Area-Selective Atomic Layer Deposition of SiO2 Using Acetylacetone as a Chemoselective Inhibitor in an ABC-Type Cycle

Sustained Area-Selectivity in Atomic Layer Deposition of Ir Films: Utilization of Dual Effects of O3 in Deposition and Etching

Area-selective deposition (ASD) based on self-aligned technology has emerged as a promising solution for resolving misalignment issues during ultrafine patterning processes. Despite its potential, the problems of area-selectivity losing beyond a certain thickness remain critical in ASD applications. This study reports a novel approach to sustain the area-selectivity of Ir films as the thickness increases. Ir films are deposited on Al2O3 as the growth area and SiO2 as the non-growth area using atomic-layer-deposition with tricarbonyl-(1,2,3-η)-1,2,3-tri(tert-butyl)-cyclopropenyl-iridium and O3. O3 exhibits a dual effect, facilitating both deposition and etching. In the steady-state growth regime, O3 solely contributes to deposition, whereas in the initial growth stages, longer exposure to O3 etches the initially formed isolated Ir nuclei through the formation of volatile IrO3. Importantly, longer O3 exposure is required for the initial etching on the growth area(Al2O3) compared to the non-growth area(SiO2). By controlling the O3 injection time, the area selectivity is sustained even above a thickness of 25 nm by suppressing nucleation on the non-growth area. These findings shed light on the fundamental mechanisms of ASD using O3 and offer a promising avenue for advancing thin-film technologies. Furthermore, this approach holds promise for extending ASD to other metals susceptible to forming volatile species.

Light-Mediated Contact Printing of Phosphorus Species onto Silicon Using Carbene-Based Molecular Layers

The ability to deposit pattern-specific molecular layers onto silicon with either regional p-/n-doping properties or that act as chemoselective resists for area-selective deposition is highly sought after in the bottom-up manufacturing of microelectronics. In this study, we demonstrate a simple protocol for the covalent attachment and patterning of a phosphorus-based dopant precursor onto silicon(100) functionalized with reactive carbene species. This method relies on selective surface reactions, which provide terminal functionalities that can be photochemically modified via ultraviolet-assisted contact printing between the carbene-functionalized substrate and an elastomeric stamp inked with the inorganic dopant precursor. X-ray photoelectron spectroscopy (XPS) analysis combined with scanning electron microscopy (SEM) imaging was used to characterize the molecule attachment and patterning ability of this technique. XPS spectra are indicative of the covalent bonding between phosphorus-containing molecules and the functionalized surface after both bulk solution-phase reaction and photochemical printing. SEM analysis of the corresponding printed features demonstrates the effective transfer of the phosphorus species in a patterned orientation matching that of the stamp pattern. This simple approach to patterning dopant precursors has the potential to inform the continued refinement of thin-film electronic, photonic, and quantum device manufacturing.

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

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

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

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

Vapor-Phase Halogenation of Hydrogen-Terminated Silicon(100) Using N-Halogen-succinimides

The focus of this study was to demonstrate the vapor-phase halogenation of Si(100) and subsequently evaluate the inhibiting ability of the halogenated surfaces toward atomic layer deposition (ALD) of aluminum oxide (Al2O3). Hydrogen-terminated silicon ⟨100⟩ (H-Si(100)) was halogenated using N-chlorosuccinimide (NCS), N-bromosuccinimide (NBS), and N-iodosuccinimide (NIS) in a vacuum-based chemical process. The composition and physical properties of the prepared monolayers were analyzed by using X-ray photoelectron spectroscopy (XPS) and contact angle (CA) goniometry. These measurements confirmed that all three reagents were more effective in halogenating H-Si(100) over OH-Si(100) in the vapor phase. The stability of the modified surfaces in air was also tested, with the chlorinated surface showing the greatest resistance to monolayer degradation and silicon oxide (SiO2) generation within the first 24 h of exposure to air. XPS and atomic force microscopy (AFM) measurements showed that the succinimide-derived Hal-Si(100) surfaces exhibited blocking ability superior to that of H-Si(100), a commonly used ALD resist. This halogenation method provides a dry chemistry alternative for creating halogen-based ALD resists on Si(100) in near-ambient environments.

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.

Molecular Mechanism of Selective Al2O3 Atomic Layer Deposition on Self-Assembled Monolayers

Area-selective atomic layer deposition (AS-ALD) of insulating metallic oxide layers could be a useful nanopatterning technique for making increasingly complex semiconductor circuits. Although the alkanethiol self-assembled monolayer (SAM) has been considered promising as an ALD inhibitor, the low inhibition efficiency of the SAM during ALD processes makes its wide application difficult. We investigated the deposition mechanism of Al2O3 on alkanethiol-SAMs using temperature-dependent vibrational sum-frequency-generation spectroscopy. We found that the thermally induced formation of gauche defects in the SAMs is the main causative factor deteriorating the inhibition efficiency. Here, we demonstrate that a discontinuously temperature-controlled ALD technique involving self-healing and dissipation of thermally induced stress on the structure of SAM substantially enhances the SAM's inhibition efficiency and enables us to achieve 60 ALD cycles (6.6 nm). We anticipate that the present experimental results on the ALD mechanism on the SAM surface and the proposed ALD method will provide clues to improve the efficiency of AS-ALD, a promising nanoscale patterning and manufacturing technique.

Impact of Surface Hydroxyl Groups on CuO Film Growth by Atomic Layer Deposition

CuO-based nanostructures have been widely investigated in catalysis, sensing, and energy conversion and storage in recent years. The unique properties of these nanostructures are largely related to the morphology and crystallinity of CuO. The controlled deposition of conformal CuO thin films by atomic layer deposition (ALD) has remained challenging until now owing to the limited understanding of the nucleation behavior and growth process. Here, a novel ALD process for copper oxide was developed using copper(II) trifluoroacetylacetonate [Cu(tfacac)2] as the metal precursor. The nucleation and initial growth of a CuO film are strongly dependent on the surface OH concentration. A continuous particulate-like CuO film was grown on OH-abundant pristine SiO2 particles, whereas the surface of the annealed SiO2 particles (presenting mostly isolated OH groups) remained uncoated under the same growth conditions. Moreover, a uniform and conformal CuO film was grown on covalently functionalized CNTs under identical conditions as pristine SiO2 particles. This study provides a strategy for tailoring the structure and the properties of thin films via ALD, which is promising for designing well-tailored nanostructures for various applications.

