Atomic Layer Deposition Window Research Articles

Two-step ALD process for non-oxide ceramic deposition: the example of boron nitride

Atomic layer deposition (ALD) based on polymer-derived ceramics (PDCs) chemistry is used for the fabrication of boron nitride thin films from reaction between trichloroborazine and hexamethyldisilazane. The transposition of the PDCs route to ALD is highly appealing for depositing ceramics, especially non-oxide ones, as it offers various molecular precursors. From a two-step approach composed of an ALD process forming a so-called preceramic film and its subsequent ceramization, conformal and homogenous BN layers are successfully synthesized on various inorganic substrates. In the first stage, smooth polyborazine coatings are obtained at a temperature as low as 90 °C. The saturation and self-limitation of the ALD gas-surface reactions are verified. Intriguingly, three ALD windows seem to exist and are attributed to change in ligand exchange. After the ceramization stage using a heat treatment, conformal near-stoichiometric BN layers are obtained. Their structure in terms of crystallinity can be adjusted from amorphous to well-crystalline sp2 phase by controlling the treatment temperature. In particular, a crystallization onset occurs at 1000 °C and well defined sp2 crystalline planes oriented parallel to the surface are noted after ceramization at 1350 °C. Finally, side-modification of the substrate surface induced by the thermal treatment appears to impact on the final BN topography and defect generation.

Tailoring indium oxide film characteristics through oxygen reactants in atomic layer deposition with highly reactive liquid precursor

Indium oxide (InOx) films were deposited via atomic layer deposition (ALD) using a novel liquid indium precursor, dimethyl[N1-(tert-butyl)–N2,N2-dimethylethane-1,2-diamine]indium (DMITN). In this process, the reactant (H2O, O3, or O2 plasma) and substrate temperature (100–250 ℃) were varied. The DMITN precursor showed excellent reactivity with all three reactants. The growth characteristics (ALD window, growth per cycle, and step coverage) and film properties (impurities, stoichiometry, oxygen bonding state, crystallinity, film density, and electrical properties) differed based on the ALD process employed, ascribed to the distinct thermal energies and inherent reactivities of the chosen oxidants. As the oxidation energy of the reactants increased (H2O < O3 < O2 plasma), the growth per cycle (GPC) and the oxygen–indium bond ratio of InOx increased. Crystallinity analysis also revealed significant differences depending on the reactants, where the Hall mobility was predominantly influenced by the crystal alignment. The step coverage at an aspect ratio of 40:1 was markedly superior with the use of H2O and O3 reactants (approximately 95 %) compared to that with O2 plasma (approximately 74 %). These findings highlight the capability of controlling the growth and properties of InOx films by judiciously selecting the reactant, emphasizing the versatility of the DMITN precursor in ALD processes.

Atomic Layer Deposition of NiO Using Different Precursors with Different Oxygen Sources

