Area-selective Atomic Layer Deposition Research Articles

In situ formation of inhibitor species through catalytic surface reactions during area-selective atomic layer deposition of TaN.

Small molecule inhibitors (SMIs) have been gaining attention in the field of area-selective atomic layer deposition (ALD) because they can be applied in the vapor-phase. A major challenge for SMIs is that vapor-phase application leads to a disordered inhibitor layer with lower coverage as compared to self-assembled monolayers, SAMs. A lower coverage of SMIs makes achieving high selectivity for area-selective ALD more challenging. To overcome this challenge, mechanistic understanding is required for the formation of SMI layers and the resulting precursor blocking. In this study, reflection adsorption infrared spectroscopy measurements are used to investigate the performance of aniline as an SMI. Our results show that aniline undergoes catalytic surface reactions, such as hydrogenolysis, on a Ru non-growth area at substrate temperatures above 250 °C. At these temperatures, a greatly improved selectivity is observed for area-selective TaN ALD using aniline as an inhibitor. The results suggest that catalytic surface reactions of the SMI play an important role in improving precursor blocking, likely through the formation of a more carbon-rich inhibitor layer. More prominently, catalytic surface reactions can provide a new strategy for forming inhibitor layers that are otherwise very challenging or impossible to form directly through vapor-phase application.

Selective nitride passivation using vapor-dosed aldehyde inhibitors for area-selective atomic layer deposition

We present a methodology for achieving selective deposition of Ru films through surface modification via vapor-phase functionalization of aldehyde inhibitor molecules. We conduct a comparative evaluation of the blocking capability using vapor-dosing of two different types of aldehyde molecules: undecylaldehyde and benzaldehyde as aliphatic and aromatic ring inhibitors, respectively, on W, TiN, SiN, and SiO2 substrates. By adjusting the vapor-process conditions of both aldehydes, we confirm chemo-selective adsorption on nitride surfaces, resulting in significant growth retardation during subsequent Ru atomic layer deposition. Under optimized conditions for achieving nitride versus oxide selectivity, we successfully demonstrated area-selective atomic layer deposition (AS-ALD) of Ru films on patterned-TiN/SiO2 substrates.

HfO2 Area-Selective Atomic Layer Deposition with a Carbon-Free Inhibition Layer

HfO₂ Area-Selective Atomic Layer Deposition with a Carbon-Free Inhibition Layer

Area-selective atomic layer deposition of Ru thin films by chemo-selective inhibition of alkyl aldehyde molecules on nitride surfaces

Area-selective atomic layer deposition (AS-ALD) on pre-defined areas is of crucial importance nowadays in significantly reducing complexities associated with current top-down fabrication processes. In this work, we report the effects of surface modification using various alkyl aldehyde inhibitors with different chain lengths—hexanal, decanal, and undecanal—on nitride surfaces such as TiN and SiN to achieve AS-ALD. On the basis of density functional theory calculations and experimental analysis, including water contact angle and X-ray photoelectron spectroscopy, it is evident that aldehydes would chemo-selectively react with the –NH2 functional groups present on the nitride surfaces. Then, we further investigate their blocking ability against subsequent Ru ALD, a promising next-generation electrode material. It is worth noting that the Ru deposition thickness decreased by 4–10 nm with the presence of undecanal adsorbed on SiN and TiN substrates. Finally, we successfully demonstrate AS-ALD of Ru thin films over 8 nm on a patterned TiN/SiO2 substrate. These results hold potential for applications in bottom-up nanofabrication techniques for next-generation nanoelectronic applications.

Area-selective atomic layer deposition (AS-ALD) of low temperature (300 °C) cobalt thin film using octadecyltrichlorosilane (ODTS) self-assembled monolayers (SAMs)

As the semiconductor industry advances, manufacturing technologies encounter challenges in achieving precise alignment and thickness control with smaller and more intricate 3D structures. Addressing this, Area-selective atomic layer deposition (AS-ALD) emerges as a promising “bottom-up” approach, offering an alternative to current nano-patterning techniques. To achieve AS-ALD, self-assembled monolayers (SAMs) are employed as inhibitor agents. In this study, we employed plasma-enhanced atomic layer deposition (PEALD) to promote self-limiting surface reactions and enable low-temperature processing, thereby facilitating the implementation of high purity cobalt (Co) film through AS-ALD using octadecyltrichlorosilane (ODTS) SAM as an inhibitor. The selective deposition is achieved by employing SAMs as an inhibitor, belonging to the deactivation process, a common method for realizing a bottom-up approach. SAMs can form a thin organic film on a solid surface, allowing for surface modifications to become hydrophobic or hydrophilic. Through the selective deposition of Co in the PEALD low-temperature process (300 °C), we successfully addressed the degradation issue of ODTS SAM and verified the successful achievement of a high-purity selectively deposited 13.4 nm Co film. Our findings highlight the potential of selective Co deposition for realizing complex 3D structures and narrow interconnection layers.

