Selection Criteria for Small-Molecule Inhibitors in Area-Selective Atomic Layer Deposition: Fundamental Surface Chemistry Considerations

Competitive Adsorption of Small Molecule Inhibitors and Trimethylaluminum Precursors on the Cu(111) Surface during Area-Selective Atomic Layer Deposition: A GCMC Study

In area-selective atomic layer deposition (AS-ALD), small molecule inhibitors (SMIs) play a critical role in directing surface selectivity, preventing unwanted deposition on non-growth surfaces, and enabling precise thin-film formation essential for semiconductor and advanced manufacturing processes. This study utilizes grand canonical Monte Carlo (GCMC) simulations to investigate the competitive adsorption characteristics of three SMIs─aniline, 3-hexyne, and propanethiol (PT)─alongside trimethylaluminum (TMA) precursors on a Cu(111) surface. Single-component adsorption analyses reveal that aniline attains the highest coverage among the SMIs, attributed to its strong interaction with the Cu surface; however, this coverage decreases by approximately 42% in the presence of TMA, underscoring its susceptibility to competitive adsorption effects. By contrast, 3-hexyne displays minimal alteration in adsorption when it is in competition with TMA, effectively inhibiting TMA adsorption and indicating its suitability as a robust SMI for AS-ALD. PT also demonstrates moderate inhibitory capability against TMA, although it is less effective than 3-hexyne in this regard. These findings highlight the importance of intermolecular forces and adsorption energies in determining SMI effectiveness in blocking TMA on non-growth surfaces. Mechanistic insights from this study reveal the nuanced influence of specific SMI-precursor interactions, emphasizing the necessity of selecting SMIs tailored to precursor characteristics and surface interactions. This work provides essential contributions to the rational design of SMIs in AS-ALD, with implications for improving deposition precision and optimizing AS-ALD parameters in nanomanufacturing applications.

Nanostructure fabrication by area selective deposition: a brief review

In recent years, area-selective deposition (ASD) processes have attracted increasing interest in both academia and industry due to their bottom-up nature, which can simplify current fabrication processes with improved process accuracy. Hence, more research is being conducted to both expand the toolbox of ASD processes to fabricate nanostructured materials and to understand the underlying mechanisms that impact selectivity. This article provides an overview of current developments in ASD processes, beginning with an introduction to various approaches to achieve ASD and the factors that affect selectivity between growth and non-growth surfaces, using area-selective atomic layer deposition (AS-ALD) as the main model system. Following that, we discuss several other selective deposition processes, including area-selective chemical vapor deposition, area-selective sputter deposition, and area-selective molecular beam epitaxy. Finally, we provide some examples of current applications of ASD processes and discuss the primary challenges in this field.

Area-Selective Atomic Layer Deposition of Ru Using Carbonyl-Based Precursor and Oxygen Co-Reactant: Understanding Defect Formation Mechanisms

Area selective deposition (ASD) is a promising IC fabrication technique to address misalignment issues arising in a top-down litho-etch patterning approach. ASD can enable resist tone inversion and bottom-up metallization, such as via prefill. It is achieved by promoting selective growth in the growth area (GA) while passivating the non-growth area (NGA). Nevertheless, preventing undesired particles and defect growth on the NGA is still a hurdle. This work shows the selectivity of Ru films by passivating the Si oxide NGA with self-assembled monolayers (SAMs) and small molecule inhibitors (SMIs). Ru films are deposited on the TiN GA using a metal-organic precursor tricarbonyl (trimethylenemethane) ruthenium (Ru TMM(CO)3) and O2 as a co-reactant by atomic layer deposition (ALD). This produces smooth Ru films (<0.1 nm RMS roughness) with a growth per cycle (GPC) of 1.6 Å/cycle. Minimizing the oxygen co-reactant dose is necessary to improve the ASD process selectivity due to the limited stability of the organic molecule and high reactivity of the ALD precursor, still allowing a Ru GPC of 0.95 Å/cycle. This work sheds light on Ru defect generation mechanisms on passivated areas from the detailed analysis of particle growth, coverage, and density as a function of ALD cycles. Finally, an optimized ASD of Ru is demonstrated on TiN/SiO2 3D patterned structures using dimethyl amino trimethyl silane (DMA-TMS) as SMI.