NiO thin films have attracted tremendous attention owing to their outstanding chemical stability, good magnetic and catalytic properties1. It is also considered an efficient electrocatalyst for water oxidation, and is one of the few p-type semiconductive oxides with optical transparency due to its wide bandgap of 3.6 eV. Furthermore, NiO films can control high and low conductive states under an external electric field, which is very useful for developing resistance-switching random-access memory devices2.NiO films have been prepared by different deposition techniques, including sputtering, sol-gel, pulsed laser deposition, spray pyrolysis, and chemical vapor deposition (CVD), atomic layer deposition (ALD). Among these, ALD is a powerful technique to grow thin conformal films with fine-tuning of both composition and thickness. The commonly used nickel precursors for ALD process are Ni(Cp)2, Ni(MeCp)2, Ni(EtCp)2, Ni(dmamp)2, Ni(dmamb)2, Ni(acac)2, Ni(apo)2, Ni(dmg)2, Ni(thd)2, and Ni(amd)2 in combination with ozone, water, hydrogen peroxide, or oxygen plasma1. However, ALD of NiO is not well developed yet. The major disadvantages associated with these nickel precursors are low volatility, thermal instability, and poor reactivity or narrow ALD window. Some of these precursors are expensive or very difficult to synthesize. The aforementioned situations indicate that developing a new ALD process for the NiO film with new precursors is pertinent.In this work, we explored different Ni-precursors such as Ni ketoiminates, Ni(ipki)2 and Ni(eeki)2 (their synthesis has been proposed earlier3), and Alanis, provided by Air Liquide. These different reactants combined with different oxygen sources (H2O and O3) resulted in high-quality NiO thin films. Surface analyses indicate NiO films are stoichiometric. They are uniform and exhibit a columnar morphology as determined by TEM (Fig.1a). From the growth characteristics, it is found that the Ni precursors have a strong effect on the GPC. Similarly, the oxygen source affects GPC but it also influences the morphology of the layer leading to significant roughness variations (observed by XRR and AFM). The use of H2O can also result in a nucleation delay. Polycrystalline films are observed when the reaction temperature reaches 125°C, and the crystallinity is further enhanced with deposition temperature (Fig.1b). After comprehensive optimization of the ALD process with Alanis precursor, it has been possible to reach one of the highest growth rate of 1.5 Å/cy, which is nearly seven times higher than that obtained with Ni(EtCp)2 based reaction with the same ALD reactor and having a wide temperature window (100 to 175 °C) with ozone. The same precursor also reacted well with water, giving a GPC of 0.9 Å with an initial nucleation delay. With the use of Ni-ketoiminates, the growth rate could be enhanced considerably with a GPC of 0.7 Å in combination with O3 at a higher temperature.The NiO layers were subsequently used as catalysts for water photooxidation in alkaline medium. The electrochemical properties are better when compared to layers grown by PVD. References Y. Zhang, L. Du, X. Liu, and Y. Ding, A high growth rate atomic layer deposition process for nickel oxide film preparation using a combination of nickel (II) diketonate-diamine and ozone, App. Surf. Sci., 2019, 481, 138-143.H.L. Lu, G. Scarel, X.L. Li, M. Fanciulli, Thin MnO and NiO films grown using atomic layer deposition from ethylcyclopentadienyl type of precursors, J. Cryst. Growth, 2008, 310, 5464-5468.3. D. Zywitzki, D.H. Taffa, L. Lamkowski, M. Winter, D. Rogalla, M. Wark, and A. Devi, Tuning coordination geometry of nickel ketoiminates and its influence on thermal characteristics for chemical vapour deposition of nanostructured NiO electrocatalysts, Inorg. Chem., 2020,59, 14, 10059-10070. Figure 1

A Novel Approach to Obtaining Metal Oxide HAR Nanostructures by Electrospinning and ALD

In this work, a novel approach is suggested to grow bilayer fibers by combining electrospinning and atomic layer deposition (ALD). Polyvinyl alcohol (PVA) fibers are obtained by electrospinning and subsequently covered with thin Al2O3 deposited at a low temperature by ALD. To burn the PVA core, the fibrous structures are subjected to high-temperature annealing. Differential scanning calorimetry (DSC) analysis of the PVA mat is performed to establish the proper annealing regime for burning off the PVA core and obtaining hollow fibers. The hollow fibers thus formed are covered with a ZnO layer deposited by ALD at a higher temperature within the ALD window of ZnO. This procedure allows us to prepare ZnO films with better crystallinity and stoichiometry. Different characterization methods—SEM, ellipsometry, XRD, and XPS—are performed at each step to investigate the processes in detail.

New Heteroleptic Germanium Precursors for GeO2 Thin Films by Atomic Layer Deposition.

