Ru Atomic Layer Deposition Research Articles

The surface chemistry of the atomic layer deposition of ruthenium on aluminum and tantalum oxide surfaces

The surface chemistry of Ru atomic layer deposition (ALD) processes based on the use of tris(2,2,6,6-tetramethyl-3,5-heptanedionato)ruthenium(III) (Ru(tmhd)3) and either molecular oxygen or atomic hydrogen on aluminum oxide films was characterized by a combination of surface-sensitive techniques. The thermal decomposition of the Ru metalorganic precursor was determined, by using a combination of reflection-absorption infrared spectroscopy (RAIRS), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS), to start below 400 K and to take place in a stepwise fashion over a wide range of temperatures. Gas-phase products from this chemistry include 2,2,6,6-tetramethyl-3,5-heptanedione (the protonated ligand, Htmhd; in a TPD peak at 520 K), isobutene (540 K; indicating the fragmentation of the organic ligands), and other products from isomerization and/or aldol condensation (650 and 730 K). This chemistry is accompanied by the reduction of the Ru3+ ions in two stages, involving the loss of some of their ligands and their direct bonding to the substrate first (between 500 and 600 K) and a full reduction to a metallic state later on (600–700 K). ALD cycles using either molecular oxygen or atomic hydrogen resulted in the slow build-up of Ru on the surface, but the co-deposition of carbon could not be avoided, at least in the initial cycles, while the alumina surface was still exposed. With O2, the Ru atoms alternate between partially-oxidized (after the O2 exposures) and zero-valent (after the Ru(tmhd)3 doses) states, and some Ru loss in the form of the volatile RuO4 oxide was seen after the second half of the ALD cycles; neither the Ru oxidation state alternation nor the elimination of some Ru from the surface were observed when using H·. The deposited Ru was determined, by combining results from angle-resolved XPS (ARXPS) and low-energy ion scattering (LEIS) experiments, to grow as 3D nanoparticles rather than as a layer-by-layer 2D film, presumably because the Ru precursor preferentially adsorbs (and decomposes more cleanly) on the metal surface. A discussion is provided of the implications of these results for the design of ALD processes.

(Invited) Internal Photoemission (IPE) Spectroscopy Measurement of Interfacial Energy Barriers in Operating Metal/Insulator/Metal (MIM) and Metal/Ferroelectric/Metal (MFM) Devices

