Step Coverage Research Articles

Formation of highly conformal spinel lithium titanate thin films based on a novel three-step atomic layer deposition process

Lithium titanate (Li4Ti5O12) (LTO) has several promising properties with regard to energy storage. The most important is its low volume expansion during lithium (de-) intercalation enabling the material for complex three-dimensional battery anode designs. To employ this property at a small scale, e.g., for micro batteries (<100 nm active layer thickness), a highly conformal deposition process like atomic layer deposition (ALD) is needed. However, the ALD of lithium containing layers is quite ambitious. Particularly, thermally activated deposition of lithium containing layers with water as a coreactant is challenging due to the high reactivity and hygroscopic nature of many lithium compounds, e.g., lithium hydroxide. That is why a novel ALD process regime has been developed, which allows the deposition of highly conformal and single phase LTO layers with excellent step coverage and composition. The process uses two metalorganic precursors: one acting as lithium and another as a titanium source. In contrast to usual ALD processes, these two precursors are subsequently applied. The reactive pulse with water is applied after the two metal precursor pulses. In this work, this novel ALD process sequence has been introduced and successfully demonstrated on 200 mm wafers using standard industrial ALD equipment. The layers are transformed to single phase Li4Ti5O12 by rapid thermal processing as proven by crystal phase analysis. Elemental composition has been analyzed by time of flight secondary ion mass spectrometry and x-ray photoelectron spectroscopy (XPS). Results show that the amounts of contaminants like carbon and chlorine are below the detection limits of XPS. Also, a uniform element distribution and stoichiometry in good agreement with theoretical expectations for lithium titanate could be shown.

Evaluation of grating realized via pulse current electroplating combined with atomic layer deposition as an x-ray grating interferometer

In this work, the authors developed a simple and efficient two-step deposition process for the realization of an x-ray absorption grating: ALD (atomic layer deposition) of a conductive seed layer, followed by electroplating of the absorbing metal with a pulse current mode. An Si grating with a high aspect ratio of 1:40 was fabricated by deep reactive ion etching on an 8 in. Si wafer. In order to form a conductive seed layer on the Si grating with such a high aspect ratio over an area of 10 × 10 cm2, Ru was conformally deposited by a thermal ALD process with O2 reactant gas. The authors analyzed the results of electroplating performed in different bias modes to fill Au in a high aspect ratio Si grating structure. It was found that electroplating in the pulse current mode (duty cycle: 5%, current density: 1.7 mA/cm2) for 79 h allowed Au to uniformly fill the entire grating area, whereas in the direct current mode, severe step coverage on top of the grating was observed. The authors successfully tested the grating fabricated by the suggested two-step deposition process as an absorption grating (G2) for a high x-ray energy Talbot-Lau grating interferometer.

(Invited) Implementation of Three-Dimensional Solid State Battery

While increasing the multifunction of wearable devices such as smart watch, earphone, and glasses, the run-time of battery is getting more important to be a competitive product in the wearable market. In order to get more reliable and longer lasting battery, the concepts of 3D battery architecture have been suggested to improve energy density [1]. Several 3D microbattery architectures have been proposed to maximize the areal energy density and rate discharge capability by maintaining short ion-transport distances between cathode and anode [2]. However, the implementation of high areal capacity 3D electrode is difficult to fabricate due to the limitation of manufacturing processing [3]. Moreover, conventional fabrication technology of the thin film electrolyte cannot make good step coverage of the 3D conformal electrolyte. In this research, we propose technical approaches to fabricate a high energy density 3D battery structure with good step coverage of the 3D conformal electrolyte. First, we developed a high aspect ratio (=h/w, where h is height and w is width of cathode) 3D cathode which consists of only LiCoO2 with high electrode density without any binder and conductive additives. And then, two kinds of different solid electrolyte layers, LLZO and LiPON, were applied to the 3D conformal coating on the 3D cathode by sol-gel and CVD processing. The process of sol gel and CVD efficiently improved step coverage of 3D conformal electrolyte. Subsequently, Li-metal was evaporated to make a bed for striping and plating as anode. Finally, the 3D solid state battery was evaluated and analyzed for the feasibility study of a next generation battery.