Self-aligned patterning of tantalum oxide on Cu/SiO2 through redox-coupled inherently selective atomic layer deposition

Atomic-scale precision alignment is a bottleneck in the fabrication of next-generation nanoelectronics. In this study, a redox-coupled inherently selective atomic layer deposition (ALD) is introduced to tackle this challenge. The 'reduction-adsorption-oxidation' ALD cycles are designed by adding an in-situ reduction step, effectively inhibiting nucleation on copper. As a result, tantalum oxide exhibits selective deposition on various oxides, with no observable growth on Cu. Furthermore, the self-aligned TaO_x is successfully deposited on Cu/SiO₂ nanopatterns, avoiding excessive mushroom growth at the edges or the emergence of undesired nucleation defects within the Cu region. The film thickness on SiO₂ exceeds 5 nm with a selectivity of 100%, marking it as one of the highest reported to date. This method offers a streamlined and highly precise self-aligned manufacturing technique, which is advantageous for the future downscaling of integrated circuits.

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

ConspectusAtomically precise and highly selective surface reactions are required for advancing microelectronics fabrication. Advanced atomic processing approaches make use of small molecule inhibitors (SMI) to enable selectivity between growth and nongrowth surfaces. The selectivity between growth and nongrowth substrates is eventually lost for any known combinations, because of defects, new defect formation, and simply because of a Boltzmann distribution of molecular reactivities on surfaces. The selectivity can then be restored by introducing etch-back correction steps. Most recent developments combine the design of highly selective combinations of growth and nongrowth substrates with atomically precise cycles of deposition and etching methods. At that point, a single additional step is often used to passivate the unwanted defects or selected surface chemical sites with SMI. This step is designed to chemically passivate the reactive groups and defects of the nongrowth substrates both before and/or during the deposition of material onto the growth substrate. This approach requires applications of the fundamental knowledge of surface chemistry and reactivity of small molecules to effectively block deposition on nongrowth substrates and to not substantially affect deposition on the growth surface. Thus, many of the concepts of classical surface chemistry that had been developed over several decades can be applied to design such small molecule inhibitors. This article will outline the approaches for such design.This is especially important now, since the ever-increasing number of applications of this concept still rely on trial-and-error approaches in selecting SMI. At the same time, there is a very substantial breadth of surface chemical reactivity analysis that can be put to use in this process that will relate the effectiveness of a potential SMI on any combination of surfaces with the following: selectivity; chemical stability of a molecule on a specific surface; volatility; steric hindrance, geometry, packing, and precursor of choice for material deposition; strength of adsorption as detailed by interdisplacement to determine the most stable SMI; fast attachment reaction kinetics; and minimal number of various binding modes.The down-selection of the SMI from the list of chemicals that satisfy the preliminary criteria will be decided based on optimal combinations of these requirements. Although the specifics of SMI selection are always affected by the complexity of the overall process and will depend drastically on the materials and devices that are or will be needed, this roadmap will assist in choosing the potential effective SMIs based on quite an exhaustive set of "SMI families" in connection with general types of target surfaces.

Inherent area-selective atomic layer deposition of ZnS

Atomic layer deposition processes with inherent substrate selectivity are more straightforward for area-selective atomic layer deposition (AS-ALD) than approaches using surface passivation or activation with self-assembled monolayers (SAMs), small molecule inhibitors (SMIs) or seed layers. Here, ALD of ZnS using elemental zinc and sulfur as precursors is reported to have excellent inherent selectivity. At 400-500 °C for 250 cycles, substantial ZnS growth was observed on Ti and TiO₂ surfaces while no growth was measured on native SiO₂ and Al₂O₃ surfaces. On TiO₂, the ZnS growth rate remains constant at 1.0 Å per cycle at temperatures of 400-500 °C. On Ti, in contrast, the initial growth rate increases significantly from 1.2 Å per cycle at 350 °C to 6.2 Å per cycle at 500 °C. The high growth rates on Ti are believed to be caused by CVD-like growth during the early ALD cycles, arising from the reservoir effect of the Ti layer for Zn atoms. After the first 100 cycles, the growth rate decreases from 3.5 to 1.0 Å per cycle, the same as the growth rate on TiO₂. Selective adsorption of sulfur on TiO₂ over Al₂O₃ and SiO₂ is assumed to be the selectivity mechanism on TiO₂. Self-aligned deposition of ZnS was successfully demonstrated on a micrometer-scale Ti/native SiO₂ pattern and on a nanometer-scale TiO₂/Al₂O₃ pattern at 450 °C for 250 cycles; ZnS films with a thickness of ∼80 nm were selectively deposited on Ti over native SiO₂, and ZnS films with a thickness of ∼23 nm were selectively deposited on TiO₂ over Al₂O₃.

High-Throughput Area-Selective Spatial Atomic Layer Deposition of SiO2 with Interleaved Small Molecule Inhibitors and Integrated Back-Etch Correction for Low Defectivity

A first-of-its-kind area-selective deposition process for SiO₂  is developed consisting of film deposition with interleaved exposures to small molecule inhibitors (SMIs) and back-etch correction steps, within the same spatial atomic layer deposition (ALD) tool. The synergy of these aspects results in selective SiO₂  deposition up to ~23 nm with high selectivity and throughput, with SiO₂  growth area and ZnO nongrowth area. The selectivity is corroborated by both X-ray photoelectron spectroscopy (XPS) and low-energy ion scattering spectroscopy (LEIS). The selectivity conferred by two different SMIs, ethylbutyric acid, and pivalic acid has been compared experimentally and theoretically. Density Functional Theory (DFT) calculations reveal that selective surface functionalization using both SMIs is predominantly controlled thermodynamically, while the better selectivity achieved when using trimethylacetic acid can be explained by its higher packing density compared to ethylbutyric acid. By employing the trimethylacetic acid as SMI on other starting surfaces (Ta₂ O₅ , ZrO₂ , etc.) and probing the selectivity, a broader use of carboxylic acid inhibitors for different substrates is demonstrated. It is believed that the current results highlight the subtleties in SMI properties such as size, geometry, and packing, as well as interleaved back-etch steps, which are key in developing ever more effective strategies for highly selective deposition processes.