Metal-insulator-metal (MIM) and Metal/Ferroelectric/Metal (MFM) devices find application as high speed tunnel diodes for rectenna based energy harvesting and sensing of IR radiation, hot-electron transistors, single electron transistors, resistive random access memory (RRAM), back end of line (BEOL) capacitors, and ferroelectric tunnel junction (FTJ) diodes. Precise knowledge of band-offsets / energy barriers (φBn) at metal/insulator interfaces is critical for understanding, predicting, and optimizing charge transport in these devices.The Schottky-Mott rule, which neglects charge transfer across interfaces, states that the difference between the Fermi level of a metal (EF) and the conduction band of an insulator should vary simply with the metal vacuum work function (ΦM,vac) and the insulator electron affinity (χi) so that φBn = ΦM,vac - χi. In induced gap state theory, charge transfer at intrinsic interface traps creates an interfacial dipole that drives the EF towards the charge neutral level of the insulator (ECNL,i) the energy at which the dominant character of the interface states switches from donor-like to acceptor-like. A metal on an insulator will thus behave as if it has an effective work function (ΦM-eff) where ΦM,eff = ECNL,I + S(ΦM,vac - ECNL,i), where S = dφBn / dΦM,vac.1 Empirically, S = 1 / (1 + 0.1(εopt - 1)2), so that as the optical dielectric constant of the insulator (εhf) increases, S decreases from an ideal 1 towards 0 so that the insulator more effectively "pins" EFM at ECNL-i.2 Despite some success of MIGS theory, it is difficult to calculate or determine ECNL for a given material and it is observed that actual φBn's often deviate substantially from predictions. Indeed, φBn's depends on material processing, extrinsic effects (such as interfacial and near-interfacial trapped charge arising from point defects), dipoles (due to interfacial chemical reactions), and scavenging of oxygen from the insulator. Therefore, it is necessary to directly measure φBn for the specific metal/insulator or metal/ferroelectric combination in use. Internal photoemission (IPE) spectroscopy is an electro-optical technique that allows measurement of φBn at both metal interfaces in operating MIM & MFM devices.3-5 IPE is the only technique capable of measuring barrier heights, in-situ, in operating device structures. To date, relatively little work has been reported on IPE of these devices.6-12 In this invited talk, IPE spectroscopy measurements are described and measurements are presented of φBn's in MIM structures between insulators (Al2O3, HfO2, SiO2, NiO, CoOx) and ferroelectric HfZrOx deposited via atomic layer deposition (ALD) and various metals including ALD Ru, sputtered thin film amorphous metals (ZrCuAlNi, TaWSi, and TaNiSi), and benchmark metals (TaN, Al, and Au). Comparisons with electrical measurements on the same devices are found to be qualitatively consistent with φBns determined via IPE, even when inconsistent with Schottky model predictions, pointing to various non-idealities present in the materials and their interfaces and demonstrating the power of IPE for understanding and optimizing MIM & MFM device operation. C. Yeo, T.J. King, and C. Hu, J. Appl. Phys. 92, 7266 (2002).Mönch, Phys. Rev. Lett. 58, 1260 (1987).K. Adamchuk and V. V. Afanas’ev, Prog. Surf. Sci. 41, 111 (1992).V. Afanas’ev and A. Stesmans, J. Appl. Phys. 102, 081301 (2007).V. Nguyen, O. A. Kirillov, and J. S. Suehle, Thin Solid Films 519, 2811 (2011).Afanas’ev, N. Kolomiiets, M. Houssa, and A. Stesmans, Phys. Status Solidi A 215, 1700865 (2017).V. Afanas’ev et al., Appl. Phys. Lett. 98, 132901 (2011).A. Jenkins, T. Klarr, D. Z. Austin, W. Li, N. V. Nguyen, and J. F. Conley Jr., Phys. Status Solidi RRL – Rapid Res. Lett. 12, 1700437 (2018).A. Jenkins, J. M. McGlone, J. F. Wager, and J. F. Conley, Jr., J. Appl. Phys. 125, 055301 (2019).A. Jenkins, T. Klarr, J. M. McGlone, J. F. Wager, and J. F. Conley Jr., ECS Trans. 85, 729 (2018).A. Jenkins, K.E.K. Holden, S.W. Smith, M.T. Brumbach, M.D. Henry, C. Weiland, J.C. Woicik, S.T. Jaszewski, J.F. Ihlefeld, and J.F. Conley. ACS AMI 13, 14634 (2021).L. Peterson, T. Mimura, J. Ihlefeld, and J.F. Conley Jr., "Internal Photoemission (IPE) Spectroscopy Measurement of Electrode Energy Barriers in Pristine, Woken, and Poled Ferroelectric HZO MFM Devices," in the American Vacuum Society (AVS) Workshop for Innovative Nano Devices and Systems (WINDS) Book of s, Kona, HI, Dec. 2023.

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

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

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

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

Surface treatment of TaN for sub-2 nm, smooth, and conducting atomic layer deposition Ru films

Atomic layer deposition (ALD) of ruthenium (Ru) is being investigated for next generation interconnects and conducting liners for copper metallization. However, integration of ALD Ru with diffusion barrier refractory metal nitrides, such as tantalum nitride (TaN), continues to be a challenge due to its slow nucleation rates. Here, we demonstrate that an ultraviolet-ozone (UV-O3) pretreatment of TaN leads to an oxidized surface that favorably alters the deposition characteristics of ALD Ru from islandlike to layer-by-layer growth. The film morphology and properties are evaluated via spectroscopic ellipsometry, atomic force microscopy, electrical sheet resistance measurements, and thermoreflectance. We report a 1.83 nm continuous Ru film with a roughness of 0.19 nm and a sheet resistance of 10.8 KΩ/□. The interface chemistry between TaN and Ru is studied by x-ray photoelectron spectroscopy. It is shown that UV-O3 pretreatment, while oxidizing TaN, enhances Ru film nucleation and limits further oxidation of the underlying TaN during ALD. An oxygen “gettering” mechanism by TaN is proposed to explain reduced oxygen content in the Ru film and higher electrical conductivity compared to Ru deposited on native-TaN. This work provides a simple and effective approach using UV-O3 pretreatment for obtaining sub-2 nm, smooth, and conducting Ru films on TaN surfaces.