This study describes the synthesis of 12 new germanium complexes containing β-diketonate and/or N-alkoxy carboxamidate-type ligands as precursors for GeO2 through atomic layer deposition (ALD). A series of Ge(β-diketonate)Cl complexes such as Ge(acac)Cl (1) and Ge(tmhd)Cl (2) were synthesized by using acetylacetone (acacH) and 2,2,6,6-tetramethyl-3,5-heptanedione (tmhdH). N-Alkoxy carboxamidate-type ligands such as N-methoxypropanamide (mpaH), N-methoxy-2,2-dimethylpropanamide (mdpaH), N-ethoxy-2-methylpropanamide (empaH), N-ethoxy-2,2-dimethylpropanamide (edpaH), and N-methoxybenzamide (mbaH) were used to afford further substituted complexes Ge(acac)(mpa) (3), Ge(acac)(mdpa) (4), Ge(acac)(empa) (5), Ge(acac)(edpa) (6), Ge(acac)(mba) (7), Ge(tmhd)(mpa) (8), Ge(tmhd)(mdpa) (9), Ge(tmhd)(empa) (10), Ge(tmhd)(edpa) (11), and Ge(tmhd)(mba) (12), respectively. Thermogravimetric analysis curves, which mostly exhibited single-step weight losses, were used to determine the evaporation properties of complexes 1-12. Interestingly, liquid complex 2 has no residue at 198 °C and therefore exhibits excellent vaporization properties and high volatility. Single-crystal X-ray diffraction studies of 1 and 7 demonstrated that the complexes had monomeric molecular structures with germanium chelated by the oxygen atoms of one or two bidentate ligands, respectively. An ALD process was developed for the growth of GeO2 using Ge(tmhd)Cl (2) as a new precursor and H2O2 as an oxidant. This study demonstrates the achievement of self-limiting growth of GeO2 films by varying the duration of injection/purge, with an observed ALD window at deposition temperatures ranging from 300 to 350 °C. The saturated growth per cycle of the GeO2 film was determined as 0.27 Å/cycle at a deposition temperature of 300 °C. The deposited films were observed to be amorphous consisting of GeO2.

Low-resistivity molybdenum obtained by atomic layer deposition

A novel atomic layer deposition (ALD) process was developed for low-resistivity molybdenum (Mo) from molybdenum dichloride dioxide (MoCl2O2) and atomic hydrogen (at-H). A wide ALD window of self-limiting growth was observed between 150 and 450 °C. No film deposition occurred with molecular hydrogen (H2), demonstrating the necessity to have at-H to efficiently reduce the MoCl2O2 precursor. At 350 °C and above, the film composition was determined at approximately 95 at. % of Mo and 3.5 at % of oxygen (O), with trace amounts (i.e., &amp;lt;1 at. %) of carbon (C), chlorine (Cl), hydrogen (H), and nitrogen (N). The growth per cycle (GPC) was roughly 0.022 nm/cycle. No substrate selectivity or pronounced nucleation delay was observed on silicon (Si), silicon dioxide (SiO2), silicon nitride (Si3N4), silicon carbide (SiC), aluminum oxide (Al2O3), hafnium dioxide (HfO2), and low-k dielectric (SiOC). Film uniformity and conformality were ±5% and ±10%, respectively, while resistivity approached a bulk value of 18.6 μ Ω cm at 24 nm. At 250 °C and below, increased levels of oxygen (up to 33 at. % at 150 °C) and chlorine (2.7 at. % at 150 °C) were detected in the film. This trend coincided with an increase in the GPC, a change in optical properties, a decrease in film density and crystallinity, and an increase in resistivity. While self-limiting growth was observed through the entire ALD window of 150–450 °C, the temperature (T) range for depositing low-resistivity Mo deposition was narrower at T ≥ 250 °C.

Low temperature atomic layer deposition of cobalt using dicobalt hexacarbonyl-1-heptyne as precursor.

In this work, we present the development of an atomic layer deposition (ALD) process for metallic cobalt. The process operates at low temperatures using dicobalt hexacarbonyl-1-heptyne [Co2(CO)6HC≡CC5H11] and hydrogen plasma. For this precursor an ALD window in the temperature range between 50 and 110 °C was determined with a constant deposition rate of approximately 0.1 Å/cycle. The upper limit of the ALD window is defined by the onset of the decomposition of the precursor. In our case, decomposition occurs at temperatures of 125 °C and above, resulting in a film growth in chemical vapour deposition mode. The lower limit of the ALD window is around 35 °C, where the reduction of the precursor is incomplete. The saturation behaviour of the process was investigated. X-ray photoelectron spectroscopy measurements could show that the deposited cobalt is in the metallic state. The finally established process in ALD mode shows a homogeneous coating at the wafer level.

