ASD 2026 Session ASD-TuP: Area Selective Deposition Poster Session

References:
[1] Mater. Horiz., 2025, 12, 1711–1725

[2] Nat. Commun. 2016, 7, 12654.

[3] Nat. Chem. 2014, 6, 409-414.

[4]Chem. Sci., 2024,15, 2480-2485

[5] J. Am. Chem. Soc. 2025, 147, 7, 5624–5631

Although ethanol is not the strongest inhibitor reported for area selective ALD, it is well suited as a model molecule for studying surface dependent inhibition behavior. Its simple molecular structure allows systematic investigation of inhibitor induced nucleation delay without introducing additional steric or chemical complexity.

In this study, density functional theory (DFT) calculations were used to analyze the adsorption behavior of ethanol on SiO₂ and TiN surfaces. The simulations indicate a preference for EtOH adsorption on hydroxyl terminated SiO₂ surfaces, where hydrogen bonding interactions stabilize physisorbed EtOH and effectively passivate reactive –OH sites. This passivation is expected to hinder chemisorption of the molybdenum precursor, thereby suppressing nucleation on SiO₂. In contrast, the DFT results show that EtOH interacts weakly with TiN surfaces due to the absence of hydroxyl termination and the metallic nature of the substrate, leading to unstable adsorption and easily desorption.

Area-selective atomic layer deposition (AS-ALD) has emerged as a key strategy for nanoscale patterning in advanced material design complementing conventional lithography processes. However, achieving high selectivity and process reliability requires precise control of the surface chemistry. As this property is challenging to probe experimentally with atomic-level resolution, computational approaches are used to reveal the fundamental mechanisms governing selectivity. Such insights enable predictive tuning of inhibitor and precursor chemistry as well as substrate functionalization, guiding the rational design of selective deposition processes.

For inhibitor based AS-ALD several studies investigating the interactions of the inhibitor with the non-growth surface are available. [1] However, comprehensive investigations of interactions between precursor molecules and the blocking layer are still sparsely available as a realistic model for the blocking layer must be derived at first. With the present work we want to highlight the currently available approaches to derive realistic blocking layer models.These approaches span a wide range of size scales and balance accuracy against computational cost. Density functional theory (DFT) is frequently employed to identify the most stable blocking layer configurations with high accuracy. However, its use is typically restricted to a small number of structural variations and relatively small surface cells, which limits direct comparison to experimental coverages and defect structures. Random sequential adsorption (RSA) simulations provide an extremely fast way to generate inhibitor layers models on large surface models containing hundreds to thousands of adsorbates. As RSA simulations naturally sample many distinct packing motifs on extended surfaces, they are often closest to experiment. Still, RSA simulations rely on the quality and physical realism of the initial input parameters. More recently, machine-learning potentials (MLP) have enabled molecular dynamics and metadynamics simulations that are orders of magnitude faster than DFT while approaching DFT accuracy when trained on suitable reference data. These approaches enable us to explore the dynamical evolution and restructuring of blocking layers on large systems and timescales, albeit at higher cost than static RSA simulations. We firmly believe that the interplay of all three methods will enable efficient as well as accurate modelling of interactions between precursors and blocking layers in future investigations.

References

1. F. Pieck, R. Tonner-Zech, Chem. Mater. 2025, 37, 2979-3021, DOI: 10.1021/acs.chemmater.4c03477.

In this work, we demonstrate the ASD of TiO₂ dielectric thin films on MoO₂ using O₂ as a reactant. O₂ molecules are dissociated by a catalytic reaction on the MoO₂ surface, providing local active sites and enabling the adsorption of the Ti precursor and the growth of TiO₂. [2], [3] Additionally, oxygen transport can occur when two oxides with different oxygen chemical potentials form a heterogeneous interface, thereby facilitating crystallization or accelerating TiO₂ growth. [4], [5] Therefore, using O₂, a milder oxidant than O₃, can form oxygen-deficient TiO₂, which facilitates internal oxygen transfer from MoO₂ to TiO₂ during the deposition process, and consequently induces facile growth of TiO₂. We deposited TiO₂ thin films on SiO₂ and MoO₂ using O₂, and obtained a selectivity of 0.95 on MoO₂ at 320 °C. The suppressed growth on SiO₂ indicates that the reaction between the Ti precursor and the O₂ reactant was suppressed. When TiO₂ was deposited using O₂ as the reactant, the oxidation state of MoO₂ was found to be reduced compared with deposition using O₃ as the reactant, as evidenced by X-ray photoelectron spectroscopy surface analysis. These results suggest that using O₂ as a reactant facilitated oxygen transport from MoO₂ to TiO₂.