Computational Investigation of Precursor Blocking during Area-Selective Atomic Layer Deposition Using Aniline as a Small-Molecule Inhibitor

Area-selective atomic layer deposition using small-molecule inhibitors (SMIs) involves vapor-phase dosing of inhibitor molecules, resulting in an industry-compatible approach. However, the identification of suitable SMIs that yield a high selectivity remains a challenging task. Recently, aniline (C₆H₅NH₂) was shown to be an effective SMI during the area-selective deposition (ASD) of TiN, giving 6 nm of selective growth on SiO₂ in the presence of Ru and Co non-growth areas. In this work, using density functional theory (DFT) and random sequential adsorption (RSA) simulations, we investigated how aniline can effectively block precursor adsorption on specific areas. Our DFT calculations confirmed that aniline selectively adsorbs on Ru and Co non-growth areas, whereas its adsorption on the SiO₂ growth area is limited to physisorption. DFT reveals two stable adsorption configurations of aniline on the metal surfaces. Further calculations on the aniline-functionalized surfaces show that the aniline inhibitor significantly reduces the interaction of Ti precursor, tetrakis(dimethylamino)titanium, with the non-growth area. In addition, RSA simulations showed that the co-presence of two stable adsorption configurations allows for a high surface inhibitor coverage on both Co and Ru surfaces. As the surface saturates, there is a transition from the thermodynamically most favorable adsorption configuration to the sterically most favorable adsorption configuration, which results in a sufficiently dense inhibition layer, such that an incoming precursor molecule cannot fit in between the adsorbed precursor molecules. We also found that, as a result of the catalytic activity of the metallic non-growth area, further reactions of inhibitor molecules, such as hydrogenolysis, can play a role in precursor blocking.

Gradient area-selective deposition for seamless gap-filling in 3D nanostructures through surface chemical reactivity control

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

Padmanabhan S, Davó-Quiñonero A, Darragh P, Senthamaraikannan R, Murphy B, Snelgrove M, McFeely C, Singh S, Conway J, O’Connor R, McGlynn E, Lundy R, Morris MA. Fabrication of High-κ Dielectric Metal Oxide Films on Topographically Patterned Substrates: Polymer Brush-Mediated Depositions

Fabrication of ultrathin films of dielectric (with particular reference to materials with high dielectric constants) materials has significance in many advanced technological applications including hard protective coatings, sensors, and next-generation logic devices. Current state-of-the-art in microelectronics for fabricating these thin films is a combination of atomic layer deposition and photolithography. As feature size decreases and aspect ratios increase, conformality of the films becomes paramount. Here, we show a polymer brush template-assisted deposition of highly conformal, ultrathin (sub 5 nm) high-κ dielectric metal oxide films (hafnium oxide and zirconium oxide) on topographically patterned silicon nitride substrates. This technique, using hydroxyl terminated poly-4-vinyl pyridine (P4VP-OH) as the polymer brush, allows for conformal deposition with uniform thickness along the trenches and sidewalls of the substrate. Metal salts are infiltrated into the grafted monolayer polymer brush films via solution deposition. Tailoring specific polymer interfacial chemistries for ion infiltration combined with subsequent oxygen plasma treatment enabled the fabrication of high-quality sub 5 nm metal oxide films.

Selective Hydration of Rutile TiO2 as a Strategy for Site-Selective Atomic Layer Deposition

The feasibility of a site-selective hydration strategy that enables site-selective atomic layer deposition (ALD) is investigated among four rutile TiO₂ facets [(110), (100), (101) and (001)] and their most prevalent step edges. First-principles simulations of asymmetric slab models were utilized to create accurate representations of pristine terrace and step edge sites. The adsorption free energies for molecular and dissociative adsorption of H₂O were calculated to evaluate this strategy as a viable route to step edge selectivity. We predict that selective hydroxylation is possible on the 110 and 001 step edges and further computationally evaluate three metalorganic ALD precursors for their compatibility with the selective hydration strategy. Experimental evidence for delayed nucleation of ALD on rutile (001), (110), and (100) TiO₂ single crystals corroborates predictions of the dehydration of the surface and suggests the possibility of site-selective ALD.

Relation between Reactive Surface Sites and Precursor Choice for Area-Selective Atomic Layer Deposition Using Small Molecule Inhibitors

Implementation of vapor/phase dosing of small molecule inhibitors (SMIs) in advanced atomic layer deposition (ALD) cycles is currently being considered for bottom-up fabrication by area-selective ALD. When SMIs are used, it can be challenging to completely block precursor adsorption due to the inhibitor size and the relatively short vapor/phase exposures. Two strategies for precursor blocking are explored: (i) physically covering precursor adsorption sites, i.e., steric shielding, and (ii) eliminating precursor adsorption sites from the surface, i.e., chemical passivation. In this work, it is determined whether steric shielding is enough for effective precursor blocking during area-selective ALD or whether chemical passivation is required as well. At the same time, we address why some ALD precursors are more difficult to block than others. To this end, the blocking of the Al precursor molecules trimethylaluminum (TMA), dimethylaluminum isopropoxide (DMAI), and tris(dimethylamino)aluminum (TDMAA) was studied by using acetylacetone (Hacac) as inhibitor. It was found that DMAI and TDMAA are more easily blocked than TMA because they adsorb on the same surface sites as Hacac, while TMA is also reactive with other surface sites. This work shows that chemical passivation plays a crucial role for precursor blocking in concert with steric shielding. Moreover, the reactivity of the precursor with the surface groups on the non-growth area dictates the effectiveness of blocking precursor adsorption.