Thermal atomic layer deposition of molybdenum carbide films using bis(ethylbenzene)molybdenum and H2

To fully exploit the excellent characteristics of molybdenum carbide (MoCx) for advanced semiconductor applications, which require high conformality and very low thickness, the atomic layer deposition (ALD) of MoCx must be developed. In this study, the thermal ALD of MoCx was investigated for the first time using halogen-free bis(ethylbenzene)molybdenum (BEBMo) and H2 (4% in 96% Ar) at deposition temperatures ranging between 180 and 280 °C. ALD MoCx films prepared using BEBMo and H2 exhibited an ALD window of 200−240 °C, moderate growth of 0.034 nm/cycle, and high conformality (∼91%) on the trench substrate. Chemical analysis revealed that the ALD MoCx films predominantly consisted of Mo2C (Mo2+ oxidation state) with a Mo/C atomic ratio of 1.25 and 4% oxygen as an impurity. The as-deposited MoCx films were amorphous at all deposition temperatures, but they crystallized to hexagonal β-Mo2C after post-deposition annealing (PDA) at 600 and 700 °C. The resistivity of the as-deposited MoCx films grown at 250 °C was only 171 μΩ cm at 23 nm, but the resistivity significantly increased to 711 μΩ cm as the film thickness decreased to 4.4 nm. After PDA at 700 °C, the MoCx films showed remarkably low resistivities of 73−104 μΩ cm in the thickness range of 5−23 nm.

(Invited) Energy Enhanced Atomic Layer Deposition (EEALD)

Atomic layer deposition (ALD) is a layer by layer chemical vapor deposition (CVD) technique based on alternating purge-separated self-limiting surface reactions. ALD offers inherent atomic scale controlled growth of high quality conformal thin films at relatively low temperatures. A low thermal budget is often critical in microelectronics processing, such as for back-end-of-line processing, 3D integration, deposition on glass or flexible substrates for large area electronics, avoiding unwanted diffusion, and maintaining stable flat band voltages, effective work functions, threshold voltages, and effective oxide thickness in metal/insulator/metal (MIM) and metal/oxide/semiconductor (MOS) device structures. However, low deposition temperature can lead to incorporation of excess -OH groups or other residual impurities from unreacted ligands and result in poor stoichiometry of ALD films. Poor stoichiometry may in turn lead to sub-optimal physical, optical, and electrical properties. A number of approaches may be used to reduce impurities, increase density, improve properties, and achieve the desired morphology of ALD films. An obvious approach is to increase deposition temperature, however this may move a process out of the ALD window into the CVD regime, negating many of the benefits of ALD. The most common approach is post-deposition annealing (PDA) at elevated temperatures. The PDA temperatures that are typically required however, can exceed the maximum temperature limitations of the substrate or previously formed electronics. To maintain the low thermal budget of ALD while maximizing film properties, performing annealing during, rather than after, deposition can be beneficial. An alternate approach to help drive reactions and reduce impurity / ligand incorporation is thus to add extra energy as part of each (or every few) ALD supercycles. Methods to date include in-situ rapid thermal (MTA, DADA, etc.) annealing, flash lamp annealing, plasma exposure, and UV exposure. I will collectedly refer to these techniques as energy enhanced ALD (EEALD). [1-13] (Note that these methods are distinct from plasma enhanced ALD (PEALD), an excellent review of which can be found in [14].) Documented benefits of the various forms of EEALD include higher GPC, denser films, lower temperature, improved dielectric constant and refractive index, lower leakage, lower residual impurities. A potential downside of energy enhancement is the additional time required to implement these steps into the ALD super-cycle, particularly cool down time when in-situ annealing is incorporated. This invited talk will describe, compare, and contrast these various techniques focusing on mechanisms (thermal vs. chemical), placement in ALD supercycle, benefits and drawbacks, and challenges to be addressed in finding the ideal EE-ALD technique. Finally, I will introduce an entirely new method of EE-ALD. J.F. Conley, Jr., Y. Ono, D.J. Tweet, Appl. Phys. Lett. 84(11), 1913-1915 (2004).J.F. Conley, Jr., D.J. Tweet, Y. Ono, and G. Stecker, in High-k Insulators and Ferroelectrics for Advanced Microelectronic Devices, R.M. Wallace, D. Landheer, M. Houssa, and J. Morais, eds., MRS Proc. Vol. 811, 5 (2004).J.F. Conley, Jr., Y. Ono, D. Tweet, G. Stecker, R. Solanki, and W.W. Zhuang, in Physics and Technology of High-k Gate Diectrics II, S. Kar, R. Singh, D. Misra, H. Iwai, M. Houssa, J. Morais, and D. Landheer, eds., ECS Proc. Vol. 2003-22, 11 pgs.K.H. Holden, S.M. Witsel, P.C. Lemaire, and J.F. Conley, Jr. in preparation (2022).Henke et al., ECS J. Sol. Sta. Sci. Tech. 4(7), 277 (2015).R.D. Clark et al., ECS Transactions, 41(2), 79 (2011).Miikkulainen et al., ECS Tran. 80(3), 49 (2017).Chalker et al., ECS Tran. 69(7), 139 (2015).Kwak, Y.-H. Lee, and B.-H. Choi, Appl. Surf. Sci. 230, 249 (2004).Kim et al., Electrochemical and Solid-State Lett. 14(4), H146 (2011)No et al., J. ECS 153(6), F87 (2006).Shih et al., Sci. Rep. 7(1), 39717 (2017).Österlund et al. Vac. Sci. Tech. A 39, 032403 (2021).Ueda et al., Appl. Surf. Sci. 554, 149656 (2021).Profijt, et al., J. Vac. Sci. Technol. A 29(5), 050801 (2011).