References [1] J. Mater. Chem. C 10, 36 12957 (2022), [2] Phys. Chem. Chem. Phys. 19, 43, 29244 (2017), [3] Chem. Eng. J. 488, 150760 (2024), [4] Nat. Commun. 11, 1401 (2020), [5] J. Mater. Chem. C 2, 46, 9993 (2014)

Dynamic random access memory (DRAM) continues to scale toward higher density and performance.[1] To sustain sufficient capacitance, DRAM capacitors increasingly adopt high-aspect-ratio structures while both metal and insulator layers are thinned.[2] This trend significantly raises the difficulty of conventional lithography-based patterning, motivating alternative patterning approaches such as area-selective deposition (ASD) and atomic layer etching.

Molybdenum dioxide (MoO₂) has emerged as a promising electrode material. MoO₂ has a high work function of ~5.8 eV, which is higher than that of the currently used TiN (~4.5 eV), offering potential for improved leakage current suppression. Moreover, as a conductive oxide, it can provide a more stable interface with metal oxide dielectrics. It is also compatible with rutile-phase TiO₂, a higher-k dielectric candidate than the currently used ZrO₂. In particular, rutile TiO₂ exhibits low lattice mismatch withMoO₂ on TiN, suggesting that rutile-phase formation—despite rutile being the high-temperature stable phase— promoted during the ALD process without an additional annealing step.As storage-node spacing continues to shrink, unintended deposition on surrounding SiO₂ can create parasitic conductive pathways and electrical shorts. Therefore, selective growth of the MoO₂ electrodeon TiN-defined regions is essential.

In this study, we investigate EtOH-inhibited area-selective atomic layer deposition process of MoO₂. Ethanol (EtOH) can serve as an inhibitor for ASD by suppressing precursor adsorption.The experiments were performed on TiN and SiO₂ substrates using O3 as the reactant. The deposited film initially formed as MoO_x and was converted to MoO₂ via post-deposition annealing in an N₂/O₂ (5%) ambient, as confirmed by X-ray diffraction (XRD). With EtOH inhibition, clear selectivity between TiN and SiO₂ was achieved: MoO₂ grew preferentially on TiN while remaining suppressed on SiO₂, maintaining selectivity of XX up to XX-nanometers. We also investigated Mo precursor chemisorption behavior difference in TiN and SiO₂ using DFT calculation. On SiO₂, the -OH group of EtOH reacts with surface -OH groups to form strong bonds, which hinder subsequent precursor adsorption. In contrast, on metallic surfaces EtOH forms relatively unstable bonds and can readily desorb.

These results suggest a pathway to self-aligned MoO₂ electrode formation and subsequent implementation of high-k rutile TiO₂ in metal–insulator–metal DRAM capacitors.

References

[1] W.Lee et al., J. Mater. Chem. C, 6(2018), 13250

[2] S. E. Kimet al., Adv Mater Technol, 28 (2023)

[3] Y. W. Kim et al., J Mater Chem C Mater,10 (2022), 12957

Over the last fifteen years, area-selective deposition (ASD) has emerged as a transformative approach for semiconductor manufacturing, enabling reductions in process steps, minimizing lithography requirements, and improving pattern fidelity by eliminating overlay errors. ASD also facilitates precise material deposition in complex three-dimensional structures, including vertical and horizontal trenches and vias, where conventional lithographic techniques often fail.

In this study, we focus on silicon-based inhibitors as a means of surface passivation prior to selective deposition. Although the use of alkoxysilane and chlorosilane self-assembled monolayers (SAMs) and aminosilane small-molecule inhibitors (SMIs) on silicon dioxide is well established, significant uncertainties persist regarding their behavior on the heterogeneous surfaces encountered in advanced device integration. Our discussion addresses inhibitor interactions with non-silicon oxides (Al, Ti, Hf, Ta, W), metals (Cu, Ru), and semiconductors (Si, SiGe), as well as the thermal stability and robustness of these passivation layers under processing conditions.