Growth behavior and mechanism of atomic layer deposition of Ru for replacing Cu-interconnects

The growth behavior and nucleation mechanism of Ru films on various substrates using Ru(EtCp)2 as the precursor and O2 as the reactant were studied systematically. The results show that the Ru films grow rapidly on TiN substrates with almost no incubation time. Different of the segregation and combustion mechanism reported in the previous literature, we established the adsorption and combustion mechanism of ALD-Ru on TiN substrates. SEM and XPS confirmed that the grown Ru films were polycrystalline (average grain size of 16.53 nm, negligible impurities). The Ru films annealed at 600 °C showed significantly low resistivity of 9.73 μΩ•cm, which is one of the lowest resistivities reported in the literature so far. Suppressing electron scattering at grain boundaries is crucial factor to preparing Ru films with low resistivity. The work uses a simple plasma-free technique to construct high-quality Ru films with extremely low resistivity and low impurities, making them one of the ideal candidates for replacing Cu in future ultrafine-pitch interconnects. Furthermore, the work is significant for understanding the growth behaviors and nucleation mechanisms of Ru films on different substrates.

Role of dose optimization in Ru atomic layer deposition for low resistivity films

Ruthenium (Ru) is an alternative to copper (Cu) and cobalt (Co) interconnect layers in sub 20 nm features due to its low resistivity in scaled wires and low diffusion into porous low-K dielectrics (SiCOH). Two goals for a successful Ru atomic layer deposition (ALD) process are to enable films with resistivity values as close as possible to that of bulk Ru and to enable selective deposition to achieve bottom-up fill of vias. In this work, the effects of dose variation on resistivity and selectivity of the Ru ALD process using a dicarbonyl-bis(5-methyl-2, 4-hexanediketonato) Ru(II) precursor, Ru(IHD)2(CO)2 (“Carish”), and O2/He coreactant were investigated. Instead of varying the Carish precursor dose to optimize the growth rate per cycle, the precursor dose was optimized to reduce the film resistivity from 18.5 to 10.2 μΩ cm. By varying the O2/He coreactant dose, the substrate selectivity of the ALD process was successfully enhanced as evidenced by the increased nucleation delay on bis(N,N-dimethylamino)dimethylsilane passivated SiO2 over hydrofluoric acid-cleaned SiO2. These findings highlight the importance of dose optimization beyond the ALD saturation point in developing a selective and low resistivity Ru ALD process. Density functional theory calculations were performed to provide a mechanistic understanding of the underlying surface reactions of the Carish precursor and the roles of CH3 passivation and O2 coreactants.

Area-selective atomic layer deposition of Ru thin films using phosphonic acid self-assembled monolayers for metal/dielectric selectivity

• For potential AS-ALD applications, metal/dielectric selectivity was investigated. • Selective chemisorption of phosphonic acid SAMs was confirmed on TiN and W surfaces. • Blocking capability of SAMs with different ligands was evaluated against Ru ALD. • Ru AS-ALD was successfully demonstrated on metal/dielectric-patterned substrates. We comparatively investigate inhibitory efficacy of four different phosphonic acid (PA) SAMs, octadecylphosphonic acid (ODPA), octylphosphonic acid (OPA), ethylphosphonic acid (EPA), and phenylphosphonic acid (PPA) on TiN and W versus SiO 2 for technologically important metal/dielectric selectivity. Herein, blocking ability of various PA SAM-treated surfaces was evaluated by using Ru atomic layer deposition (ALD) as a representative model process toward metal/dielectric selectivity. Although chemo-selective adsorption features of PA SAMs were obtained on TiN and W relative to SiO 2 , their blocking quality was shown to improve with increasing alkyl chain lengths via strong van der Waals interactions between adjacent SAMs. With the best efficacy of ODPA SAMs, we successfully demonstrated area selective ALD (AS-ALD) of Ru thin films over 15 nm on patterned TiN/SiO 2 surfaces.