Low temperature chemical vapor deposition of superconducting molybdenum carbonitride thin films

Thin films of molybdenum carbonitride, MoCxNy, are deposited by low temperature chemical vapor deposition from Mo(CO)6 and NH3 in the temperature range 150–300 °C. At a substrate temperature of 200 °C and Mo(CO)6 pressure of 0.01 mTorr, the composition varies from MoC0.48N0.20 to MoC0.36N0.33 (i.e., greater nitrogen and less carbon content) upon increasing the ammonia pressure from 0.3 to 3.3 mTorr. At a constant Mo(CO)6 pressure of 0.01 mTorr and an NH3 pressure of 2 mTorr, the composition varies from MoC0.50N0.30 to MoC0.12N0.40 with increasing substrate temperature from 150 to 300 °C. Selected films grown at substrate temperatures of 150, 200, and 250 °C are superconducting with critical temperatures of 4.7, 4.5, and 5.2 K, respectively. Grazing incidence x-ray diffraction data indicate that the films are crystalline and isomorphous with the cubic phases of Mo2N and Mo2C. With a forward-directed flux of precursors toward the surface, film growth is highly conformal in microtrenches of aspect ratio 6, with step coverages of ∼0.85 and 0.80 at growth temperatures of 150 and 200 °C, respectively.

Influence of Polysilicon Deposition Conditions on Advanced 3D NAND

As the conductive channel, undoped channel hole polysilicon (poly-Si) plays a significant role in 3D NAND. Two important properties i.e. grain size and step coverage (S/C) of undoped channel hole poly-Si have attracted great attentions in practical manufacturing. The grain size affects the mobility of conductive poly-Si film and large grain size usually leads to high mobility. The step coverage influences the subthreshold swing (SS) and improved step coverage leads to small SS. In this paper, during the growth of poly-Si, the influence of different deposition conditions, such as temperature and gas source ratio between Si2H6 and SiH4, on the grain size and step coverage is investigated comprehensively. Grain size and step coverage are characterized using by Transmission Electron Microscope (TEM) and Precession Electron Diffraction (PED). It is found that as the decrease of deposition temperature, both the grain size and step coverage are improved. Compared to gas source SiH4, the employment of Si2H6 is beneficial in achieving large grain size to some degree and no further improvement can be obtained when the flow of Si2H6 is increased to a certain value. However, as-deposited poly-Si exhibits poorer step coverage using Si2H6 in contrast to SiH4.

Advanced barrier and seed layer deposition enabling multiple type of TSVs integration

TSV integration is a key technology allowing heterogeneous devices 3D integration. However, depending on the targeted application, various TSV sizes and integration schemes exist, all requesting very high aspect ratio. The most common integration is the Mid-process TSV for which aspect ratio is required to be higher than 10:1 whatever application. In the case of large interposers, silicon thickness has to be increased to limit the deformation of the substrate due to highly stressed devices. Same requirements are made by photonic interposers which use thick SOI substrate leading to high warpage during integration. In the opposite, imagers requires to save silicon surface thus reduce TSV size and keep out zone. Silicon thickness has to be kept in the 100 μm range leading then the aspect ratio of the TSV to increase. Recently, Hybrid bonding progresses allowed a new type of TSV to be introduced : High Density TSVs for imagers. In this application, micrometer range TSV have to be filled with a Silicon thickness reduction limited to 10 μm by grinding process control. In order to allow the metal filling of all those type of structures, we have developed a highly conformal barrier and seed layer processes using standard materials for easier integration. The process is based on the use of MOCVD TiN as a barrier. This material is deposited using TDMAT precursor which allows low temperature deposition (200 °C)[1] which extends also the polyvalence of the process toward polymer bonded integrations. The very high step coverage of this process, reported at more than 30% in 20:1 aspect ratio coupled to high resistance to copper diffusion allows as thin as 20 nm barrier thickness which appears relevant economically (for deposition and CMP) and for stress consideration, compared to the well known but thicker PVD TaN process. Considering seed layer, the eG3D process[2] was brought to a high maturity allowing it to be integrated in an applied material raider tool coupled to TSV filling reactors. This process, based on electrografting of copper has already proved a step coverage of more than 50% in 12:1 aspect ratio structures. The presented work shows that the same process requires only deposition parameters change to be able to fully cover 10×150 μm Mid-process TSV as well as 1×10 μm High density ones. The excellent step coverage of this process allowed as thin as 200 nm (for 10×120 μm TSVs) and 100 nm (for (1×10 μm ones) deposited thicknesses to ensure perfect coverage of the structures. eG3D process also has the ability to be used as a repair process for non-continuous widely used PVD Cu seed layers but also be deposited directly on the barrier material. These 2 layers were evaluated together in a 300mm TSV integration schemes of both 10×120 mid process and 1×10 μm High Density structures and qualified electrically. The paper will discuss the deposition process development leading to simultaneously allow copper filling of the very wide range of TSVs on the same process equipment and using the same chemicals. We will then present integration results as well as electrical test of TSV daisy chains of both mid and High density TSVs showing excellent yield for all TSV size and integration schemes.