Blocking mechanisms in area-selective ALD by small molecule inhibitors of different sizes: Steric shielding versus chemical passivation

Small molecule inhibitors (SMIs) hold great promise for area-selective deposition due to their vapor-phase application being compatible with industrial processing. However, to date only a handful of SMIs have been studied, and the mechanisms of precursor blocking require further understanding. In this study, we explore the inhibition of SiO2 ALD on Al2O3 surfaces comparing three SMIs of different sizes: acetic acid (HAc), acetylacetone (Hacac), and 2,2,6,6-tetramethyl-3,5-heptanedione (Hthd). The goal is to unravel the contributions of two important factors to their blocking performance: steric shielding, i.e. physically covering reactive surface sites, and chemical passivation, i.e. chemically consuming surface reactive sites. Experimentally, it is found that HAc and Hthd outperform the previously studied Hacac, as revealed by longer nucleation delays on functionalized Al2O3 from in-situ spectroscopic ellipsometry, and by enhanced Si precursor blocking inferred from in-situ infrared spectroscopy. Through density functional theory and random sequential adsorption simulations, we illustrate that varying the size of SMIs brings benefits from either higher steric shielding or better chemical passivation. As compared to Hacac, HAc performs better due to its smaller size, yielding denser packing and thus higher chemical passivation. Hthd on the other hand, benefits from its bulkiness with a higher contribution from steric shielding.

Highly area-selective atomic layer deposition of device-quality Hf1-xZrxO2 thin films through catalytic local activation

Area-selective atomic layer deposition (AS-ALD) has garnered significant attention as a promising bottom-up patterning process for sub-10 nm scale technology, offering unmatched atomic-scale precision and pattern alignment capabilities in 3D nanofabrication. In this study, we present a groundbreaking methodology for achieving highly selective deposition of Hf1-xZrxO2 (HZO) thin films through catalytic local activation on noble metal surfaces (Ru and Pt) and TiN surfaces, without the need for surface inhibitory materials. To achieve inherent selectivity on metal surfaces, we employ O2 gas as a mildly oxidizing reactant and utilize cyclopentadienyl-tris(dimethylamido)-hafnium(zirconium) [Hf(Zr)Cp(NMe2)3] precursors, which require strong oxidizing agents, for HZO film formation. By catalytically dissociating O2 molecules, we successfully achieved area-selective deposition of HZO films greater than ∼7 nm on both blanket Ru versus Si substrates and Pt/Si-patterned substrates. Furthermore, we demonstrate the selective deposition of antiferroelectric HZO thin films with high dielectric constants of 34 and 31 on Ru and TiN substrates, respectively, using the inherent AS-ALD method combined with post-ozone treatment. Importantly, this catalytic local activation approach for achieving inherent deposition selectivity expands the potential utility of 3D bottom-up nanopatterning processes in next-generation nanoelectronic applications.

Area-selective atomic layer deposition on 2D monolayer lateral superlattices

The advanced patterning process is the basis of integration technology to realize the development of next-generation high-speed, low-power consumption devices. Recently, area-selective atomic layer deposition (AS-ALD), which allows the direct deposition of target materials on the desired area using a deposition barrier, has emerged as an alternative patterning process. However, the AS-ALD process remains challenging to use for the improvement of patterning resolution and selectivity. In this study, we report a superlattice-based AS-ALD (SAS-ALD) process using a two-dimensional (2D) MoS2-MoSe2 lateral superlattice as a pre-defining template. We achieved a minimum half pitch size of a sub-10 nm scale for the resulting AS-ALD on the 2D superlattice template by controlling the duration time of chemical vapor deposition (CVD) precursors. SAS-ALD introduces a mechanism that enables selectivity through the adsorption and diffusion processes of ALD precursors, distinctly different from conventional AS-ALD method. This technique facilitates selective deposition even on small pattern sizes and is compatible with the use of highly reactive precursors like trimethyl aluminum. Moreover, it allows for the selective deposition of a variety of materials, including Al2O3, HfO2, Ru, Te, and Sb2Se3.

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.