Area-selective atomic layer deposition of high-quality Ru thin films by chemo-selective adsorption of short alkylating agents

We report the effects of surface modification by vapor dosing of (N,N-diethylamino)trimethylsilane (DEATMS) molecules as short alkylating agents on technologically important substrates of Si, SiO2, TiN, and W. In this study, tricarbonyl(trimethylenemethane) ruthenium [Ru(TMM)(CO)3] was employed as a metal–organic precursor for atomic layer deposition (ALD) of Ru, which produced high-quality Ru films with significantly low resistivity and high growth-per-cycle. Through surface modification of vapor-dosed DEATMS molecules, significant growth retardation against the ALD Ru process was selectively found on SiO2 and TiN in contrast to Si(-H) and W substrates. With applying chemo-selectively inhibitory characteristics, we successfully demonstrate area selective deposition of ALD Ru films on a patterned TiN/Si substrate.

Oxidation of thermoelectric Bi2Te3-based alloys by atomic layer deposition of Ru metal

Despite the success of heterogeneous coatings of thermoelectric materials by atomic layer deposition (ALD), ALD-grown materials have been limited to oxides with high resistance. In this study, we attempted the nanoinclusion of metals in thermoelectric materials by the deposition of Ru metal on Bi0.4Sb1.6Te3 powders using an ALD with a Ru precursor and O2. As the number of Ru ALD cycles increased, the quantity of deposited Ru increased, and the grain size of Bi0.4Sb1.6Te3 in the sintered Bi0.4Sb1.6Te3 decreased. However, ALD resulted in the oxidation of the Bi0.4Sb1.6Te3 powders because of the high-temperature growth at 300 °C with O2 injection. The thermoelectric properties of the Ru-coated Bi0.4Sb1.6Te3 pellets were governed by oxidation rather than Ru inclusion. This study demonstrates that an oxidation-free ALD process is necessary for the nanoinclusion of Ru in Bi2Te3-based alloys using ALD.

The Importance of Decarbonylation Mechanisms in the Atomic Layer Deposition of High-Quality Ru Films by Zero-Oxidation State Ru(DMBD)(CO)3.

Achieving facile nucleation of noble metal films through atomic layer deposition (ALD) is extremely challenging. To this end, η4 -2,3-dimethylbutadiene ruthenium(0) tricarbonyl (Ru(DMBD)(CO)3 ), a zero-valent complex, has recently been reported to achieve good nucleation by ALD at relatively low temperatures and mild reaction conditions. The authors study the growth mechanism of this precursor by in situ quartz-crystal microbalance and quadrupole mass spectrometry during Ru ALD, complemented by ex situ film characterization and kinetic modeling. These studies reveal that Ru(DMBD)(CO)3 produces high-quality Ru films with excellent nucleation properties. This results in smooth, coalesced films even at low film thicknesses, all important traits for device applications. However, Ru deposition follows a kinetically limited decarbonylation reaction scheme, akin to typical chemical vapor deposition processes, with a strong dependence on both temperature and reaction timescale. The non-self-limiting nature of the kinetically driven mechanism presents both challenges for ALD implementation and opportunities for process tuning. By surveying reports of similar precursors, it is suggested that the findings can be generalized to the broader class of zero-oxidation state carbonyl-based precursors used in thermal ALD, with insight into the design of effective saturation studies.