Electroless Grafting of Polymer Insulation Layers in Through-Silicon Vias

A through-silicon via (TSV) with a polymeric insulation layer is promising in three-dimensional packaging technology because of its outstanding electrical properties. In this study, we present an electroless grafting method to realize the fabrication of a thin insulation layer in high aspect ratio TSVs. The proposed method is based on the polymerization of a vinyl monomer and an aryl diazonium salt on a silicon surface. Both poly(acrylic acid) and poly(methyl methacrylate) insulation layers were successfully prepared in TSVs to demonstrate the feasibility of the proposed method to fabricate hydrophilic and hydrophobic layers. The resulting polymer insulation layer exhibited high step coverage and superior dielectric properties. The electroless grafting method is a novel synthesis route to prepare polymeric insulation layers with outstanding dielectric properties in high aspect ratio TSVs.

High chemical resistance and Raman enhancement in Ag/Al2O3 core-shell plasmonic nanostructures tailored by atomic layer deposition

Abstract Atomic layer deposition (ALD) is a powerful technique with the capabilities of conformal deposition and precise thickness control of thin films up to atomic level. In this study, the advantages of ALD are exploited to fabricate plasmonic nanostructures with high chemical resistance and sensitivity. An ultrathin, highly conformal Al2O3 shell layer was deposited by ALD upon Ag nanoparticles for the preparation of Ag/Al2O3 core-shell plasmonic nanostructures. The Al2O3 shell effectively serves as an anti-corrosion protective layer for Ag nanoparticles against the detrimental environment because of its conformal step coverage, pinhole-free structure, and chemical inertness. The shape of the Ag nanoparticles turns into spherical-like particles after the ALD process. An enhancement factor as large as ∼106 of surface-enhanced Raman scattering (SERS) from Ag/Al2O3 core-shell plasmonic nanostructures is achieved, indicating that the plasmonic sensitivity of Ag nanoparticles is not significantly degraded by the ultrathin Al2O3 shell layer. The result demonstrates that the conformal protective layer prepared by ALD facilitates the practical use of plasmonic chips in a variety of applications.

Modeling, Fabrication, and Characterization of 3-D Capacitor Embedded in Through-Silicon Via

A new approach to implement integrated capacitors with an excellent capacitance density, called the “3-D embedded capacitor,” is investigated. It is realized by embedding metal–insulator–metal (MIM) layers onto the trenches of through-silicon vias prior to copper filling. An ultrahigh capacitance density of 5621.8 nF/mm2 was envisioned according to our model, which is $\sim 13\times $ of 440.0 nF/mm2 from a conventional trench capacitor with the same design parameters. A set of prototypes was fabricated and characterized for assessment of structural integrity and electrical performance of the 3-D embedded capacitors. Scanning electron microscope, transmission electron microscope, and energy-dispersive X-ray spectroscopy analysis results show a good step coverage and stoichiometry of the MIM layers deposited. The capacitance density of up to 3856.4 nF/mm2 was achieved for the prototypes with MIM layers formed by atomic layer deposition. A leakage current density as low as $1.61 \times 10^{-7}$ A/cm2 at 4.3 V and a breakdown voltage greater than 9.5 V were measured for a sample with a capacitance density of 3776.6 nF/mm2.

