Area-selective Atomic Layer Deposition Process Research Articles

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.

(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

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.

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.

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.

Multiscale CFD Modeling of Area-Selective Atomic Layer Deposition: Application to Reactor Design and Operating Condition Calculation

Area-selective atomic layer deposition (ASALD) as a bottom-up nanopatterning technique has gained recognition for its ability to address misalignment issues in semiconductor manufacturing. This in silico study investigates process operation conditions for ASALD of SiO2/Al2O3 and reactor optimization by using multiscale computational fluid dynamics (CFD) modeling. Several reactor designs were modeled in Ansys Workbench and their results compared to ensure effective reagent separation and homogeneous exposure to reagents across the wafer. Annular reaction zones and asymmetrical inlets enhanced uniform exposure to reagents and minimized reagent intermixing, which allowed the reactor to tolerate higher rotational speeds. Additionally, low rotation speeds and high species mole fractions were required for complete deposition of a cycle of the ASALD process. This research provides insight into the ASALD process operation and contributes to further industrial versatility.

Area-selective atomic layer deposition of titanium oxide and nitride on vertically aligned carbon nanotubes patterned by Aerosol Jet Printing for 3D Microsupercapacitors

This article demonstrates novel fabrication of the first interdigital 3D microsupercapacitors (MSC) using area-selective atomic layer deposition (ASALD). A unique ASALD process was developed to selectively deposit pseudocapacitive titanium oxide and nitride layers on one or both interdigitated vertically aligned carbon nanotube (VACNT) electrodes to form asymmetric or symmetric 3D MSC devices. This work compliments and expands on our previously published article exploring ALD of thin conformal coatings of TiO2 and TiN on VACNTs for 3D MSCs. Further, we demonstrate the first use of Aerosol Jet Printing, a recently developed additive manufacturing technique, to enable ASALD patterning of 3D MSC devices by direct writing of PMMA inhibitors on and adjacent to relatively thick nanostructured electrodes. The synthesis, characterization, and performance evaluation of ASALD TiN-TiO2-VACNT 3D MSCs described herein provides a novel approach for manufacturing of new nanocomposite based electrochemical energy storage microdevices that could be integrated as an on-chip power source for portable electronics. Results indicated the symmetric ASALD TiN(100)-TiO2(100)-VACNT MSC (6.55 mF cm−2) exhibited nearly two orders of magnitude (94×) improvement in specific capacitance compared to the uncoated VACNT MSC (0.07 mF cm−2), significantly improving energy density (3.28 mWhr cm−2) while maintaining high power density (2.34 mW cm−2).

Atomistic-mesoscopic modeling of area-selective thermal atomic layer deposition

There has been growing interest in area-selective atomic layer deposition (ASALD) with the integration of small-molecule inhibitors (SMIs) to improve the regioselectivity of thin-layer deposition on growth areas. ASALD offers an alternative solution to the challenges for the nanofabrication of transistors: difficulty of achieving self-alignment and imprecise thickness control. In this work, atomistic simulations are performed using density functional theory (DFT) and a mesoscopic model for ASALD is developed on a SiO2/Al2O3 surface based on a kinetic Monte Carlo (kMC) method, which simulates the deposition and reaction processes that take place on the surface. The ASALD process comprises the SMI, acetylacetone, for Step A, precursor, bis(diethylamino)silane (BDEAS), for Step B, and oxidant, ozone, for Step C. The simulation results comprehensively characterize the surface kinetics of ASALD implemented with steric effects that are produced by the SMI and BDEAS and are comparable to the results from experimental findings.