As ULSI scaling advances, interconnect resistance in logic and 3D-NAND devices continues to increase, and Mo is attracting attention as a potential alternative to Cu and W. For practical integration, Mo must be filled into high-aspect-ratio features under process temperature constraints (≤400 °C for logic and ≤600 °C for 3D-NAND). Atomic layer deposition (ALD) is well known for its excellent conformality; however, to avoid seam formation and to promote larger grain growth, bottom-up deposition is preferred. With the goal of realizing bottom-up filling by suppressing growth near the trench opening, we investigate the effect of NH₃ addition in Mo ALD using Mo(CO)₆ as the precursor.

Molecular dynamics (MD) simulations employing a machine-learning potential (PFP; Preferred Potential by Matlantis) suggest a strong dependence of Mo(CO)₆ adsorption on the surface termination of Mo₂N: Mo(CO)₆ undergoes dissociative adsorption when surface N atoms are not exposed, whereas adsorption is inhibited when N atoms are exposed at the surface. Motivated by this insight, we compared the growth per cycle (GPC) between (i) cyclic Mo(CO)₆ dosing and purging without NH₃ and (ii) a conventional ALD sequence with alternating Mo(CO)₆ and NH₃ exposures. The NH₃-assisted process exhibited a GPC that was approximately one order of magnitude lower than that obtained without NH₃. This reduction is consistent with the simulation trend that N-rich surfaces hinder Mo(CO)₆ adsorption, indicating that NH₃ can act as an inhibitor through surface nitridation.

Furthermore, in Mo(CO)₆-based deposition, a clear ALD half-cycle saturation behavior is not observed, implying that reactions during the precursor exposure step proceed in a CVD-like manner. NH₃ exposure is therefore expected to modify (nitridize) the surface and suppress subsequent precursor uptake. These findings suggest a route to bottom-up filling by controlling NH₃ delivery such that the degree of nitridation decays from the trench top toward the bottom, thereby preferentially suppressing growth near the opening. Experimentally, we have confirmed bottom-up growth in an ALD process using Mo(CO)₆ and NH₃, and we plan to further validate the underlying kinetics and establish the appropriate process window.

Two-dimensional (2D) van der Waals (vdW) materials are interesting for a variety of applications ranging from optoelectronics and photocatalysis to energy storage and topological devices. However, vdW materials synthesized using common techniques like chemical or physical vapor deposition often have a high density of growth-related defects: ranging from grain boundaries and twin defects to pyramidal growth and spiral defects. While pyramidal growth can be minimized through higher growth temperatures, grain boundaries, twin defects, and spiral defects are much harder to overcome.For many applications, especially in electronics and optics, these defects lead to non-radiative recombination, electron scattering, and other undesirable effects. Furthermore, the fabrication of 2D materials into quantum dots (QDs) through bottom-up wet chemistry faces problems with precise location placement and polydispersity in the QDs diameters. This makes the QDs difficult to characterize and is not ideal for most quantum computing and optical setups. Top-down nanofabrication approaches fix this issue but often causes significant damage to the surfaces or edges of the materials. To address these issues, we used selective area epitaxy (SAE) to grow Bi₂Se₃ thin films. SAE is a technique in which thin films nucleate and grow in defined areas on a wafer. This is done through use of a patterned mask where growth conditions are selected such that the film will only nucleate inside the exposed pattern.

In this poster, we will describe SAE growth of Bi₂Se₃ on Al₂O₃ (001) and Si (111) substrates using a SiO₂ mask. The mask was deposited onto a 10x10mm substrate by atomic layer deposition. Etching of the SiO₂ mask was done with standard photolithography techniques and a direct write laser beam lithography system, and the SiO₂ was removed from selected areas using a wet chemical etch, resulting in micron-scale holes of various shapes and sizes. The processed substrates were then loaded into a molecular beam epitaxy chamber for growth of the Bi₂Se₃ film. First, we will look at the effects of different substrate temperatures on the selective growth of the Bi₂Se₃ thin films. Second, we will present the geometric influence of variously shaped patterns on the crystal quality of the selectively grown films. Third, we present the effect and viability of nano-scale patterns for selective growth of vdW materials. Further studies will focus on using different materials for the substrate and mask.