Thermal Reliability Study of an Electrothermal MEMS Mirror

Micro-electrical-mechanical mirrors based on electrothermal bimorph actuators have unparalleled advantages of large scan range, low driving voltage, and high fill factor, but their reliability issues are not well understood. One of the main failure phenomena is the burnout of the refractory metal resistor embedded in electrothermal bimorph actuator structures. In this paper, the burnout process was thoroughly studied via both electrical and optical testing. In particular, the current passing through the embedded resistor was monitored throughout the entire burnout process. It was found that the burnout was caused by multiple steps of anomalies, including electrical breakdown at poor step coverage, short circuit, overheating, and electromigration. Electrical models and lumped-element thermal models were established and electrothermomechanical finite-element method simulations were performed. The modeling and simulation results are all in good agreement with the experimental results. These findings will help greatly improve future design for better reliability.

Deposition and process development of AlN for MEMS acoustic sensor

This paper describes a technique for fabrication of AlN based structure for MEMS acoustic sensor and similar applications. The AlN films of 2.1 μm thickness are grown on silicon substrates by reactive sputtering. The deposited films are characterized to determine the crystalline quality and piezoelectricity. Thermal annealing of the deposited films are performed at different temperatures for better piezoelectricity. The investigation showed a c-axis oriented AlN film is obtained at 600 °C temperature. A simple AlN based structure for MEMS acoustic sensor is fabricated on a thin silicon diaphragm. During fabrication of structure, a wet etching technique of AlN was developed. The reliability testing of fabricated structured was performed. The maximum current that can be passed across Al-deposited AlN edge was found to be 3.05 A without any damage. The investigations show a uniform Al step coverage on a 2.1 μm-thick AlN edge using proposed technique. The proposed technique for AlN etching reduces the process complexity and providing better reliability of fabricated structure. The resonance frequency of fabricated AlN based structure was measured and found to be 42.9 kHz.

Superconformal coating and filling of deep trenches by chemical vapor deposition with forward-directed fluxes

The authors report a superconformal chemical vapor deposition method that affords bottom-up filling of trenches with oxide: the film growth rate increases with depth such that the profile of material develops a “V” shape that fills in along the centerline without a seam of low density material. The method utilizes low pressures of a metal precursor plus a forward-directed flux of co-reactant (water) at a lower pressure than the precursor. Under these conditions, many of the co-reactant molecules travel ballistically to the trench bottom where a fraction of them reflect. This scattering, which creates a virtual source of co-reactant from the trench bottom, leads to a superconformal growth process whose rate is highest at the bottom and declines toward the opening. Simultaneous with this superconformal component is the typical subconformal growth process due to the portion of the co-reactant flux that enters the trench opening isotropically; with a sufficiently large forward-directed flux, however, the overall profile is superconformal. We demonstrate this approach for filling trenches with HfO2 using 0.09 mTorr tetrakis(dimethylamido)­hafnium (TDMA-Hf) precursor and 0.009 mTorr H2O co-reactant. Precursor-rich growth conditions at a substrate temperature of ≤270 °C are used to assure that the growth rate is kinetically limited (determined) by the H2O flux and is nearly independent of the TDMA-Hf flux. Under these conditions, the growth rate in a trench with an aspect ratio of 3.5 increases from 0.6 nm/min at the top to 1.0 nm/min at the bottom sidewalls (step coverage = 1.6). The authors simulate the precursor transport-reaction problem within the trench using a Markov chain model to account for both the forward-directed and isotropic reactant fluxes and for the multiple reemission events within the trench, as a function of the surface sticking probability β of the water flux. The model predicts the fraction of the total incident flux that must be forward-directed in order to afford seam-free filling as a function of the sticking probability and the starting aspect ratio. Experimentally, the authors find that the opening of the trench accumulates a slightly greater thickness (a “bread-loaf” profile) that tends to pinch off the trench just before complete filling. To eliminate this effect, a molecular inhibitor, H(hfac) or H(acac), is used to reduce the growth rate near to the opening. The result is seam-free filling of trenches with HfO2 up to an aspect ratio of 10.