Organosulfide Inhibitor Instigated Passivation of Multiple Substrates for Area-Selective Atomic Layer Deposition of HfO2

Organosulfide Inhibitor Instigated Passivation of Multiple Substrates for Area-Selective Atomic Layer Deposition of HfO₂

Machine Learning Modeling and Run-to-Run Control of an Area-Selective Atomic Layer Deposition Spatial Reactor

Semiconducting materials require stringent design specifications that make their fabrication more difficult and prone to flaws that are costly and damaging to their computing and electrical properties. Area-selective atomic layer deposition is a process that addresses concerns associated with design imperfections but requires substantial monitoring to ensure that process regulation is maintained. This work proposes a run-to-run controller with an exponentially weighted moving average method for an area-selective atomic layer deposition rotary reactor by adjusting the rotation speed of the substrate to control the growth per cycle of the wafer, which is calculated through a multiscale model with machine learning integration for pressure field generation and kinetic Monte Carlo simulations to increase computational efficiency. Results indicate that the run-to-run controller was able to bring the process to the setpoint when subjected to moderate pressure and kinetic shift disturbances.

(Invited) Area Selective Deposition Using Homometallic Precursor Inhibitors

Area-selective atomic layer deposition (AS-ALD) is envisioned to play a key role in next-generation nanofabrication for Si devices. In this presentation, various types of precursor inhibitors studied in our group will be summarized and another opportunity of our AS-ALD will be discussed. The chemical and physical interactions of inhibitors with precursors were successfully explained through theoretical calculations by density functional theory (DFT) and Monte Carlo simulation. Another concept of selective deposition by using a homometallic precursor inhibitor was proposed for seam-less deposition inside 3D structures. The results could provide insights for the next generation nanofabrication in the semiconductor technology using ALD.

(Invited) Atomistic Insights into Continuous and Area-Selective ALD Processes: First-Principles Simulations of the Underpinning Surface Chemistry

Atomic layer deposition (ALD) is a highly advanced thin film deposition technology that has found widespread use in nanoelectronics, photovoltaics, fuel cell and recently all-solid-state battery applications. It is widely regarded as the state-of-the-art technique for producing thin films due to its exceptional conformality on high-aspect ratio structures, atomic level thickness control, and tuneable film composition. In recent years, area-selective atomic layer deposition (AS-ALD) has emerged as a promising technology for high-fidelity nano-patterning, and significant progress has been made in understanding and developing highly selective processes for various material systems. Along these lines, we have recently shown that high-throughput, low defectivity, highly selective SiO2 deposition can be achieved on various substrates by combining atmospheric-pressure spatial ALD with integrated area-deactivation using small molecule inhibitors and plasma-enhanced spatial etching [1].ALD is a surface-controlled technique that relies on the self-limiting reactions of the precursors and co-reactants with the deposition surface in alternating cycles. The initial step in ALD nucleation on the target substrate is a key factor in the deposited film quality, and efficient precursor binding on the surface is critical. Molecular dynamics (MD) simulations and minimum-energy reaction pathway analysis based on ab initio Density Functional Theory (DFT) calculations provide invaluable insights into the surface chemistry, enabling customisation of ALD processes to boost uniformity, conformality, and area-selectivity of the resulting films.In this talk, I will discuss how first-principles simulations can be used synergistically with experimental findings to achieve high-efficiency plasma-enhanced atomic-layer cleaning (ALC) of impurities from various ALD films and substrates, design proper chemical surface modifications that enable continuous and conformal ALD nucleation even on chemically-inert surfaces (like graphene), and unveil the particular surface chemistry governing high-fidelity area-selectivity with an atomic-level precision in ultrathin coatings [1-9]. By combining the insights gained from first-principles simulations with experimental techniques, we can push the frontiers of device manufacturing to new heights, opening up exciting possibilities for further technological advances in nanoelectronics, photovoltaics, fuel cell and energy storage applications.[1] Advanced Materials, Just Accepted, (DOI: 10.1002/adma.202301204); [2]Nanoscale, 2021, 13, 10092-10099; [3] Chem. Mater. 2019, 31 (4), 1250-1257.; [4] Adv. Mater. Interfaces 2018, 5 (13), 1800268.; [5] Chem. Mater. 2017, 29 (3), 921–925.; [6] ACS Nano 2017, 11 (9), 9303–9311.; [7] Sol. Energy Mater. Sol. Cells 2017, 163, 43–50.; [8] Chem. Mater. 2017, 29 (5), 2090–2100.; [9] Nanoscale 2016, 8 (47), 19829–19845. Figure 1

(Invited) Small Molecule Inhibitor-Based Approaches for Area-Selective Deposition from First Principles