As semiconductortechnologyadvances toward sub-5 nm nodes, ruthenium (Ru)area-selective atomic layer deposition (AS-ALD) is of growing interestas a back-end-of-line (BEOL) interconnect metal due to its favorable scaling behavior over copper (Cu). In BEOL, silica is the dominant dielectric and intended non-growth surface, yet its formation-dependent surface chemistry and its impact on Ru nucleation remain insufficiently explored. Here, we investigate Ru ALD on native oxide SiO_x (N-SiO_x) and thermally grown SiO₂ (T-SiO₂) as model dielectric surfaces using bis(ethylcyclopentadienyl)ruthenium(II) [Ru(EtCp)₂] with an O₂ co-reactant at 200–300 ^oC. Cross-sectional scanning electron microscopy (SEM) with surface coverage analysis reveals that both surfaces exhibit intrinsically delayed nucleation, with different extentscorrelated to their surface hydroxyl (–OH) densities. The lower –OH density of T-SiO₂ results in sparse, island-like nucleation, whereas the higher –OH density of N-SiO_x promotes more uniform nucleation. Introducing a hydrogen-assisted ABC-type (Ru/O₂/H₂) sequence markedly shortens the nucleation delay, indicating that the H₂ step promotes nucleation on hydroxyl-deficient T-SiO₂, likely via insitu rehydroxylation. Furthermore, grazing-incidence X-ray diffraction (GI-XRD), atomic force microscopy (AFM), and four-point probe measurements show that these surface-dependent nucleation behaviors lead to distinct early-stage film evolution and associated Ru film properties, including phase, morphology, and resistivity. Overall, this work provides mechanistic insight into surface-chemistry-driven Ru nucleation and establishes design principles for controlling selective growth on dielectric surfaces, advancing ASD strategies for next-generation BEOL integration.

Acknowledgement

This research used the Materials Synthesis & Characterization, Nanofabrication, and Proximal Probes Facilities at the Center for Functional Nanomaterials (CFN), which is a U.S. Department of Energy Office of Science User Facilities, at Brookhaven National Laboratory under Contract No. DE-SC0012704. This research was in part supported by the Technology Innovation Program (RS-2023–00234159) funded by the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (no. 1415187652).

Area-selective atomic layer deposition (AS-ALD) is a promising technique for advanced semiconductor manufacturing, capable of replacing conventional processes like photolithography and etching to fabricate complex patterns.¹ Significant efforts have focused on developing highly selective ALD processes through surface pretreatment or process modifications, such as deposition/etching cycles.² The use of inhibitors to deactivate non-growth areas against ALD precursors and reactants has proven effective for area-selective deposition. However, the molecular size and chemical reactivity of the ALD precursors strongly affect inhibition performance. Achieving highly selective ALD processes often requires large, less reactive precursors, which exhibit lower growth rates.^3,4 While fluorine-containing surface modification materials can reduce surface energy and suppress molecule deposition, perfluoroalkyl-coated surfaces show limited inhibition performance in Al₂O₃ ALD with trimethylaluminum (TMA), a small and highly reactive precursor.⁵