Conformal MgO film grown at high rate at low temperature by forward-directed chemical vapor deposition

MgO thin films are deposited by chemical vapor deposition from the precursor magnesium N,N-dimethylaminodiboranate, Mg(H3BNMe2BH3)2, and water at a substrate temperature of 270–350 °C. Highly conformal coatings with 98% step coverage in trenches of aspect ratio 9 are obtained at a substrate temperature of 270 °C and a growth rate of 7.5 nm/min, most notably through the use of a forward-directed flux, in which some of the precursor molecules travel ballistically down the recessed feature, strike the bottom, and are scattered there to create a virtual source. The deposition conditions can also be adjusted to afford a growth rate up to 200 nm/min with reduced conformality. Most of the films have a dense and column-free microstructure with low surface roughness; the film density, measured by a combination of Rutherford backscattering spectrometry and scanning electron microscopy, is 82%–86% of bulk. Films grown on Si substrates have good adhesion and a low coefficient of friction (∼0.1) in nanoscratch measurements. The refractive index of the films is slightly lower than that of bulk MgO, consistent with the reduced physical densities. Depending on the growth conditions, the C content in the films varies between 0.7 and 6 at. %, and the B content ranges from 1 to 16 at. %. B in the film is present in the B2O3 chemical state; after subtracting the O content in B2O3, the O/Mg ratio = 1.02 in the MgO matrix. A film grown at a temperature of 270 °C and a growth rate of 6 nm/min has a dielectric constant of 9.5 and a breakdown strength of 6 MV/cm.

Effect of thickness on the properties of ZnO thin films prepared by reactive RF sputtering

This work reports structural and electrical properties of ZnO thin film deposited by reactive RF sputtering at the room temperature, for thin film transistor (TFT) applications. To study the thickness dependent effect, ZnO thin film of thicknesses 100, 200 and 800 nm were deposited over p-type silicon substrate. Structural properties of thin films have been characterized using X-ray Diffraction (XRD) and Atomic Force Microscopy (AFM). XRD analysis of 100 and 200 nm thick films shows dominant cubic phase of ZnO along with small presence of ZnO2, while; XRD analysis of 800 nm thick film confirms strong c-axis growth of wurtzite (W) ZnO. The XRD result confirm the polycrystalline nature of the thin film and shows that crystallinity improves with the film thickness. The AFM results confirm high step coverage of deposited thin films. From the thermionic transport model across the grain boundary it was observed that with an increase in film thickness mobility of carriers increases. The sheet resistance of undoped 100 and 200 nm ZnO film is found to be approximately 7 × 1011 Ω/□; while, the sheet resistance of 800 nm thick ZnO film shows almost 10 time reduction to 6.025 × 1010 Ω/□, owing to its improved crystallinity.

Temperature induced interface and optical properties of the multi-layer nanotube network

The ever-increasing demand for larger surface area, well-defined, and conformal multi-layer nanostructures in gas sensor, catalyst and solar cell applications has propelled the exploration of such nanostructures within an atomic resolution. The atomic layer deposition (ALD) technique is ideal for the synthesis of these nanostructures due to its excellent step coverage ability on high aspect ratio nanostructures. In this work, different coaxial nanotube networks are successfully fabricated by electrospinning and ALD, with a well-controlled phase. We systematically studied the temperature-induced microstructures and photoluminescence property evolution of the nanotube network. The Al2O3/ZnO/Al2O3 tri-layer nanotube network is obtained by sintering at 400 °C, and a ZnAl2O4 core-shell nanotube structure has formed by the Kirkendall effect by further post-annealing at 700 °C. Oxygen accumulation is clearly observed at the small neck feature, but the Zn and Al elements are uniformly distributed along the whole nanotube. Photoluminescence emission obtained in this work is so broad that it almost covers the whole visible light wavelength range. The results indicate that the microstructures and photoluminescence properties can be well-controlled by the post-annealing temperature. It provides an available platform for realizing conformal 3D nano-devices.

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.