Functionalization of the SiO2 Surface with Aminosilanes to Enable Area-Selective Atomic Layer Deposition of Al2O3

Small-molecule inhibitors are promising for achieving area-selective atomic layer deposition (ALD) due to their excellent compatibility with industrial processes. In this work, we report on growth inhibition during ALD of Al₂O₃ on a SiO₂ surface functionalized with small-molecule aminosilane inhibitors. The SiO₂ surface was prefunctionalized with bis(dimethylamino)dimethylsilane (BDMADMS) and (N,N-dimethylamino)trimethylsilane (DMATMS) through solution and the vapor phase. ALD of Al₂O₃ using dimethylaluminum isopropoxide (DMAI) and H₂O was performed on these functionalized SiO₂ surfaces. Our in situ four-wavelength ellipsometry measurements show superior growth inhibition when using BDMADMS and DMATMS in sequence over just using BDMADMS or DMATMS. Vapor phase functionalization provided a growth delay of ∼30 ALD cycles, which was similar to solution-based functionalization. Using in situ attenuated total reflection Fourier transform infrared spectroscopy, we show that the interaction of DMAI with SiO₂ surfaces leads to pronounced changes in absorbance for the Si-O-Si phonon mode without any detectable DMAI absorbed on the SiO₂ surface. Detailed analysis of the infrared spectra revealed that the decrease in absorbance was likely caused by the coordination of Al in DMAI to O atoms in surface Si-O-Si bonds without the breaking the Si-O-Si bonds. Finally, we postulate that a minimal amount of DMAI remains adsorbed on surface Si-O-Si bonds even after purging, which can initiate ALD of Al₂O₃ on functionalized SiO₂: this highlights the need for higher surface coverage for enhanced steric blocking.

Conformal and Stoichiometric Chemical Vapor Deposition of Silicon Carbide onto Ultradeep Heterogeneous Micropores by Controlling the Initial Nucleation Stage

Conformal chemical vapor deposition (CVD) of silicon carbide (SiC) from methyltrichlorosilane (MTS) and hydrogen (H2) onto high-aspect-ratio (HAR; typically >100:1) three-dimensional features has been a challenge in the fabrication of ceramic matrix composites. In this study, the impact of heterogeneous underlayers on the initial nucleation of SiC-CVD was studied using HAR (1000:1) microchannels with a tailored wetting underlayer of Si(100) and dewetting underlayers of thermally formed amorphous silicon dioxide (a-SiO2) and turbostratic boron nitride (t-BN). Incubation periods were distributed in the microchannels on a-SiO2 and t-BN underlayers, with the longest period of 70 min found at the feature-bottom due to a decreased concentration (C) of film-forming species. The longer incubation periods with more dewetting underlayers arose due to demoted initial nucleation. Prolonged incubation at the feature bottom led to poor conformality because thick films had already formed at the inlet when film formation began at the feature bottom. The incubation periods were eliminated by increasing the supply of MTS/H2, in accordance with classical heterogeneous nucleation theory. In the meantime, carbon-rich SiC films formed in the vicinity of dewetting a-SiO2 and t-BN underlayers at the feature bottoms, with greater carbon segregation on more dewetting underlayers. This was probably due to the deposition of pyrocarbons (CH4, C2H2, and/or C2H4) generated from MTS/H2 in the gas phase. Decreasing the temperature (T) from 1000 to 900 °C prevented carbon-rich film formation, and the expected deposition rate of pyrocarbon decreased to 0.6% for the case of CH4. A higher C of MTS/H2 combined with a lower T enabled conformal and stoichiometric film formation on the heterogeneous HAR features.

Characterizing Self-Assembled Monolayer Breakdown in Area-Selective Atomic Layer Deposition

To enable area-selective atomic layer deposition (AS-ALD), self-assembled monolayers (SAMs) have been used as the surface inhibitor to block a variety of ALD processes. The integrity of the SAM throughout the ALD process is critical to AS-ALD. Despite the demonstrated effectiveness of inhibition by SAMs, nucleation during ALD eventually occurs on SAM-protected surfaces, but its impact on SAM structures is still not fully understood. In this study, we chose the octadecyltrichlorosilane (ODTS) SAM as a model system to investigate the evolution of crystallinity and structure of SAMs before and after ALD. The breakdown behavior of SAMs when exposed to ZnO and Al₂O₃ ALD was systematically studied by combining synchrotron X-ray techniques and electron microscopy. We show that the crystallinity and structure of ODTS SAMs grown on Si substrates remain intact until a significant amount of material deposition takes place. In addition, the undesired ALD materials that grow on ODTS SAMs present contrasting morphologies: dispersed nanoparticles for ZnO while relatively continuous film for Al₂O₃. Lastly, substrate dependency was explored by comparing a Si substrate to single-crystal sapphire. Similar results in the evolution of SAM crystallinity and formation of ALD nuclei on top of SAM are observed in the ODTS-sapphire system. This study provides an in-depth view of the influence of ALD processes on the SAM structure and the nucleation behavior of ALD on SAM-protected surfaces.

Multimaterial Self-Aligned Nanopatterning by Simultaneous Adjacent Thin Film Deposition and Etching

Printed component sizes in electronic circuits are approaching 10 nm, but inherent variability in feature alignment during photolithography poses a fundamental barrier for continued device scaling. Deposition-based self-aligned patterning is being introduced, but nuclei defects remain an overarching problem. This work introduces low-temperature chemically self-aligned film growth via simultaneous thin film deposition and etching in adjacent regions on a nanopatterned surface. During deposition, nucleation defects are avoided in nongrowth regions because deposition reactants are locally consumed via sacrificial etching. For a range of materials and process conditions, thermodynamic modeling confirms that deposition and etching are both energetically favorable. We demonstrate nanoscale patterning of tungsten at 220 °C with simultaneous etching of TiO₂. Area selective deposition (ASD) of the sacrificial TiO₂ layer produces an orthogonal sequence for self-aligned patterning of two materials on one starting pattern, i.e., TiO₂ ASD on SiO₂ followed by W ASD on Si-H. Experiments also show capacity for self-aligned dielectric patterning via favorable deposition of AlF₃ on Al₂O₃ at 240 °C with simultaneous atomic layer etching of sacrificial ZnO. Simultaneous deposition and etching provides opportunities for low-temperature bottom-up self-aligned patterning for electronic and other nanoscale systems.