Fluorine-containing polymeric inhibitor for highly selective and durable area-selective atomic layer deposition

Area-selective deposition (ASD) is an emerging technique in the semiconductor industry with a downscaling feature size, as it generally allows a reduction of the number of process steps, improves cost-efficiency and placement accuracy, but remains compatible with CMOS processes. Among various ASD technics, area-selective atomic layer deposition (AS-ALD) with polymeric inhibitors has the advantage of being able to easily manipulate surface chemistry. We propose the AS-ALD of ZnO using a poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA), which shows superior deposition suppression on the surface based on its hydrophobicity. Fluorine is essentially inert to diethyl zinc and H2O, and sufficient thermal stability helps to maximize the nucleation delay of ZnO. We achieved almost perfect selectivity of ZnO AS-ALD between SiO2 and PTFEMA, and the selectivity was highly durable regardless of severe depositing conditions. In addition, the performance was also demonstrated with Cu3N, proving the versatility of the inhibitor for utilizing conventional reactants (H2O and NH3). We fabricated the ZnO field effect transistors as proof-of-concept devices using a polymeric inhibitor and AS-ALD achieving a modest switching property (on/off current ratio > 106). Simple formation and removal of chemical contrast will provide an effective route for employing AS-ALD process to address challenges in recent device fabrication.

Atomic layer deposition and selective etching of ruthenium for area-selective deposition: Temperature dependence and supercycle design

For future sub-5 nm technology nodes, the fabrication of semiconductor devices will likely involve the use of area-selective atomic layer deposition (ALD). While area-selective ALD processes have been reported for a variety of materials, most approaches yield a limited selectivity, for example, due to growth initiation at defects or impurities on the non-growth area. Recently, we demonstrated that Ru ALD can be combined with selective etching to achieve area-selective ALD of metal-on-metal with high selectivity. Cycles consisting of an O2 plasma and an H2 gas dose were integrated in an ALD-etch supercycle recipe to remove unwanted nuclei on the SiO2 non-growth area, while obtaining deposition on the Pt or Ru growth area. The current work discusses the challenging compromise that needs to be made between selectivity and net deposition, considering that the material is also removed from the growth area. After investigating deposition between 100 and 200 °C on SiO2, Al2O3, Pt, and Ru in terms of selectivity and net deposition, a substrate temperature of 150 °C was selected since the difference in Ru thickness on Pt and SiO2/Al2O3 was maximum at this temperature, even though still some deposition occurred on the SiO2 and Al2O3 non-growth areas. Different ALD-etch supercycles were studied, using varying O2 plasma etch times and etch frequencies. The amount of the (undesired) material deposited on the SiO2 non-growth area was quantified, demonstrating that the selectivity improved for longer O2 plasma times. On the basis of the results, a simple mathematical description of the nucleation, growth, and etching effects during ALD-etch supercycles is discussed, which can assist the design of future area-selective deposition processes. Overall, this work illustrates how ALD and etch processes can be tuned to simultaneously obtain a high selectivity and a high net deposition of the material at the desired locations.

Area-selective atomic layer deposition of noble metals: Polymerized fluorocarbon layers as effective growth inhibitors

The increasingly complex nanoscale three-dimensional and multilayered structures utilized in nanoelectronic, catalytic, and energy conversion/storage devices necessitate novel substrate-selective material deposition approaches featuring bottom-up and self-aligned precision processing. Here, we demonstrate the area-selective atomic layer deposition (AS-ALD) of two noble metals, Pt and Pd, by using a plasma-polymerized fluorocarbon layer as growth inhibition surfaces. The contact angle, x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy measurements were performed to investigate the blocking ability of polymerized fluorocarbon (CFx) layers against ALD-grown metal films. Both Pt and Pd showed significant nucleation delays on fluorocarbon surfaces. Self-aligned film deposition is confirmed using this strategy by growing Pt and Pd on the microscale lithographically patterned CFx/Si samples. CFx blocking layer degradation during ozone exposure was analyzed using XPS measurements, which confirmed the oxygen physisorption as the main responsible surface reaction with further hydroxyl group formation on the CFx surface. Our work reveals that the CFx layer is compatible with an ozone coreactant until the blocking polymer cannot withstand oxygen physisorption. Our results could potentially be used to investigate and develop radical-assisted AS-ALD processes for a wider selection of materials.