Atomic layer deposition tackles ever new research questions. Area-selective deposition is one of these recent challenges. Several approaches have been developed to achieve selectivity. One of the most promising is using comparatively small molecules to block the non-growth surface while leaving the growth surface uncovered for the ALD process.This approach requires in-depth knowledge of the surface chemistry of both surfaces involved. In addition, the decomposition pathways of SMI-covered surfaces need to be uncovered to enable stable ALD growth over a maximum number of cycles.These questions are very challenging for lab-based investigations. We present recent progress in the ab initio description of key questions regarding SMI-based ALD processes. At the example of silanol-based SMIs, surface chemistry for Al2O3 growth on Cu while blocking SiO2 will be discussed and compared to experimental findings.[1] Furthermore, the importance of choosing the appropriate surface model will be highlighted. Especially for the challenging question of SMI-layer decomposition.[1 J. Yarbrough, F. Pieck, D. Grigjanis, I.-K. Oh, P. Maue, R. Tonner-Zech, S. F. Bent, "Tuning Molecular Inhibitors and Aluminum Precursors for the Area-Selective Atomic Layer Deposition of Al2O3", Chem. Mater. 2022, 34, 4646-4659.We gratefully acknowledge funding from a Merck KGaA, Darmstadt, Germany 350th Anniversary Research Award. Computations were performed on the CSC Frankfurt, HLR Stuttgart, ZIH Dresden and HPC Regensburg.Figure 1 General structure (a) of the studied SMIs with different reactive and blocking groups (b). Schematic structures of the calculated condensation reactions of the SMIs with OH groups of the SiO2 surface (c). Color code: Si (blue), O (red), and H (white). Figure 1

Machine learning-based exploration of molecular design descriptors for area-selective atomic layer deposition (AS-ALD) precursors.

Area-selective atomic layer deposition (AS-ALD) is a thin film deposition technique developed using conventional ALD by considering the surface chemical nature of the substrate. Selecting appropriate precursors is a critical step in developing an efficient AS-ALD process with high deposition selectivity. However, the current efficiency of research on viable AS-ALD precursors is limited because of the absence of theoretical design rules for precursor chemical structures. In this study, our objective is to propose molecular design principle for precursors for AS-ALD, particularly focusing on achieving high deposition selectivity of oxides on diverse substrates. Current preliminary results suggest that ML-based prediction model may provide a fundamental molecular-level understanding of the reactivity of metal oxide precursors, that can be useful for efficient selection of suitable precursors for AS-ALD. We employ density functional theory (DFT) calculations and machine learning (ML) techniques to analyze the relationship between the structure and the surface reactivity of the precursor. Considering DFT calculation data (M06L/def2-tzvp, Gaussian 09 and Orca 4.0) and information on precursor structures, artificial neural networks (ANN, neuralnet, R) are applied to identify critical descriptors of the AS-ALD process. Furthermore, we utilize this ANN model to predict precursor reactivity according to surface terminations.

Stearic Acid as an Atomic Layer Deposition Inhibitor: Spectroscopic Insights from AFM-IR.

Modern-day chip manufacturing requires precision in placing chip materials on complex and patterned structures. Area-selective atomic layer deposition (AS-ALD) is a self-aligned manufacturing technique with high precision and control, which offers cost effectiveness compared to the traditional patterning techniques. Self-assembled monolayers (SAMs) have been explored as an avenue for realizing AS-ALD, wherein surface-active sites are modified in a specific pattern via SAMs that are inert to metal deposition, enabling ALD nucleation on the substrate selectively. However, key limitations have limited the potential of AS-ALD as a patterning method. The choice of molecules for ALD blocking SAMs is sparse; furthermore, deficiency in the proper understanding of the SAM chemistry and its changes upon metal layer deposition further adds to the challenges. In this work, we have addressed the above challenges by using nanoscale infrared spectroscopy to investigate the potential of stearic acid (SA) as an ALD inhibiting SAM. We show that SA monolayers on Co and Cu substrates can inhibit ZnO ALD growth on par with other commonly used SAMs, which demonstrates its viability towards AS-ALD. We complement these measurements with AFM-IR, which is a surface-sensitive spatially resolved technique, to obtain spectral insights into the ALD-treated SAMs. The significant insight obtained from AFM-IR is that SA SAMs do not desorb or degrade with ALD, but rather undergo a change in substrate coordination modes, which can affect ALD growth on substrates.

Area-Selective Deposition by Cyclic Adsorption and Removal of 1-Nitropropane.