Cyclic Plasma Halogenation of Amorphous Carbon for Defect-Free Area-Selective Atomic Layer Deposition of Titanium Oxide

As critical dimensions in integrated circuits continue to shrink, the lithography-based alignment of adjacent patterned layers becomes more challenging. Area-selective atomic layer deposition (ALD) allows circumventing the alignment issue by exploiting the chemical contrast of the exposed surfaces. In this work, we investigate the selective deposition of TiO₂ by plasma halogenation of amorphous carbon (a-C:H) acting as a growth-inhibiting layer. On a-C:H, a CF₄ or Cl₂ plasma forms a thin halogenated layer that suppresses the growth of TiO₂, while nucleation remains unaffected on plasma-treated SiO₂. The same halogenating plasmas preferentially etch TiO₂ nuclei over films and thus enable the restoration of the halogenated surface of amorphous carbon. By embedding the intermediate plasma treatments in the ALD TiO₂ sequence, an 8 nm TiO₂ layer could be deposited with a selectivity of 0.998. The application of the cyclic process on a 60 nm half-pitch line pattern resulted in the defect-free deposition of TiO₂ at the bottom of the trenches. Cyclic fluorination demonstrated better growth inhibition compared to chlorination due to more efficient defect removal and retention of the favorable surface composition during plasma exposure. While exploring the TiO₂ nucleation defects at the limit of detection for conventional elemental analysis techniques (<1 × 10¹⁴ at/cm²), we additionally highlight the value of imaging techniques such as atomic force microscopy for understanding defect formation mechanisms and accurately assessing growth selectivity.

Surface Diffusion Control Enables Tailored-Aspect-Ratio Nanostructures in Area-Selective Atomic Layer Deposition

Area-selective atomic layer deposition is a key technology for modern microelectronics as it eliminates alignment errors inherent to conventional approaches by enabling material deposition only in specific areas. Typically, the selectivity originates from surface modifications of the substrate that allow or block precursor adsorption. The control of the deposition process currently remains a major challenge as the selectivity of the no-growth areas is lost quickly. Here, we show that surface modifications of the substrate strongly manipulate surface diffusion. The selective deposition of TiO₂ on poly(methyl methacrylate) and SiO₂ yields localized nanostructures with tailored aspect ratios. Controlling the surface diffusion allows tuning such nanostructures as it boosts the growth rate at the interface of the growth and no-growth areas. Kinetic Monte-Carlo calculations reveal that species move from high to low diffusion areas. Further, we identify the catalytic activity of TiCl₄ during the formation of carboxylic acid on poly(methyl methacrylate) as the reaction mechanism responsible for the loss of selectivity and show that process optimization leads to higher selectivity. Our work enables the precise control of area-selective atomic layer deposition on the nanoscale and offers new strategies in area-selective deposition processes by exploiting surface diffusion effects.

Selective Gas-Phase Functionalization of SiO2 and SiNx Surfaces with Hydrocarbons

Selective functionalization of dielectric surfaces is required for area-selective atomic layer deposition and etching. We have identified precursors for the selective gas-phase functionalization of plasma-deposited SiO₂ and SiN_x surfaces with hydrocarbons. The corresponding reaction mechanism of the precursor molecules with the two surfaces was studied using in situ surface infrared spectroscopy. We show that at a substrate temperature of 70 °C, cyclic azasilanes preferentially react with an -OH-terminated SiO₂ surface over a -NH_x-terminated SiN_x surface with an attachment selectivity of ∼5.4, which is limited by the partial oxidation of the SiN_x surface. The cyclic azasilane undergoes a ring-opening reaction where the Si-N bond cleaves upon the reaction with surface -OH groups forming a Si-O-Si linkage. After ring opening, the backbone of the grafted hydrocarbon is terminated with a secondary amine, -NHCH₃, which can react with water to form an -OH-terminated surface and release CH₃NH₂ as the product. The surface coverage of the grafted cyclic azasilane is calculated as ∼3.3 × 10¹⁴ cm^-2, assuming that each reacted -OH group contributes to one hydrocarbon linkage. For selective attachment to SiN_x over SiO₂ surfaces, we determined the reaction selectivity of aldehydes. We demonstrate that aldehydes selectively attach to SiN_x over SiO₂ surfaces, and for the specific branched aliphatic aldehyde used in this work, almost no reaction was detected with the SiO₂ surface. A fraction of the aldehyde molecules reacts with surface -NH₂ groups to form an imine (Si-N═C) surface linker with H₂O released as the byproduct. The other fraction of the aldehydes also reacts with surface -NH₂ groups but do not undergo the water-elimination step and remains attached to the surface as an aminoalcohol (Si-NH-COH-). The surface coverage of the grafted aldehyde is calculated as ∼9.8 × 10¹⁴ cm^-2 using a known infrared absorbance cross-section for the -C(CH₃)₃ groups.

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.

Reaction Mechanisms during Atomic Layer Deposition of AlF3 Using Al(CH3)3 and SF6 Plasma

Metal fluorides generally demonstrate a wide band gap and a low refractive index, and they are commonly employed in optics and optoelectronics. Recently, an SF₆ plasma was introduced as a novel co-reactant for the atomic layer deposition (ALD) of metal fluorides. In this work, the reaction mechanisms underlying the ALD of fluorides using a fluorine-containing plasma are investigated, considering aluminum fluoride (AlF₃) ALD from Al(CH₃)₃ and an SF₆ plasma as a model system. Surface infrared spectroscopy studies indicated that Al(CH₃)₃ reacts with the surface in a ligand-exchange reaction by accepting F from the AlF₃ film and forming CH₃ surface groups. It was found that at low deposition temperatures Al(CH₃)₃ also reacts with HF surface species. These HF species are formed during the SF₆ plasma exposure and were detected both at the surface and in the gas phase using infrared spectroscopy and quadrupole mass spectrometry (QMS), respectively. Furthermore, QMS and optical emission spectroscopy (OES) measurements showed that CH₄ and CH _y F_4-y (y ≤ 3) species are the main reaction products during the SF₆ plasma exposure. The CH₄ release is explained by the reaction of CH₃ ligands with HF, while CH _y F_4-y species originate from the interaction of the SF₆ plasma with CH₃ ligands. At high temperatures, a transition from AlF₃ deposition to Al₂O₃ etching was observed using infrared spectroscopy. The obtained insights indicate a reaction pathway where F radicals from the SF₆ plasma eliminate the CH₃ ligands remaining after precursor dosing and where F radicals are simultaneously responsible for the fluorination reaction. The understanding of the reaction mechanisms during AlF₃ growth can help in developing ALD processes for other metal fluorides using a fluorine-containing plasma as the co-reactant as well as atomic layer etching (ALE) processes involving surface fluorination.