(Invited) Area-Selective Atomic Layer Deposition of Manganese Oxides on Metal−Dielectric Patterns

Area-selective atomic layer deposition (ALD) is a kind of high-precision deposition technologies where it happens only on designed areas. It is a very promising technology for scaling-down of nanodevices because of the characteristics of sub-nanoscale thickness control and bottom-up self-alignment. In this work, we report inherently selective ALD of MnOx on Pt/SiO2 substrates by adjusting the ALD processes parameters. Mn precursors with different ligands are introduced, namely Mn(thd)3 and Mn(EtCp)2. Through temperature and precursor pulse etc. regulation, an appropriate selective process windows are approached. During the first few ALD cycles, there is a nucleation delay on SiO2 surface, while it grows linearly on metal surface. The results of selectivity may come from the active oxygen on the platinum surface which promoted the reaction, while the dielectric surface has a nucleation delay. Through first-principles calculation, the reaction path and energy barrier are analyzed to explain the selective growth. The study broadens the family of selective deposition and provides guidance for specific applications, such as integrated circuits, optoelectronic devices, etc. Figure 1

Area-Selective Atomic Layer Deposition of TiN Using Aromatic Inhibitor Molecules for Metal/Dielectric Selectivity

Despite the rapid increase in the number of newly developed processes, area-selective atomic layer deposition (ALD) of nitrides is largely unexplored. ALD of nitrides at low temperature is typically achieved by employing a plasma as the coreactant, which is not compatible with most approaches to area-selective ALD. In this work, a plasma-assisted ALD process for area-selective deposition of TiN was developed, which involves dosing of inhibitor molecules at the start of every ALD cycle. Aromatic molecules were identified as suitable inhibitor molecules for metal/dielectric selectivity because of their strong and selective adsorption on transition metal surfaces. A four-step (i.e., ABCD-type) ALD cycle was developed, which comprises aniline inhibitor (step A) and tetrakis(dimethylamino)titanium precursor (step B) dosing steps, followed by an Ar–H2 plasma exposure (step C), during which a substrate bias is applied in the second half of the plasma exposure (step D). This process was demonstrated to allow for ∼6 nm of selective TiN deposition on SiO2 and Al2O3 areas of a nanoscale pattern with Co and Ru non-growth areas. The TiN deposited using this ABCD-type process is of high quality in terms of resistivity (230 ± 30 μΩ cm) and impurity levels. This developed strategy for area-selective ALD of TiN can likely be extended to area-selective ALD of other nitrides.

Area-selective atomic layer deposition of molybdenum oxide

Area-selective bottom-up synthesis routes of thin films are required to overcome the current limits in lithography, and such growth can be achieved with high quality and nanometer thickness control by area-selective atomic layer deposition (AS-ALD). However, the current range of materials demonstrated deposited by AS-ALD is limited, and no processes for molybdenum oxide have been available so far. In this work, the authors explore the properties of a new ALD precursor, MoCl4O, for deposition of molybdenum oxides by ALD. MoCl4O is administered at room temperature during deposition, making it readily available for use. When reacted with a combination of water and ozone, it leads to an AS-ALD process for deposition of MoOx—the first reported. The process is perfectly selective for growth on glass as compared to Si(100) substrates for deposition temperatures between 200 and 300 °C, with a growth rate of 0.72 Å/cycle at 300 °C. The process is attempted on a range of substrates proving good growth on soda-lime glass and LiF and no growth on Si(100), silica, Na2CO3, CaCO3, Li3PO3, or Li2SiO3. The findings of this study indicate an activated process by diffusion of sodium or lithium through the film during growth. The obtained films have further been characterized by x-ray photoelectron spectroscopy, scanning electron microscopy, x-ray diffraction, and atomic force microscopy, revealing films with an RSM roughness of 23 nm with the presence of crystalline MoO2 (C P/m) when deposited at 300 °C and crystalline Mo9O26 when deposited at 250 °C. The rough MoOx thin films may be applicable for electrocatalysis, gas sensors, or lithium-ion batteries. The findings of this study enable AS-ALD synthesis of molybdenum oxide with excellent selectivity not dependent on intermittent etching cycles during growth.