(Invited) Selective Metal Deposition for Advanced Metallization Schemes

'Invited'Starting from critical dimensions below 10 nm, the continuation of CMOS scaling requires the Cu replacement as an IC interconnect material by a barrierless metal with lower resistivity and better electromigration performance than Cu, such as Co and Ru. In addition, narrow dimensions of interconnect features require implementation of bottom-up metal fill schemes to mitigate defects in metal structures. At the same time, significant technological improvements are required to mitigate the pattern overlays and litho-based edge placement errors when forming multilevel structures with a half-pitch at or below 10 nm. The transition from standard multiple litho-etch deposition schemes to bottom-up area-selective deposition (ASD) is a very promising way to enable self-alignment of multilevel structures. The approaches to achieve ASD can be classified in three categories: i) intrinsic selectivity, ii) selectivity enabled by passivation of the “non-growth area” and iii) selectivity enabled by activation of the “growth area”. Among selective deposition processes, electroless deposition (ELD) and atomic layer deposition (ALD) can be effectively used due to their chemical nature and surface sensitivity. This work explores all three categories of ASD approaches for BEOL technology application, utilizing the above listed techniques for Co and Ru deposition.Intrinsically selective metal deposition can be realized for very limited number of material combinations used in IC manufacturing. Part of this work focuses on various H-based plasma treatments, which allow forming appropriate surface functionalities enabling ASD. Among various material combinations, the focus was set on amorphous carbon (a-C) as “non-growth” surface and Si-based materials, such as SiCN, as “growth” surface. An interaction of various compounds of H-based plasma, namely: H ions and H radicals with a-C was investigated experimentally. In order to support experimental observations, molecular dynamic modeling of a-C interaction with H plasma was performed, which allowed to understand the mechanisms of a-C chemical modification by H ions and radicals. Effectivity of H plasma treatment on ALD selectivity was studied for the case of selective Ru ALD using (ethylbenzyl)(1-ethyl-1,4-cyclohexadienyl)Ru(0) (EBECHRu) precursor with O2 co-reactant. In addition, an initial study of Ru ASD integration into patterned structures of technological relevant dimensions was performed.Direct implementation of intrinsically selective processes into production is a rare case in microelectronic technology. In most of the cases, however, blocking layers can be used. This work explores self-assembled monolayers (SAMs) as blocking layers for ALD. Screening of various siloxane-SAM precursors was performed to study the impact of SAM’s functional group, length of alkyl chain and deposition conditions on surface density of SAM molecules and, specifically, passivation properties of SAM against Ru ALD. An additional study was performed in order to analyze modification of (3-trimethoxysilylpropyl)diethylenetriamine (DETA)-derived SAM under ALD conditions (250 °C and O2 co-reactant). In-situ XPS as well as molecular-dynamic modelling were employed to investigate the mechanisms of DETA modification. Lastly, a removal of DETA-derived SAM from Cu “growth area” selectively with respect to SiO2 “non-growth area” using acetic acid was investigated to mitigate defectivity.Further, surface functionalization by SAMs can also be used to form appropriate surface terminal groups for further attachment of a metal catalyst or metal seed, used in subsequent selective ELD deposition. ELD is based on redox reactions on the metal substrate; therefore, it can be used for intrinsically selective metal deposition on metal substrates or metal seeds. SAMs-enabled selectivity can be used for metal growth on a dielectric surface selectively with respect to another type of the dielectric material. In the case of ELD bottom-up growth in a trench, the metal catalyst should be selectively deposited at the trench bottom dielectric layer. In this work, the selectivity of Pd metal catalyst promoted by selective surface functionalization by SAMs was investigated. It has been shown that SAMs with amino functional groups form covalent bonds with Pd catalyst, which is commonly used as a seed for subsequent ELD of various metals including Co on the Pd seed. Since the electrical properties of interconnect material are of crucial importance, an additional study of ELD Co resistivity was performed, including in-depth analysis of Co recrystallization revealing Co grain size dependency on the film resistivity.In conclusion, area-selective metal deposition processes are an important part of future microelectronic technology. This work explores ASD of Ru and Co, as the most promising Cu replacement metals. For the deposition of these metals, surface sensitive techniques are used, namely ALD and ELD. For the cases, where intrinsic selectively of the deposition technique cannot be realized for the combination of materials used in the process flow, SAM-based passivation and SAM-based activation layers were investigated.

Atomic Layer Deposition of Ru for Replacing Cu-Interconnects

Atomic Layer Deposition of Ru for Replacing Cu-Interconnects

6.2 W/Mm and Record 33.8% PAE at 94 GHz From N-Polar GaN Deep Recess MIS-HEMTs With ALD Ru Gates

This letter reports on the W-band power performance of N-polar GaN deep recess MIS-high electron mobility transistors (HEMTs) using a new atomic layer deposition (ALD) ruthenium (Ru) gate metallization process. The deep recess structure is utilized to control the DC-RF dispersion and increase the conductivity in the access regions. The ALD Ru effectively fills the narrow T-gate stems aiding realization of shorter gate lengths with lower gate resistance than in prior work. In this work, the gate length was scaled down to 48 nm, resulting in the demonstration of a record high 8.1-dB linear transducer gain measured at 94 GHz by load pull. This increased gain has enabled a record 33.8% power-added efficiency (PAE) with an associated output power density ( P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</sub> ) of 6.2 W/mm.