Facile rearrangement of molecular layer deposited metalcone thin films by electron beam irradiation for area selective atomic layer deposition

Area selective atomic layer deposition (AS-ALD) is a promising future technology for the realization of a 5 nm scale Si complementary field effect transistor (FET) and its application in industry. AS-ALD is one of the "bottom-up" technologies, which is a key process that can reduce the cost of fabrication and decrease positional error as an alternative to the conventional "top down" technology. We researched an inhibitor for AS-ALD using molecular layer deposited (MLD) films annealed by electron beam irradiation (EBI). We studied the effect of EBI on an indicone film that was fabricated by using bis(trimethylsilyl)amidodiethyl indium (INCA-1), hydroquinone (HQ), an alucone film fabricated by using trimethylaluminum (TMA) and 4-mercaptophenol (4MP). The EBI effect on MLD films was evaluated by investigating the changes in thickness, composition and structure. In order to observe the selectivity of the annealed indicone film, atomic layer deposition of ZnO was performed on the annealed indicone/silicon line pattern, and it was found that the surface of annealed indicone can inhibit ALD of ZnO for 20 cycles as compared to a Si surface.

Precise Definition of a "Monolayer Point" in Polymer Brush Films for Fabricating Highly Coherent TiO2 Thin Films by Vapor-Phase Infiltration

In this work, we show that in order to fabricate coherent titania (TiO₂) films with precise thickness control, it is critical to generate a complete polymer brush monolayer. To date, demonstrations of such dense polymer monolayer formation that can be utilized for inorganic infiltration have been elusive. We describe a versatile bottom-up approach to covalently and rapidly (60 s processing) graft hydroxyl-terminated poly(2-vinyl pyridine) (P2VP-OH) polymers on silicon substrates. P2VP-OH monolayer films of varying thicknesses can subsequently be used to fabricate high-quality TiO₂ films. Our innovative strategy is based upon room-temperature titanium vapor-phase infiltration of the grafted P2VP-OH polymer brushes that can produce TiO₂ nanofilms of 2-4 nm thicknesses. Crucial parameters are explored, including molecular weight and solution concentration for grafting dense P2VP-OH monolayers from the liquid phase with high coverage and uniformity across wafer-scale areas (>2 cm²). Additionally, we compare the P2VP-OH polymer systems with another reactive polymer, poly(methyl methacrylate)-OH, and a relatively nonreactive polymer, poly(styrene)-OH. Furthermore, we prove the latter to be effective for surface blocking and deactivation. We show a simple process to graft monolayers for polymers that are weakly interacting with one another but more challenging for reactive systems. Our methodology provides new insight into the rapid grafting of polymer brushes and their ability to form TiO₂ films. We believe that the results described herein are important for further expanding the use of reactive and unreactive polymers for fields including area-selective deposition, solar cell absorber layers, and antimicrobial surface coatings.

Effect of Multilayer versus Monolayer Dodecanethiol on Selectivity and Pattern Integrity in Area-Selective Atomic Layer Deposition

Monolayer and multilayer dodecanethiols (DDT) can be assembled onto a copper surface from the vapor phase depending on the initial oxidation state of the copper. The ability of the copper-bound dodecanethiolates to block atomic layer deposition (ALD) and the resulting behavior at the interfaces of Cu/SiO₂ patterns during area-selective ALD (AS-ALD) are compared between mono- and multilayers. We show that multilayer DDT is ∼7 times more effective at blocking ZnO ALD from diethylzinc and water than is monolayer DDT. Conversely, monolayer DDT exhibits better performance than does multilayer DDT in blocking of Al₂O₃ ALD from trimethylaluminum and water. Investigation into interfacial effects at the interface between Cu and SiO₂ on Cu/SiO₂ patterns reveals both a gap at the SiO₂ edges and a pitch size-dependent nucleation delay of ZnO ALD on SiO₂ regions of multilayer DDT-coated patterns. In contrast, no impact on ZnO ALD is observed on the SiO₂ regions of monolayer DDT-coated patterns. We also show that these interfacial effects depend on the ALD chemistry. Whereas an Al₂O₃ film grows on the TaN diffusion barrier of a DDT-treated Cu/SiO₂ pattern, the ZnO film does not. These results indicate that the structure of the DDT layer and the ALD precursor chemistry both play an important role in achieving AS-ALD.

Designing Nanoparticles and Nanoalloys for Gas-Phase Catalysis with Controlled Surface Reactivity Using Colloidal Synthesis and Atomic Layer Deposition

Supported nanoparticles are commonly applied in heterogeneous catalysis. The catalytic performance of these solid catalysts is, for a given support, dependent on the nanoparticle size, shape, and composition, thus necessitating synthesis techniques that allow for preparing these materials with fine control over those properties. Such control can be exploited to deconvolute their effects on the catalyst's performance, which is the basis for knowledge-driven catalyst design. In this regard, bottom-up synthesis procedures based on colloidal chemistry or atomic layer deposition (ALD) have proven successful in achieving the desired level of control for a variety of fundamental studies. This review aims to give an account of recent progress made in the two aforementioned synthesis techniques for the application of controlled catalytic materials in gas-phase catalysis. For each technique, the focus goes to mono- and bimetallic materials, as well as to recent efforts in enhancing their performance by embedding colloidal templates in porous oxide phases or by the deposition of oxide overlayers via ALD. As a recent extension to the latter, the concept of area-selective ALD for advanced atomic-scale catalyst design is discussed.