Area-Selective Atomic Layer Deposition of Two-Dimensional WS2 Nanolayers

With downscaling of device dimensions, two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) such as WS2 are being considered as promising materials for future applications in nanoelectronics. However, at these nanoscale regimes, incorporating TMD layers in the device architecture with precise control of critical features is challenging using current top-down processing techniques. In this contribution, we pioneer the combination of two key avenues in atomic-scale processing: area-selective atomic layer deposition (AS-ALD) and growth of 2D materials, and demonstrate bottom-up processing of 2D WS2 nanolayers. Area-selective deposition of WS2 nanolayers is enabled using an ABC-type plasma-enhanced ALD process involving acetylacetone (Hacac) as inhibitor (A), bis(tert-butylimido)-bis(dimethylamido)-tungsten as precursor (B), and H2S plasma as the co-reactant (C) at a low deposition temperature of 250 °C. The developed AS-ALD process results in the immediate growth of WS2 on SiO2 while effectively blocking growth on Al2O3 as confirmed by in situ spectroscopic ellipsometry and ex situ X-ray photoelectron spectroscopy measurements. As a proof of concept, the AS-ALD process is demonstrated on patterned Al2O3/SiO2 surfaces. The AS-ALD WS2 films exhibited sharp Raman (E2g1 and A1g) peaks on SiO2, a fingerprint of crystalline WS2 layers, upon annealing at temperatures within the thermal budget of semiconductor back-end-of-line processing (≤450 °C). Our AS-ALD process also allows selective growth on various TMDs and transition metal oxides while blocking growth on HfO2 and TiO2. It is expected that this work will lay the foundation for area-selective ALD of other 2D materials.

(Invited) Area Selective Atomic Layer Deposition As an Emerging Process for Advanced Nanofabrication

The rapid growth of technologies such as artificial intelligence and autonomous vehicles is fueling a need for more powerful electronic chips, which the semiconductor industry is working to meet with ever-more complex nanoscale device structures. With this growing need for nanostructure fabrication, selective deposition is gaining much attention as an important process to achieve pattern features at the ~10 nm length scale. Both two-dimensional planar geometries and three-dimensional structures will benefit from selective deposition processes, with bottom-up growth strategies providing advantages in reduced process complexity and improved pattern fidelity. In this presentation, we will describe how control over surface chemistry using molecular monolayers can achieve area selective atomic layer deposition (ALD). ALD is a good choice for selective deposition because its chemical specificity provides a means to achieve selectivity on a spatially patterned substrate. In particular, inhibitory layers such as self-assembled monolayers (SAMs) can alter the native surface reactivity, allowing ALD selectivity to be achieved. We will show that this process provides good selectivity for thin deposited films, and demonstrate selective deposition on different materials, including dielectrics and metals such as Cu, Co, W and Ru. Because area selective ALD processes often break down after more than a few nanometers of material is deposited, strategies to overcome the undesired ALD nucleation on the inhibitory layer and achieve significantly higher selectivity in area selective ALD are also important. Two such strategies that improve the final selectivity will be described, including SAM repair between ALD cycles and a self-correcting process in which selective deposition is combined with selective etching. With both approaches, selective ALD of more than 60 nm of metal oxide dielectric material can be achieved. Directions toward new area selective deposition processes will also be described.

Area-Selective Atomic Layer Deposition of ZnO by Area Activation Using Electron Beam-Induced Deposition

Area-selective atomic layer deposition (ALD) of ZnO was achieved on SiO2 seed layer patterns on Hterminated silicon substrates, using diethylzinc (DEZ) as the zinc precursor and H2O as the coreactant. The selectivity of the ALD process was studied using in situ spectroscopic ellipsometry and scanning electron microscopy, revealing improved selectivity for increasing deposition temperatures from 100 to 300 °C. The selectivity was also investigated using transmission electron microscopy and energy-dispersive X-ray spectroscopy. Density functional theory (DFT) calculations were performed to corroborate the experimental results obtained and to provide an atomic-level understanding of the underlying surface chemistry. A kinetically hindered proton transfer reaction from the H-terminated Si was conceived to underpin the selectivity exhibited by the ALD process. By combining the experimental and DFT results, we suggest that the trend in selectivity with temperature may be due to a strong DEZ or H2O physisorption on the H-terminated Si that hampers high selectivity at low deposition temperature. This work highlights the deposition temperature as an extra process parameter to improve the selectivity.