Remote plasma atomic layer deposition of silicon nitride with bis(dimethylaminomethyl-silyl)trimethylsilyl amine and N2 plasma for gate spacer

The silicon nitride (SiNx) atomic layer deposition with bis(dimethylaminomethylsilyl)-trimethylsilyl amine precursor and N2 remote plasma was investigated. The process window ranged from 250 to 400 °C, and the growth rate was about 0.38 ± 0.02 Å/cycle. The physical, chemical, and electrical characteristics of the SiNx thin films were examined as a function of deposition temperature and plasma power. Based on the results of spectroscopic ellipsometry and x-ray photoelectron spectroscopy, the growth rate and state of binding energy showed little difference depending on the plasma power. The better film properties such as leakage current density and etch resistance were obtained at higher deposition temperatures and higher plasma power. High wet etch resistance (wet etch rate of ∼2 nm/min) and low leakage current density (∼10−8 A/cm2) were obtained. The step coverage, examined by transmission electron microscopy, was about 80% on a trench with an aspect ratio of 4.5.

Highly conformal carbon-doped SiCN films by plasma-enhanced chemical vapor deposition with enhanced barrier properties

A plasma-enhanced chemical vapor deposition (PECVD) was developed for the growth of highly conformal carbon-doped silicon nitride (SiCN) films with enhanced barrier properties drawing on tunable carbon contents, k-values, and wet etch rates (WER). Trisilylamine (TSA) was used as the main precursor and hexane was used as a hydrocarbon-containing additive precursor for carbon doping. At low deposition temperatures ≤ 400 °C, we show that this PECVD process leads to the formation of SiCN films with good conformality of approximately 91% over high aspect ratio trench nanostructures (4.2:1) with a growth rate of ~2.5 (Å/cycle). In particular, the role of TSA and hexane precursors on the film growth mechanism and the k-values, and WER in the composite structures has been explored. The precursors were introduced pulse-wise into the reaction chamber while plasma was excited. The WER of the film was evaluated in a buffered hydrofluoric acid etchant. The k-value and carbon concentration varied depending on the TSA/hexane supply time in the ranges of 7–4.5 and around 6–40%, respectively. Analysis showed that the hexane precursor improved the WER of deposited SiCN films by more than a factor of 100 compared to when only TSA was used. The SiCN film with a thickness of 5.0 nm exhibited excellent prevention of moisture diffusion into the device. Furthermore, the step coverage was improved to equivalent conformality of the plasma-enhanced atomic layer deposition (PEALD) by modifying the supply method of the Si and carbon precursors and the moisture barrier property was secured with thicknesses of <10 nm. In particular, the Si and carbon precursors are biased to maximize the process margin and control the film characteristics, where tuning can be easily implemented.

Leakage current suppression in spatially controlled Si-doped ZrO2 for capacitors using atomic layer deposition

Among various high-k materials, zirconium dioxide (ZrO2) has attracted considerable attention due to its high dielectric constant and wide band gap. However, its main disadvantage of ZrO2 films which have tetragonal phase is its large leakage current along grain boundaries. Doping ZrO2 with silicon has been proposed as a solution to this issue.In this study, we investigated the electronic structure of Si-doped ZrO2 thin films. We used atomic layer deposition to deposit Si-doped ZrO2 thin films. This method has many advantages such as excellent step coverage, low process temperature, and ultrathin growth. We found that proper Si doping, which affects Si distribution in the ZrO2 and therefore its electronic band structure, is necessary for leakage current reduction.

(Invited) Atomic Layer Deposition for Interface Engineering of (Thin-Film) Lithium-Ion Battery