The ever-greater complexity of modern electronic devices requires a larger chemical toolbox to support their fabrication. Here, we explore the use of 1-nitropropane as a small molecule inhibitor (SMI) for selective atomic layer deposition (ALD) on a combination of SiO2, Cu, CuOx, and Ru substrates. Results using water contact angle goniometry, Auger electron spectroscopy, and infrared spectroscopy show that 1-nitropropane selectively chemisorbs to form a high-quality inhibition layer on Cu and CuOx at an optimized temperature of 100 °C, but not on SiO2 and Ru. When tested against Al2O3 ALD, however, a single pulse of 1-nitropropane is insufficient to block deposition on the Cu surface. Thus, a new multistep process is developed for low-temperature Al2O3 ALD that cycles through exposures of 1-nitropropane, an aluminum metalorganic precursor, and coreactants H2O and O3, allowing the SMI to be sequentially reapplied and etched. Four different Al ALD precursors were investigated: trimethylaluminum (TMA), triethylaluminum (TEA), tris(dimethylamido)aluminum (TDMAA), and dimethylaluminum isopropoxide (DMAI). The resulting area-selective ALD process enables up to 50 cycles of Al2O3 ALD on Ru but not Cu, with 98.7% selectivity using TEA, and up to 70 cycles at 97.4% selectivity using DMAI. This work introduces a new class of SMI for selective ALD at lower temperatures, which could expand selective growth schemes to biological or organic substrates where temperature instability may be a concern.

Area-Selective Atomic Layer Deposition for Resistive Random-Access Memory Devices.

Resistive random-access memory (RRAM) is a promising technology for data storage and neuromorphic computing; however, cycle-to-cycle and device-to-device variability limits its widespread adoption and high-volume manufacturability. Improving the structural accuracy of RRAM devices during fabrication can reduce these variabilities by minimizing the filamentary randomness within a device. Here, we studied area-selective atomic layer deposition (AS-ALD) of the HfO2 dielectric for the fabrication of RRAM devices with higher reliability and accuracy. Without requiring photolithography, first we demonstrated ALD of HfO2 patterns uniformly and selectively on Pt bottom electrodes for RRAM but not on the underlying SiO2/Si substrate. RRAM devices fabricated using AS-ALD showed significantly narrower operating voltage range (2.6 × improvement) and resistance states than control devices without AS-ALD, improving the overall reliability of RRAM. Irrespective of device size (1 × 1, 2 × 2, and 5 × 5 μm2), we observed similar improvement, which is an inherent outcome of the AS-ALD technique. Our demonstration of AS-ALD for improved RRAM devices could further encourage the adoption of such techniques for other data storage technologies, including phase-change, magnetic, and ferroelectric RAM.

Computational fluid dynamics modeling of a discrete feed atomic layer deposition reactor: Application to reactor design and operation

Novel transistor fabrication methods such as area-selective atomic layer deposition (AS-ALD) are crucial to improving nanopatterning, which is essential for facilitating transistor stacking in semiconducting wafers. However, transistor surfaces are subjected to nonuniformities during the initial AS-ALD adsorption reactions that are attributed to steric hindrance effects. To minimize the role of steric hindrance generated by an oversaturation of reagent on the substrate surface, a discrete feed method is proposed for an ALD reactor configuration where reagent is introduced in short pulses through a perpendicular delivery system. An optimal reactor configuration is developed by modifying the inlet geometries of the reactor to ensure ideal fluid dynamics conditions (e.g., minimal vortices, radial flow distribution) are achieved. Detailed computational fluid dynamics simulations demonstrate the performance of the new reactor configuration and operational strategy.

Intrinsic and atomic layer etching enhanced area-selective atomic layer deposition of molybdenum disulfide thin films

For continual scaling in microelectronics, new processes for precise high volume fabrication are required. Area-selective atomic layer deposition (ASALD) can provide an avenue for self-aligned material patterning and offers an approach to correct edge placement errors commonly found in top-down patterning processes. Two-dimensional transition metal dichalcogenides also offer great potential in scaled microelectronic devices due to their high mobilities and few-atom thickness. In this work, we report ASALD of MoS2 thin films by deposition with MoF6 and H2S precursor reactants. The inherent selectivity of the MoS2 atomic layer deposition (ALD) process is demonstrated by growth on common dielectric materials in contrast to thermal oxide/ nitride substrates. The selective deposition produced few layer MoS2 films on patterned growth regions as measured by Raman spectroscopy and time-of-flight secondary ion mass spectrometry. We additionally demonstrate that the selectivity can be enhanced by implementing atomic layer etching (ALE) steps at regular intervals during MoS2 growth. This area-selective ALD process provides an approach for integrating 2D films into next-generation devices by leveraging the inherent differences in surface chemistries and providing insight into the effectiveness of a supercycle ALD and ALE process.