In this study, a perfluoroalkylpolyether (PFPE)-substituted alkoxysilane inhibitor (inhibitor 1) was developed, exhibiting high inhibition performance for Al₂O₃ ALD using TMA as the precursor. PFPE features a flexible fluorinated structure that differs from perfluoroalkanes due to its ether moieties, which reduce steric hindrance and increase molecular rotation. The inhibitor was evaluated as follows: a monolayer was prepared by spin-coating the compound onto UV/O₃-treated silicon substrates, followed by post-annealing to remove residual solvent. After washing with fluorinated solvent, the ALD process was performed with TMA as the precursor, H₂O as the reactant, at a stage temperature of 200 °C, and a growth-per-cycle (GPC) value of 0.7 Å. The inhibition performance was measured using XPS analysis of the Al2O3 film thickness, specifically evaluating the Al/Si ratio. Inhibitor 1 maintained its performance through 50 ALD cycles. For comparison, a short perfluoroalkyl-substituted trialkoxysilane (inhibitor 2) underwent the same procedure, but its inhibition performance deteriorated after 20 cycles. Water contact angle (WCA) measurements revealed that inhibitor 1-coated surfaces were more hydrophobic (112.3°) than those coated with inhibitor 2 (107.2°). These results suggest that flexible molecular structures and high hydrophobicity are critical for achieving high inhibition performance in ALD processes using highly reactive precursors like TMA. Detailed surface profiles and insights into inhibitor development for AS-ALD processes will be presented.

With the downscaling of microelectronic devices, it is important to find efficient small molecule inhibitors (SMI) and processes to achieve selective growth between different materials on substrate surfaces. Ru is one of the promising alternatives to conventional interconnect metals, like Cu because of its better electrical performance concerning reliability and resistivity upon downscaling.^{1, 2, 3, 4} Area Selective Atomic Layer Deposition (AS-ALD) of Ru would be useful in making interconnects bottom-up inside 3D features without formation of voids. AS-ALD can also overcome challenges of conventional patterning with lithography like cost and misalignment between subsequent layers of interconnect metallizations.⁵ This study investigates pinacolborane as a SMI for the area selective ALD of Ru on native SiO₂, Pt, TiN, Co, Cu, HfO₂, and ZrO₂ surfaces. These surfaces were subjected to 8 exposures of a 10 s pulse of pinacolborane and 30 s of N₂ purging, followed by Ru film deposition using bis(cyclopentadienyl)ruthenium (RuCp₂) and O₂ at 340°C. The results from energy dispersive X-ray spectroscopy indicate that the Ru film growth is inhibited on native SiO₂, TiN, Co, Cu, HfO₂, and ZrO₂ surfaces, making them non-growth surfaces while the film grows normally on Pt, making it growth surface. It was also observed that Ru film grows on Ru surface in the presence of pinacolborane. X-ray photoelectron spectroscopy revealed the presence of boron on HfO₂ surface but not on Pt surface, after being exposed to pinacolborane. The optimization of temperature and effective pinacolborane dose is essential for achieving maximum selectivity.

References

[1] D. Z. Austin, M. A. Jenkins, D. Allman, S. Hose, D. Price, C. L. Dezelah, Chem. Mater. 2017, 29, 1107–1115.

[2] D. Gall, J. Appl. Phys.2020, 127, 050901.

[3] J. H. Moon, E. Jeong, S. Kim, T. Kim, E. Oh, K. Lee, H. Han, Y. K. Kim, Adv. Sci. 2023, 10, 2207321.

[4] J. K. Lodha, J. Meersschaut, M. Pasquali, H. Billington, S. D. Gendt, S. Armini, Nanomaterials, 2024, 14, 1212.

[5] J. Soethoudt, F. Grillo, E. A. Marques, J. R. van Ommen, Y. Tomczak, L. Nyns, S. V. Elshocht, A. Delabie. Adv. Mater. Interfaces 2018, 5, 1800870.

The optimization of metal-semiconductor (MS) junctions is a fundamental prerequisite for advancing electronic device performance. Titanium disilicide (TiSi₂) is a widely used material due to its low electrical resistivity, good chemical stability, and low Schottky barrier height at the MS interface [1]. In practice, the existence of multiple polymorphs makes it challenging to grow phase-pure films. Among these, the C54-TiSi₂ phase exhibits the desired beneficial properties; yet it is the metastable, high-resistivity C49-TiSi₂ modification that preferentially nucleates on Si substrates. The origin of C49-selective nucleation, however, remains debated [2]. We present a first-principles atomistic model of Ti adsorption on the c(4x2)Si(100) surface that highlights the key role of surface symmetry and reconstruction for the initial stages of the interfacial TiSi2 formation process [3]. Based on DFT calculations ranging from the dilute limit to a coverage of two monolayers, we identify the energetically most stable configuration as a Ti-Ti dimer pair consisting of a surface adatom and a first-subsurface interstitial. This specific pairing coincides with the local reversal of the Si(100) surface reconstruction, which creates a characteristic low-symmetry adsorption pattern that is unique to the C49-TiSi₂ phase and thereby serves as a nucleation template for C49.This model aligns with experimental observations like the Stranski-Krastanov growth mode, the preferential formation of C49-TiSi₂ despite being less favorable than the competing C54 phase, and why disrupting the surface structure via amorphization removes the nucleation template and restores thermodynamically driven growth of the latter. This atomistic perspective on phase-selective growth suggests that such surface pre-treatment could obviate the need for the C49-C54 transformation, thereby minimizing the thermal budget in the fabrication of next-generation nanoelectronic devices.