Performance and Stability Enhancement of Ni-Based Cermet Anode Using Atomic Layer Deposited Ruthenium for Direct Methane-Fueled Low-Temperature Solid Oxide Fuel Cell

Nickel (Ni) based cermet, e.g., Ni-doped zirconia(e.g., YSZ) and Ni-doped ceria(e.g., GDC), is the most widely used anode material for solid oxide fuel cell (SOFC). SOFC has been considered as a promising energy converter because of its high efficiency, eco-friendliness, and fuel flexibility. However, recently, SOFC operating below 500°C with more conventional fuels such as hydrocarbon or alcohol are actively studied for overcoming the limitations of high temperature SOFC, e.g., durability, cost, and limited application. Therefore, the necessity of improving the performance and stability of Ni-based anode is aroused because it shows relatively slow hydrocarbon and alcohol oxidation kinetics in the low-temperature regime and vulnerable to carbon deposition. To improve kinetics and stability of Ni-based anode upon hydrocarbon fuel-based operation, various kinds of metal catalysts, e.g., copper, palladium, iron, etc., have been applied using fabrication techniques such as wet synthesis, infiltration, vapor deposition, etc. In this study, ruthenium (Ru) having high catalytic activity and carbon coking toleration is applied to Ni-based cermet anode used in methane-fueled low-temperature SOFC. In particular, atomic layer deposition (ALD), which can deposit nanoparticles conformally on porous structures, is used for depositing Ru nanoparticles on nano-structured Ni-based cermet anode. ALD Ru nanoparticles fabricated in such a way are well-dispersed on the surface of Ni-based cermet anode and effectively improve the performance and stability of the anode when it is operated with methane-fuel. Especially, Ni-based anode with optimal ALD Ru thickness, i.e., 10nm in thickness, shows 40% higher maximum power density than those without ALD Ru overcoating when operated with methane fuel.

Influence of ALD Ru bottom electrode on ferroelectric properties of Hf0.5Zr0.5O2-based capacitors

We report the influence of an ultrathin Ru bottom electrode on ferroelectric properties of fully atomic layer deposition (ALD)-grown Hf0.5Zr0.5O2 (HZO) and La-doped Hf0.5Zr0.5O2 (HZLO)-based ferroelectric capacitors. We show that the Ru bottom electrode deposited by radical enhanced ALD (REALD) improves the remanent polarization of both capacitors considerably. The origin of such a phenomenon is established by grazing-incidence and symmetrical θ–2θ x-ray diffraction measurements. HZO films on Ru exhibit the orthorhombic phase, which is highly (002)-textured in the out-of-plane direction as compared to HZO on TiN. HZLO films demonstrate the rise of (111) intensity of the orthorhombic phase when it is grown on Ru. Both types of capacitors with Ru exhibit a lower wake-up degree as compared to the ones with TiN, which is assumed to be due to the difference in the bottom interface properties. At the same time, both HZO and HZLO on Ru suffer from the relatively early breakdown during electric field cycling, which is presumably due to the high surface roughness of REALD Ru. Taking into account the continuous search for the new precursor's chemicals and ALD processes for Ru, which would be able to provide smother films, ALD Ru might be promising for the hafnium oxide-based ferroelectric random access memory.

Monolithic Integration and Analysis of Vertical, Partially Encapsulated Nanoelectrode Arrays

This study reports on the development of vertical, partially encapsulated nanoelectrodes for electrically contacting the interior of electrogenic cells with microelectronics. Intracellular electrical stimulation and recording with single cell resolution enables new insights into the electrophysiology of cells embedded in a complex multicellular network, providing detailed understanding of fundamental processes affecting cell to cell communication and thereby paving the way for novel applications including pharmacological studies and other neuromodulation techniques like focused ultrasound and electroceuticals. In order to minimize the influence of the measurement system, an approach based on nano-sized hollow electrodes, achieving an adhesion based intracellular access, is used. The focus of the presented work is on the novel fabrication technology and the characterization of the resulting nanoelectrodes. In CMOS compatible processes, the hollow geometry is achieved using a sacrificial layer technique combining deep reactive ion etching and atomic layer deposition of Ru. For decoupling the extracellular milieu, a partial passivation of the nanoelectrodes by Ta2O5 is realized. The monolithic integration allows an application specific fine-tuning of geometry and placement of the nanoelectrodes. A discrete microelectrode array was designed to electrically and electrochemically characterize the nanoelectrodes. Resistance measurements, cyclic voltammetry and electrochemical impedance spectroscopy show the feasibility of the developed electrodes as an electronic interface to electrochemical fluids. Specifically, an electrode resistance of 2.92 $\text{k}\Omega $ and charge delivery capacitance of $748.13~\frac {\mu \text {C}}{\text {cm}^{2}}$ were observed. Confocal microscopy analyses of neural cells interfaced with the nanoelectrodes indicate an adhesion based intracellular access as well as biostability and biocompatibility. [2020-0224]

Selective Atomic Layer Deposition of Metals on Graphene for Transparent Conducting Electrode Application.