Molecular-Scale Investigation of the Thermal and Chemical Stability of Monolayer PTCDA on Cu(111) and Cu(110)

Perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) has been intensively investigated for decades because of its unique electronic and optical properties and its applications in organic electronics and surface engineering and passivation of 2D materials. Recently, the high demand for achieving selective area deposition in device fabrications drives the research of utilizing organic molecules as a passivation layer on metals in the semiconductor industry. PTCDA molecules show promising potential to be used as a passivation layer on a metal surface because of their ability to form self-assembled compact lying-down layers with the well-exposed inert conjugated molecular π-plane. However, the thermal and chemical stabilities of monolayer PTCDA on metal surfaces have not been thoroughly studied. In this paper, we demonstrate that monolayer PTCDA on Cu(110) and Cu(111) surfaces exhibit good thermal and chemical stabilities, as revealed through the combination of in situ X-ray photoelectron spectroscopy and in situ low-temperature scanning tunneling microscopy measurements. We show that monolayer PTCDA on copper is stable up to 220 °C and decomposes to perylene at higher temperature. Monolayer PTCDA also shows good chemical stability when exposed to O₂ and water, demonstrating good potential for its future applications as passivation layers in selective area deposition.

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 (E _2g ¹ and A _1g) 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.

Competitive Adsorption as a Route to Area-Selective Deposition

In this work, we have explored the use of a third species during chemical vapor deposition (CVD) to direct thin-film growth to occur exclusively on one surface in the presence of another. Using a combination of density functional theory (DFT) calculations and experiments, including in situ surface analysis, we have examined the use of 4-octyne as a coadsorbate in the CVD of ZrO₂ thin films on SiO₂ and Cu surfaces. At sufficiently high partial pressures of the coadsorbate and sufficiently low substrate temperatures, we find that 4-octyne can effectively compete for adsorption sites, blocking chemisorption of the thin-film precursor, Zr[N(CH₃C₂H₅)]₄, and preventing growth on Cu, while leaving growth unimpeded on SiO₂. The selective dielectric-on-dielectric (DoD) process developed herein is fast, totally vapor phase, and does not negatively alter the composition or morphology of the deposited thin film. We argue that this approach to area-selective deposition (ASD) should be widely applicable, provided that suitable candidates for preferential binding can be identified.

Understanding chemical and physical mechanisms in atomic layer deposition

Atomic layer deposition (ALD) is a powerful tool for achieving atomic level control in the deposition of thin films. However, several physical and chemical phenomena can occur which cause deviation from "ideal" film growth during ALD. Understanding the underlying mechanisms that cause these deviations is important to achieving even better control over the growth of the deposited material. Herein, we review several precursor chemisorption mechanisms and the effect of chemisorption on ALD growth. We then follow with a discussion on diffusion and its impact on film growth during ALD. Together, these two fundamental processes of chemisorption and diffusion underlie the majority of mechanisms which contribute to material growth during a given ALD process, and the recognition of their role allows for more rational design of ALD parameters.

Spontaneous selective deposition of iron oxide nanoparticles on graphite as model catalysts

Iron oxide nanomaterials participate in redox processes that give them ideal properties for their use as earth-abundant catalysts. Fabricating nanocatalysts for such applications requires detailed knowledge of the deposition and growth. We report the spontaneous deposition of iron oxide nanoparticles on HOPG in defect areas and on step edges from a metal precursor solution. To study the nucleation and growth of iron oxide nanoparticles, tailored defects were created on the surface of HOPG using various ion sources that serve as the target sites for iron oxide nucleation. After solution deposition and annealing, the iron oxide nanoparticles were found to nucleate and coalesce at 400 °C. AFM revealed that the particles on the sp³ carbon sites enabled the nanoparticles to aggregate into larger particles. The iron oxide nanoparticles were characterized as having an Fe³⁺ oxidation state and two different oxygen species, Fe-O and Fe-OH/Fe-OOH, as determined by XPS. STEM imaging and EDS mapping confirmed that the majority of the nanoparticles grown were converted to hematite after annealing at 400 °C. A mechanism of spontaneous and selective deposition on the HOPG surface and transformation of the iron oxide nanoparticles is proposed. These results suggest a simple method for growing nanoparticles as a model catalyst.

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.

Isotropic Atomic Layer Etching of ZnO Using Acetylacetone and O2 Plasma

Atomic layer etching (ALE) provides Ångström-level control over material removal and holds potential for addressing the challenges in nanomanufacturing faced by conventional etching techniques. Recent research has led to the development of two main classes of ALE: ion-driven plasma processes yielding anisotropic (or directional) etch profiles and thermally driven processes for isotropic material removal. In this work, we extend the possibilities to obtain isotropic etching by introducing a plasma-based ALE process for ZnO which is radical-driven and utilizes acetylacetone (Hacac) and O₂ plasma as reactants. In situ spectroscopic ellipsometry measurements indicate self-limiting half-reactions with etch rates ranging from 0.5 to 1.3 Å/cycle at temperatures between 100 and 250 °C. The ALE process was demonstrated on planar and three-dimensional substrates consisting of a regular array of semiconductor nanowires (NWs) conformally covered using atomic layer deposition of ZnO. Transmission electron microscopy studies conducted on the ZnO-covered NWs before and after ALE proved the isotropic nature and the damage-free characteristics of the process. In situ infrared spectroscopy measurements were used to elucidate the self-limiting nature of the ALE half-reactions and the reaction mechanism. During the Hacac etching reaction that is assumed to produce Zn(acac)₂, carbonaceous species adsorbed on the ZnO surface are suggested as the cause of the self-limiting behavior. The subsequent O₂ plasma step resets the surface for the next ALE cycle. High etch selectivities (∼80:1) over SiO₂ and HfO₂ were demonstrated. Preliminary results indicate that the etching process can be extended to other oxides such as Al₂O₃.