1. Zhang, S.-L.; Smith, U. J. Vac. Sci. Technol. A 2004, 22, 1361–1370.
2. Mann, R. W.; Clevenger, L. A. J. Electrochem. Soc.1994, 141, 1347.
3. Hückmann, L.; Cottom, J.; Meyer, J.; Olsson, E. Topology-Directed Silicide Formation: An Explanation for the Growth of C49-TiSi2 on the Si(100) Surface. arXiv 2026. DOI: 10.48550/arXiv.2601.10368

Area-selective atomic layer deposition (AS-ALD) is a promising bottom-up approach for enabling self-aligned patterning in semiconductor manufacturing, reducing process complexity, costs, and edge placement errors. In particular, AS-ALD of metals on dielectric surfaces (MoD) is gaining increasing attention for advanced interconnect applications, such as middle-of-line and back-end-of-line. The AS-ALD MoD process enables metal deposition on a target dielectric surface while blocking growth on other metal or dielectric surfaces. However, achieving selectivity between chemically similar dielectric surfaces – MoD/D (metal-on-dielectric with a non-growth dielectric area) remains highly challenging due to their comparable surface terminations, surface energies, and reactivity toward metal precursors.

In this study, we explore the selective deposition of Ru on SiO₂ versus Al₂O₃ surfaces using an aldehyde-based inhibitor, butyraldehyde (BTA), and a new Ru precursor, C₄H₆Ru(CO)₃. The results reveal selective Ru growth on SiO₂, but not on the BTA-inhibited Al₂O₃ surface. Interestingly, the aldehyde-based inhibitor was previously reported to adsorb on nitride surfaces but not on hydroxyl-terminated oxide surfaces. The adsorption behavior of the inhibitor on various surfaces was investigated using water contact angle (WCA) and Fourier transform infrared spectroscopy (FTIR). Selectivity was assessed through ellipsometry, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). This work introduces a new approach for AS-ALD of MoD/D and self-aligned Ru patterning for next-generation semiconductor fabrication.

The advent of vapor phase infiltration (VPI) and related techniques has introduced a powerful method for the incorporation of inorganic materials with nanoscale precision, offering capabilities that are difficult to achieve with conventional lithography or deposition approaches. In particular, these techniques are highly relevant for the processing of semiconductor-based quantum devices, whose performance critically depends on their exceptional pattern quality.

Therefore, we combine advanced lithographic processes with VPI to selectively incorporate binary oxides into established polymeric materials, thereby enhancing pattern definition. This selective infiltration method results in hybrid organic-inorganic structures with improved line edge roughness (LER) and lower dry etch rates than conventional photoresists. By using plasma ashing after the VPI step, we may remove the organic fraction from these hybrid structures and convert them to fully inorganic oxide features that act as robust hard masks for high-fidelity pattern transfer.

In this work, we investigate VPI of Al₂O₃ in two technologically relevant thin-film platforms: (i) PS–b–PMMA block copolymers (BCP) used for bottom–up pattern formation and (ii) pre–patterned resists generated by electron beam lithography, representative of top–down lithographic processes. In BCP systems, nanoscale ordering is achieved through self-assembly and further alignment using directed self-assembly (DSA) processes on lithographically defined patterns (Fig. S1). VPI of aluminum oxide takes place selectively in the PMMA nanodomains of the films (Fig. S2), which allows us to generate hybrid or oxide structures of great interest to high-resolution, low-LER patterning.