Self-focusing SIMS: A metrology solution to area selective deposition

Micro- and nano-electronics is increasingly relying on heterogeneous, confined and three-dimensional structures, to continue the downscaling required for the next technology generations. Area-selective atomic layer deposition (ALD) is one suited methodology to create nm-scale features through (1) the area-selective self-assembly of a blocking layer (i.e. a thiol deposited on copper) and (2) the ALD growth on the areas not covered with the blocking layer (i.e. a dielectric deposited on low-k). Assessing the efficiency and defectivity of selective deposition on such samples would require a lateral resolution much smaller than the feature size of interest. Hence the need for characterization techniques appropriate to the device’s dimensions. Recently, thanks to the Self-Focusing Secondary Ions Mass Spectrometry (SF-SIMS) concept, the SIMS applicability to analyze the composition of narrow (<20 nm) trenches has been enabled through the selection of characteristic cluster ions exclusively confined to the areas of interest. In this paper, we show that the SF-SIMS concept can be extended to area-selective ALD processes. More specifically, the assessment of the blocking layer deposition on copper is studied using the characteristic copper-sulphur cluster ions while the potential reaction with the low-k material is checked by looking at silicon-sulphur cluster ions. In the same way, the ALD growth of aluminum oxide on the low-k material is assessed using silicon-aluminum clusters while the detection of copper-aluminum clusters is exploited to assess the efficiency of the blocking layer.

From the Bottom-Up: Toward Area-Selective Atomic Layer Deposition with High Selectivity.

Bottom-up nanofabrication by area-selective atomic layer deposition (ALD) is currently gaining momentum in semiconductor processing, because of the increasing need for eliminating the edge placement errors of top-down processing. Moreover, area-selective ALD offers new opportunities in many other areas such as the synthesis of catalysts with atomic-level control. This Perspective provides an overview of the current developments in the field of area-selective ALD, discusses the challenge of achieving a high selectivity, and provides a vision for how area-selective ALD processes can be improved. A general cause for the loss of selectivity during deposition is that the character of surfaces on which no deposition should take place changes when it is exposed to the ALD chemistry. A solution is to implement correction steps during ALD involving for example surface functionalization or selective etching. This leads to the development of advanced ALD cycles by combining conventional two-step ALD cycles with correction steps in multistep cycle and/or supercycle recipes.

Area-Selective Atomic Layer Deposition of Metal Oxides on Noble Metals through Catalytic Oxygen Activation.

Area-selective atomic layer deposition (ALD) is envisioned to play a key role in next-generation semiconductor processing and can also provide new opportunities in the field of catalysis. In this work, we developed an approach for the area-selective deposition of metal oxides on noble metals. Using O2 gas as co-reactant, area-selective ALD has been achieved by relying on the catalytic dissociation of the oxygen molecules on the noble metal surface, while no deposition takes place on inert surfaces that do not dissociate oxygen (i.e., SiO2, Al2O3, Au). The process is demonstrated for selective deposition of iron oxide and nickel oxide on platinum and iridium substrates. Characterization by in situ spectroscopic ellipsometry, transmission electron microscopy, scanning Auger electron spectroscopy, and X-ray photoelectron spectroscopy confirms a very high degree of selectivity, with a constant ALD growth rate on the catalytic metal substrates and no deposition on inert substrates, even after 300 ALD cycles. We demonstrate the area-selective ALD approach on planar and patterned substrates and use it to prepare Pt/Fe2O3 core/shell nanoparticles. Finally, the approach is proposed to be extendable beyond the materials presented here, specifically to other metal oxide ALD processes for which the precursor requires a strong oxidizing agent for growth.