The surface chemistry of the atomic layer deposition of metal thin films

In this perspective we discuss the progress made in the mechanistic studies of the surface chemistry associated with the atomic layer deposition (ALD) of metal films and the usefulness of that knowledge for the optimization of existing film growth processes and for the design of new ones. Our focus is on the deposition of late transition metals. We start by introducing some of the main surface-sensitive techniques and approaches used in this research. We comment on the general nature of the metallorganic complexes used as precursors for these depositions, and the uniqueness that solid surfaces and the absence of liquid solvents bring to the ALD chemistry and differentiate it from what is known from metalorganic chemistry in solution. We then delve into the adsorption and thermal chemistry of those precursors, highlighting the complex and stepwise nature of the decomposition of the organic ligands that usually ensued upon their thermal activation. We discuss the criteria relevant for the selection of co-reactants to be used on the second half of the ALD cycle, with emphasis on the redox chemistry often associated with the growth of metallic films starting from complexes with metal cations. Additional considerations include the nature of the substrate and the final structural and chemical properties of the growing films, which we indicate rarely retain the homogeneous 2D structure often aimed for. We end with some general conclusions and personal thoughts about the future of this field.

Unfolding an Elusive Area-Selective Deposition Process: Atomic Layer Deposition of TiO2 and TiON on SiN vs SiO2

Area-selective atomic layer deposition (AS-ALD) processes for TiO2 and TiON on SiN as the growth area vs SiO2 as the nongrowth area are demonstrated on patterns created by state-of-the-art 300 mm semiconductor wafer fabrication. The processes consist of an in situ CF4/N2 plasma etching step that has the dual role of removing the SiN native oxide and passivating the SiO2 surface with fluorinated species, thus rendering the latter surface less reactive toward titanium tetrachloride (TiCl4) precursor. Additionally, (dimethylamino)trimethylsilane was employed as a small molecule inhibitor (SMI) to further enhance the selectivity. Virtually perfect selectivity was obtained when combining the deposition process with intermittent CF4/N2 plasma-based back-etching steps, as demonstrated by scanning and transmission electron microscopy inspections. Application-compatible thicknesses of ∼8 and ∼5 nm were obtained for thermal ALD of TiO2 and plasma ALD of TiON.

Reactive Vapor-Phase Inhibitors for Area-Selective Depositions at Tunable Critical Dimensions

Area-selective depositions (ASD) take advantage of the chemical contrast between material surfaces in device fabrication, where a film can be selectively grown by chemical vapor deposition on metal versus a dielectric, for instance, and can provide a path to nontraditional device architectures as well as the potential to improve existing device fabrication schemes. While ASD can be accessed through a variety of methods, the incorporation of reactive moieties in inhibitors presents several advantages, such as increasing thermal stability and limiting precursor diffusion into the blocking layer. Alkyne-terminated small molecule inhibitors (SMIs)─propargyl, dipropargyl, and tripropargylamine─were evaluated as metal-selective inhibitors. Modeling these SMIs provided insight into the binding mechanism, influence of sterics, and complex polymer network formed from the reaction between inhibitors consisting of alkene, aromatic, and network branchpoints. While a significant contrast in the binding of the SMIs on copper versus a dielectric was observed, residual amounts were detected on the dielectric surfaces, leading to variable ALD growth rates dependent on pattern-critical dimensions. This behavior can be controlled and utilized to direct film growth on patterns only above a critical threshold dimension; below this threshold, both the dielectric and metal features are protected. This method provides another design parameter for ASD processes and may extend its application to broader-ranging device fabrication schemes.