Fifteen Nanometer Resolved Patterns in Selective Area Atomic Layer Deposition-Defectivity Reduction by Monolayer Design

Selective area atomic layer deposition (SA-ALD) offers the potential to replace a lithography step and provide a significant advantage to mitigate pattern errors and relax design rules in semiconductor fabrication. One class of materials that shows promise to enable this selective deposition process are self-assembled monolayers (SAMs). In an effort to more completely understand the ability of these materials to function as barriers for ALD processes and their failure mechanism, a series of SAM derivatives were synthesized and their structure-property relationship explored. These materials incorporate different side group functionalities and were evaluated in the deposition of a sacrificial etch mask. Monolayers with weak supramolecular interactions between components (for example, van der Waals) were found to direct a selective deposition, though they exhibit significant defectivity at and below 100 nm feature sizes. The incorporation of stronger noncovalent supramolecular interacting groups in the monolayer design, such as hydrogen bonding units or pi-pi interactions, did not produce an added benefit over the weaker interacting components. Incorporation of reactive moieties in the monolayer component that enabled the polymerization of an SAM surface, however, provided a more effective barrier, greatly reducing the number and types of defects observed in the selectively deposited ALD film. These reactive monolayers enabled the selective deposition of a film with critical dimensions as low as 15 nm. It was also found that the selectively deposited film functioned as an effective barrier for isotropic etch chemistries, allowing the selective removal of a metal without affecting the surrounding surface. This work enables selective area ALD as a technology through (1) the development of a material that dramatically reduces defectivity and (2) the demonstrated use of the selectively deposited film as an etch mask and its subsequent removal under mild conditions.

Vapor-Phase Cleaning and Corrosion Inhibition of Copper Films by Ethanol and Heterocyclic Amines

Cleaning and passivation of metal surfaces are necessary steps for selective film deposition processes that are attractive for some microelectronic applications (e.g., fully aligned vias or self-aligned contacts). For copper, there is limited knowledge about the mechanisms of the copper oxide reduction process and subsequent passivation layer formation reactions. We have investigated the in situ cleaning (i.e., oxidation and reduction by vapor-phase species) and passivation of chemical-mechanical polishing (CMP)-prepared Cu films in an effort to derive the mechanisms associated with selectively tailoring the surface chemistry. By monitoring the interaction of vapor-phase ethanol with the surface species generated after ozone cleaning at 300 °C, we find that the optimum procedure to remove these species and avoid byproduct redeposition is to use atomic layer deposition (ALD)-like binary cycles of ethanol and N₂, with active pumping. We have further explored passivation of clean Cu using benzotriazole and 2,2'-bipyridine in an ALD environment. Both molecules chemisorb on clean Cu in an upright orientation, with respect to the metal surface at temperatures higher than the melting point of the organic inhibitors (100 ≤ T < 300 °C). Both molecules desorb without decomposition from clean Cu above 300 °C but not from Cu₂O. Previous studies related to the passivation of Cu surfaces using heterocyclic amines have focused on solution-based or ultrahigh vacuum applications of the passivation molecules onto single crystalline Cu samples. The present work explores more industrially relevant vapor-phase passivation of CMP-cleaned, electroplated Cu samples using ALD-like processing conditions and in situ vapor-phase cleaning.

Local Structure and Point-Defect-Dependent Area-Selective Atomic Layer Deposition Approach for Facile Synthesis of p-Cu2O/n-ZnO Segmented Nanojunctions

Area-selective atomic layer deposition (AS-ALD) has attracted much attention in recent years due to the possibility of achieving accurate patterns in nanoscale features, which render this technique compatible with the continuous downscaling in nanoelectronic devices. The growth selectivity is achieved by starting from different materials and results (ideally) in localized growth of a single material. We propose here a new concept, more subtle and general, in which a property of the substrate is modulated to achieve localized growth of different materials. This concept is demonstrated by selective growth of high-quality metallic Cu and semiconducting Cu₂O thin films, achieved by changing the type of majority point defects in the ZnO underneath film exposed to the reactive species using a patterned bilayer structure composed of highly conductive and highly resistive areas, as confirmed by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The selective growth of these materials in a patterned ZnO/Al-doped ZnO substrate allows the fabrication of p-Cu₂O/n-ZnO nanojunctions showing a nonlinear rectifying behavior typical of a p-n junction, as confirmed by conductive atomic force microscopy (C-AFM). This process expands the spectra of materials that can be grown in a selective manner by ALD and opens up the possibility of fabricating different architectures, taking advantage of the area-selective deposition. This offers a variety of opportunities in the field of transparent electronics, catalysis, and photovoltaics.

Catalyzed Atomic Layer Deposition of Silicon Oxide at Ultralow Temperature Using Alkylamine

We report the catalyzed atomic layer deposition (ALD) of silicon oxide using Si₂Cl₆, H₂O, and various alkylamines. The density functional theory (DFT) calculations using the periodic slab model of the SiO₂ surface were performed for the selection of alternative Lewis base catalysts with high catalytic activities. During the first half-reaction, the catalysts with less steric hindrance such as pyridine would be more effective than bulky alkylamines despite lower nucleophilicity. On the other hand, during the second half-reaction, the catalysts with a high nucleophilicity such as triethylamine (Et₃N) would be more efficient because the steric hindrance is less critical. The in situ process monitoring shows that the calculated atomic charge is a good indicator for expecting the catalyst activity in the ALD reaction. The use of Et₃N in the second half-reaction was essential to improving the growth rate as well as the step coverage of the film because the Et₃N-catalyzed process deposited a SiO₂ film with a step coverage of 98% that is better than 93% of the pyridine-catalyzed process. The adsorption of pyridine, ammonia (NH₃), or trimethylamine (Me₃N) salts was more favorable than that of Et₃N, n-Pr₃N, or ⁱPr₃N salts. Therefore, Et₃N was expected to incorporate less amine salts in the film as compared to pyridine, and the compositional analyses confirmed that the concentrations of Cl and N by the Et₃N-catalyzed process were significantly lower than those by the pyridine-catalyzed process.