Across both systems, we perform a systematic study of the infiltration kinetics, comparing precursor uptake, saturation behavior, and infiltration depth between homopolymers and nanostructured BCP domains with different morphologies. These measurements provide insight into how polymer chemistry, domain confinement, and pattern geometry control VPI growth.

The area selective deposition (ASD) of aluminum oxide on multiply substrates is investigated with highly selective processes observed for both dielectric on dielectric (DoD) and dielectric on metal (DoM). Selectivity is achieved without the use of inhibitors on native oxide surfaces via precursor reactivity and oxidant choice. Using the same precursor selectivity for DoD or DoM can be achieved based on the choice of oxidant. Here we showcase how a small process change can lead to the complete inversion of selectivity. Mechanisms based on surface termination are explored to describe the underlining fundamentals behind the reversibility of selectivity.

The integration of two-dimensional (2D) semiconductors into Si-CMOS technology offers a promising pathway for next-generation nanoelectronics. However, achieving precise spatial control of 2D material synthesis, which is critical for scalability and device integration, remains a fundamental challenge. Area-selective chemical vapor deposition (CVD) addresses this need by enabling location-on-demand synthesis; however, systematic engineering of synthesis processes to achieve reproducible device-grade structures remains largely unexplored. This work advances area-selective CVD through rational two-stage optimization of precursor engineering and CVD parameters, establishing a viable approach for scalable, spatially controlled synthesis of 2D heterostructures.

We engineer MoO₃ precursor thickness through electron-beam evaporation followed by wet chemical etching. Quantitative AFM analysis reveals power-law dissolution kinetics, enabling deterministic control of the optimal precursor window with excellent reproducibility. This engineered area-selective seed layer undergoes sulfurization in a two-zone CVD furnace. Through systematic parameter optimization, we identify two critical control mechanisms: (1) Sulfur precursor saturation, where increasing carrier-gas flow at optimized temperature enhances MoS₂ coverage to a saturation regime and further flow increases yield negligible change. (2) Molybdenum temperature dominance, where optimizing the Mo precursor temperature produces a five-fold enhancement in MoS₂ lateral width, extending domain dimensions above 10 μm.

We demonstrate location-selective synthesis through multiple patterned architectures: arrays of MoS₂, transmission line model (TLM) structures, and complex designs including text and Hilbert curve motifs. Optimized synthesis yields reproducible MoS₂/α-MoO₃ heterostructures with precise spatial control and excellent pattern fidelity. Raman spectroscopy confirms MoS₂ formation and reveals that amorphous MoO₃ crystallizes to α-MoO₃ during CVD, creating a functional interfacial dielectric layer.

While Atomic Layer Deposition is the most popular process for Area Selective Deposition (ASD), in this work a plasma-enhanced chemical vapor deposition (PECVD) process is employed to selectively deposit a silicon-based film on metal oxide resist (MOR), silicon, and silicon dioxide surfaces while suppressing deposition on an organic planarization layer (OPL) carbon surface. With this (PECVD) process, selective growth is observed during the initial 20 seconds of the process, after which selectivity degrades and silicon deposition on the carbon surface begins as shown in (Figure 1). Furthermore, it has been found that the selectively deposited thickness is enhanced at reduced process pressures for deposition times below 30 seconds. This time dependent (ASD) by (PECVD) process has already been observed in previous publication [1-2] and the mechanisms behind this selectivity improvement for short time of process will be discussed based on an understanding of plasma/surface interactions based on in-situ and ex-situ characterization of the plasma and the materials.

References

[1] M.Matsui, M. Miura, and K. Kuwahara, J. Vac. Sci. Technol. A 41, 063002 (2023)

[2] R.A. Robert, K. Lutker-Lee, and C. Vallée, J. Vac. Sci. Technol. A 43, 023407 (2025)

As BEOL technology scales into the sub–2–nm regime, via resistance (Rc) reduction in copper barrier–seed (CuBS) integration becomes increasingly challenging. Selective self–assembled monolayers (SAMs) have emerged as an effective approach to suppress unwanted bottom barrier and liner growth, enabling significant via Rc improvement. However, continued via dimension scaling requires further enhancement in SAM selectivity while maintaining robust removal behavior and dielectric compatibility.

