMA). Various experimental and theoretical methods, including water contact angle measurements, spectroscopic ellipsometry, X-ray photoelectron spectroscopy, density functional theory calculations, and Monte Carlo simulations, were used to elucidate the process of AS-ALD using ET. Dimerization of the DMAI precursor is considered to be a governing factor for its high deposition selectivity, while the probability of this phenomenon is very low for the TMA precursor. The current study provides insight into the selectivity of AS-ALD from the perspective of the chemical reaction and an opportunity to improve selectivity via precursor selection.

We proposed the concept of atomic layer modulation (ALM) based on precursor chemical reactivities and steric hindrance effects to fabricate multicomponent nanofilms. Because ALM employs consecutive precursor exposures followed by exposure to a counter reactant, the composition of ALM films is determined by the molecular size and chemical reactivities of the precursors. For the demonstration, dicarbonyl-bis(5-methyl-2,4-hexanediketonato)­Ru­(II) (Carish) and trimethylaluminum (TMA) were used as Ru and Al precursors, respectively, and H2O was used as the counter reactant. Prior to the experiments, the chemical reactivity and sterically hindered physisorption of the Ru and Al precursors were theoretically calculated using density functional theory (DFT) and Monte Carlo (MC) simulations, respectively. The transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) results were highly consistent with the theoretical results, and the growth characteristics were well explained by the MC- and DFT-based reaction models. We believe that ALM could be extended to other material systems, thereby providing a different method of fabricating multicomponent nanofilms for various applications including semiconductors and nanodevices.

The adsorption of metalorganic and metal halide precursors on the SiO2 surface plays an essential role in thin-film deposition processes such as atomic layer deposition (ALD). In the case of aluminum oxide (Al2O3) films, the growth characteristics are influenced by the precursor structure, which controls both chemical reactivity and the geometrical constraints during deposition. In this work, a systematic study using a series of Al­(CH3) x Cl3–x (x = 0, 1, 2, and 3) and Al­(C y H2y+1)3 (y = 1, 2, and 3) precursors is carried out using a combination of experimental spectroscopic techniques together with density functional theory calculations and Monte Carlo simulations to analyze differences across precursor molecules. Results show that reactivity and steric hindrance mutually influence the ALD surface reaction. The increase in the number of chlorine ligands in the precursor shifts the deposition temperature higher, an effect attributed to more favorable binding of the intermediate species due to higher Lewis acidity, while differences between precursors in film growth per cycle are shown to originate from variations in adsorption activation barriers and size-dependent saturation coverage. Comparison between the theoretical and experimental results indicates that the Al­(C y H2y+1)3 precursors are favored to undergo two ligand exchange reactions upon adsorption at the surface, whereas only a single Cl-ligand exchange reaction is energetically favorable upon adsorption by the AlCl3 precursor. By pursuing the first-principles design of ALD precursors combined with experimental analysis of thin-film growth, this work enables a robust understanding of the effect of precursor chemistry on ALD processes.

The continuously increasing demand for miniaturized devices in the semiconductor industry has increased the need for ultrathin films. Atomic layer deposition (ALD) is the most favorable technique for this purpose and has attracted significant interest. Prior to experimentation, understanding the reaction mechanism of the precursor with the substrate surface is crucial. However, research on the growth mechanism of ALD is limited as compared with research on its process development. Currently, ALD reaction mechanisms are typically studied using computational methods, such as molecular dynamics. However, they are complex and focus predominantly on chemical reactions between molecules and surfaces. In this study, the ALD reaction mechanisms are investigated using Monte Carlo (MC) simulations based on a simple steric hindrance model. The physical surface reactions of the precursors are modeled using MC simulations. Therefore, the steric hindrance effect of precursor adsorption on surfaces is easily predicted using a home desktop computer without requiring significant computing resources. The proposed MC simulation models yield highly consistent results with experimental data and theoretical results obtained from density functional theory calculations. We believe that this simulation method can be a useful tool with a laptop-scale computer for researchers and students working on understanding surface reactions.

The integration of bottom-up fabrication techniques and top-down methods can overcome current limits in nanofabrication. For such integration, we propose a gradient area-selective deposition using atomic layer deposition to overcome the inherent limitation of 3D nanofabrication and demonstrate the applicability of the proposed method toward large-scale production of materials. Cp(CH3)5Ti(OMe)3 is used as a molecular surface inhibitor to prevent the growth of TiO2 film in the next atomic layer deposition process. Cp(CH3)5Ti(OMe)3 adsorption was controlled gradually in a 3D nanoscale hole to achieve gradient TiO2 growth. This resulted in the formation of perfectly seamless TiO2 films with a high-aspect-ratio hole structure. The experimental results were consistent with theoretical calculations based on density functional theory, Monte Carlo simulation, and the Johnson-Mehl-Avrami-Kolmogorov model. Since the gradient area-selective deposition TiO2 film formation is based on the fundamentals of molecular chemical and physical behaviours, this approach can be applied to other material systems in atomic layer deposition.