Atomic layer deposition (ALD) is a gas-phase deposition technique based on sequential self-limiting surface reactions [1]. The self-limiting nature of these gas-surface interactions give ALD several advantages over other deposition techniques if exploited properly: excellent conformality on and in 3D-structured substrates (powders, pores, trenches [2]), smooth and pinhole-free films and ultimate thickness control (~0.1nm precision). These near-unique advantages can be exploited to advance energy storage devices, lithium-ion batteries foremost amongst them [3,4]. On the one hand the excellent step coverage inherent to atomic layer deposition can be exploited to construct complex engineered micro- and nano-structured batteries. These 3D thin-film nano- and microbatteries are interesting storage modes for electronics thanks to their relatively high capacity and very high power densities [5-6]. However, ALD is not without disadvantages. The slow deposition rate (0.1nm/s-0.1nm/min) and high cost compared to for example wet chemical deposition methods typically prevent a full battery stack grown with ALD from being commercially viable. The real strength of ALD lies not in the micron-thick films needed for the electrodes in a thin-film battery, but rather in thin films in the range of 0.1nm to 100nm. An electrochemical storage system consists of many interfaces, and most of the important phenomena occur at those interfaces. Tuning or engineering of these interfaces can be of paramount importance to enhance battery characteristics or unlock novel battery chemistries. In that respect, ALD can be used to deposit conductive coatings as current collector on non-conductive scaffolds, seed layers to enable adhesion or prevent current collector oxidation, protective coatings at the electrode/liquid electrolyte interface and solid electrolytes to prevent the liquid electrolyte all together [3,4]. In this talk, two examples will be highlighted. Firstly, ALD has been heavily investigated for electrode/electrolyte interface engineering since 2010, with the main focus on ALD of Al2O3, given the ease of deposition and proven scalability of this process. However, using model-system thin film electrodes, we can show that ALD Al2O3 films beyond 3nm are completely blocking towards Li+ ions, while thinner coatings impose a significant impedance of >1012 Ω cm. ALD TiO2 on the other hand is shown to be not blocking towards Li+ ions, and can alleviate solvent decomposition or metal dissolution, two important capacity fading mechanisms found at this interface [5,7]. Secondly, electrolytic manganese oxide (EMD) and its converted form to LiMn2O4 (LMO) are considered interesting cathode materials. However, the electrodeposition of thick films of EMD is challenged by film adhesion and current collector oxidation of non-noble current collectors (eg TiN or Ni), limiting the deposition of and electrochemically active film in acidic electrolytes to approx. 50nm. It is shown that using an ALD MnO2 seed layer of only a 2-4 nm, the adhesion was improved and substrate oxidation was alleviated, allowing electrochemically active EMD films up to 1µm. This could also be demonstrated on 3D-structured substrates, thanks to the conformal nature of both electrodeposition and ALD [8]. In conclusion, despite the slow deposition rates typical for ALD, it can be used as a powerful tool in engineering of interfaces in lithium-ion battery development. [1] George, S. M., Ott, A. W. & Klaus, J. W. Surface Chemistry for Atomic Layer Growth. J. Phys. Chem. 100, 13121–13131 (1996). [2] Detavernier, C., Dendooven, J., Sree, S. P., Ludwig, K. F. & Martens, J. A. Tailoring nanoporous materials by atomic layer deposition. Chem. Soc. Rev. 40, 5242–5253 (2011). [3] Meng, X., Yang, X.-Q. & Sun, X. Emerging Applications of Atomic Layer Deposition for Lithium-Ion Battery Studies. Adv. Mater. 24, 3589–3615 (2012). [4] Liu, J. & Sun, X. Elegant design of electrode and electrode/electrolyte interface in lithium-ion batteries by atomic layer deposition. Nanotechnology 26, 024001 (2015). [5] Kurttepeli, M. et al. Heterogeneous TiO2/V2O5/Carbon Nanotube Electrodes for Lithium-Ion Batteries. ACS Appl. Mater. Interfaces 9, 8055–8064 (2017). [6] Mattelaer, F., Geryl, K., Rampelberg, G., Dendooven, J. & Detavernier, C. Amorphous and Crystalline Vanadium Oxides as High-Energy and High-Power Cathodes for Three-Dimensional Thin-Film Lithium Ion Batteries. ACS Applied Materials & Interfaces 9, 13121–13131 (2017). [7] Mattelaer, F., Vereecken, P. M., Dendooven, J. & Detavernier, C. The Influence of Ultrathin Amorphous ALD Alumina and Titania on the Rate Capability of Anatase TiO2 and LiMn2O4 Lithium Ion Battery Electrodes. Advanced Materials Interfaces 1601237 (2017). [8] Timmermans, M. Y. et al. Electrodeposition of Adherent Submicron to Micron Thick Manganese Dioxide Films with Optimized Current Collector Interface for 3D Li-Ion Electrodes. J. Electrochem. Soc. 164, D954–D963 (2017).