This work presents an advanced SAM–enabled integration scheme designed to support further via Rc reduction in scaled BEOL interconnects. The developed SAM demonstrates improved metal selectivity relative to a production–like baseline, enabling more effective suppression of bottom barrier and liner deposition. Integration compatibility is evaluated across multiple metal substrates relevant to advanced BEOL applications.

Structural and surface analyses confirm reduced interfacial growth and effective SAM removal with minimal residual contamination. Electrical testing shows via resistance performance comparable to prior high–selectivity solutions and approximately 50% - 55% improvement relative to a non–SAM reference, with improved resistance distribution under optimized conditions. Overall, this approach provides a scalable and manufacturable pathway for continued via Rc reduction in advanced BEOL Cu interconnects.

With the continued shrinkage of critical dimension (CD) and increase of aspect ratio (AR) of interconnect, the Cu gapfill and reduction of via resistance are becoming more and more challenging for Back-End of Line (BEOL) process. Advanced RuCo binary liner improves Cu gap fill performance in advanced node structures. Selective barrier with self-assembled monolayer (SAM), which is integrated in Cu Barrier Seed process, blocks the barrier growth at via bottom and reduces via Rc. In this paper, we propose a selective liner approach to further reduce the via Rc.

This work presents the selective Ru liner process which can further decrease the via Rc compared with selective barrier process. With the help of SAM, the selective Ru liner process selectively deposits Ru on via sidewall but not on via bottom. Ru on the sidewall improves Cu gapfill and no Ru on via bottom decreases via Rc. The Cu gapfill performance and via resistance reduction are achieved at the same time by selective Ru liner process.

Surface and elemental analyses with multiple blanket metal substrates and dual damascene structures confirm suppressed Ru growth on SAM. Electrical testing shows via resistance performance improvement of ~20% over benchmark selective barrier process. Integration compatibility is evaluated and certain integration challenges are identified to meet future technology scaling requirements. Overall, this selective liner approach provides a possible pathway of extending Cu Barrier Seed Integration scaling to sub 2nm node.

Two-dimensional transition-metal oxides (TMOs) are promising for electronic applications due to their stability and favorable electrical and optical properties. Among them, MoO₃ stands out for its high dielectric constant, wide band gap (~2.9 eV), and catalytic activity, enabling diverse electronic and energy-related applications. In this work, we study the role of surface topography and charge transfer on the growth mechanism of MoO₃ on well-defined graphene (Gr) surfaces: atomically flat highly oriented pyrolytic graphite (HOPG; free-standing Gr) and metal-supported Gr on Ru(0001), exhibiting a moiré superstructure where C atoms from Gr arrange in a FCC (face-centered cubic), HCP (hexagonal close-packed), and atop pattern with respect to the Ru(0001) substrate. The molybdenum trioxide was deposited by sublimation of MoO₃ powder on the substrates held at room temperature,and the oxide growth was observed using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). The MoO₃ islands on Gr/Ru(0001) nucleate at both FCC and HCP regions and are smaller than those observed on HOPG. On both substrates, the size of the MoO₃ islands and their order increase with increasing annealing temperature. A distinct height difference of MoO₃ is observed on these two substrates. The height of MoO₃ islands on Gr/Ru(0001) corresponds to single layer of MoO₃, whereas the height of the MoO₃ island on HOPG corresponds to double layer. XPS data show that Mo in the islands on HOPG is predominantly in (6+) oxidation state while on Gr/Ru(0001) at least half is reduced to (5+). Quantitative XPS analysis shows the same MoO₃ stoichiometry on both substrates, indicating a substantial charge transfer between MoO₃ islands and Gr/Ru(0001). Our results demonstrate that substrate-induced interfacial interactions and charge transfer play a decisive role in controlling the nucleation, growth mode, thickness, and electronic structure of MoO₃ on graphene-based supports, providing a pathway to tailor 2D TMO heterostructures for electronic and catalytic applications.

Figure 1. Height differences of MoO₃ on Gr/Ru(0001) (a) and HOPG (b) following annealing at 500 K. (c) Height profiles along the blue line in image (a) and the green line in image (b).