Although graphene has considerable potential as a next-generation transparent conducting electrode (TCE) material owing to its excellent optical transparency and flexibility, its electrical properties require further improvement for industrial application. This study reports a pathway of doping graphene by selective atomic layer deposition (ALD) of metals to elevate the electrical conductivity of graphene. Introduction of a novel Pt precursor [dimethyl(N,N-dimethyl-3-butene-1-amine-N)platinum(II); C8H19NPt; DDAP] facilitates a low-temperature (165 °C) process. The sheet resistance (Rs) of graphene is reduced significantly from 471 to 86.8 Ω sq-1 after 200 cycles of Pt ALD, while the optical transmittance at 550 nm (T) is maintained above 90% up to 200 cycles due to the selective growth of Pt on the defects of graphene. Furthermore, comprehensive analysis, including metal (Ru, Pt, and Ni) ALD on graphene, metal (Ru, Pt, Ni, Au, and Co) evaporation on graphene, and change in the ALD chemicals, demonstrates that ALD allows efficient graphene doping and the oxygen affinity of the metal is one of the key properties for efficient graphene doping. Finally, Pt ALD is applied to a multilayer graphene to further reduce Rs down to 75.8 Ω sq-1 yet to be highly transparent (T: 87.3%) after 200 cycles. In summary, the selective ALD of metals opens a way of improving the electrical properties of graphene to a level required for the industrial TCE application and has the potential to promote development of other types of functional metal-graphene composites.

Area-Selective ALD of Ru on Nanometer-Scale Cu Lines through Dimerization of Amino-Functionalized Alkoxy Silane Passivation Films.

The selective deposition of materials on predefined areas on a substrate is of crucial importance for various applications, such as energy harvesting, microelectronic device fabrication, and catalysis. A representative example of area-confined deposition is the selective deposition of a metal film as the interconnect material in multilevel metallization schemes for CMOS technology. This allows the formation of multilevel structures with standard lithographical techniques while minimizing pattern misalignment and overlay and improving the uniformity of the structures across the wafer. In this work, area-selective deposition of Ru by atomic layer deposition (ALD) is investigated using alkoxy siloxane dielectric passivation layers. In this work, a comparison of several silane organic SAM precursors in terms of Ru ALD ASD performance is reported. The importance of the surface areal concentration of the passivation molecules is demonstrated. According to the in situ X-ray photoelectron spectroscopy film characterization, the ALD blocking layers derived from a (3-trimethoxysilylpropyl) diethylenetriamine (DETA) precursor have the ability to polymerize under ALD-compatible temperatures, such as 250 °C, which leads to a significant inhibition of Ru growth up to 400 ALD cycles. At the same time, the DETA layer can be selectively removed from the oxidized Cu surface by rinsing in acetic acid, which allows selective deposition of ca. 14 nm of Ru on Cu with no Ru detected on the DETA-coated surface by RBS. The approach is successfully tested on 50 nm half-pitch patterned SiO2/Cu lines.

Thermal atomic layer deposition of metallic Ru using H2O as a reactant

Abstract Thin Ruthenium (Ru) films were deposited on native SiO2 on Si substrate by thermal atomic layer deposition (ALD) using dicarbonyl-bis(5-methyl-2,4-hexanediketonato)Ru(II) precursor with O2 and H2O as reactant. In the case of the O2 process, increase in the O2 pulse led to oxidation of the film into RuO2. In contrast, purely metallic Ru thin film without significant oxidation was formed using H2O, even with extended H2O pulse. Using H2O, growth rate of ~0.75 A/cycle and electrical resistivity of ~18 μΩcm for metallic Ru were obtained at temperatures as low as 250 °C. Through density functional theory (DFT) calculations, it is shown that adsorption of the Ru precursor would spontaneously occur on metallic Ru surface. Ru ALD using H2O reactant is performed on SiO2 powder to successfully form Ru@SiO2 core-shell structure, demonstrating applicability of this process to substrates with morphological complexity, which often require extended exposures of reactants.