Plasma-enhanced atomic-layer-deposited indium oxide thin film using a DMION precursor within a wide process window

In this study, we developed a new liquid indium precursor, dimethyl[N-(tert-butyl)-2-methoxy-2-methylpropan-1-amine] indium (DMION), to deposit indium oxide films using the plasma-enhanced atomic layer deposition (PEALD) method. The indium oxide films were deposited using DMION and Ar/O2 plasma as the precursor and reactant, respectively, with relatively high growth per cycle (GPC, ∼1.2 Å/cycle) within a wide atomic layer deposition (ALD) window (35–300 °C). Impurities such as carbon and nitrogen were not detected regardless of the deposition temperature. The crystallinity of the films had a bixbyite cubic structure within the ALD window and facets could be controlled by deposition temperature modulation; (400) facets were dominant at low deposition temperatures (35 and 100 °C), whereas (222) facets were dominant at high deposition temperatures (200 and 300 °C). The dominant facets and orientations of the indium oxide crystal were maintained until 400 °C in the post-annealing process. The thin-film transistors (TFTs) using indium oxide deposited at 200 °C exhibited high field-effect (∼32.1 cm2/Vs) mobility with a reasonable threshold voltage (∼1.8 V) and subthreshold voltage swing (∼0.48 V/decade).

Plasma Enhanced Atomic Layer Deposition of Tantalum (V) Oxide

The tantalum oxide thin films are promising materials for various applications: as coatings in optical devices, as dielectric layers for micro and nanoelectronics, and for thin-films solid-state lithium-ion batteries (SSLIBs). This article is dedicated to the Ta-O thin-film system synthesis by the atomic layer deposition (ALD) which allows to deposit high quality films and coatings with excellent uniformity and conformality. Tantalum (V) ethoxide (Ta(OEt)5) and remote oxygen plasma were used as tantalum-containing reagent and oxidizing co-reagent, respectively. The influence of deposition parameters (reactor and evaporator temperature, pulse and purge times) on the growth rate were studied. The thickness of the films were measured by spectroscopic ellipsometry, scanning electron microscopy and X-ray reflectometry. The temperature range of the ALD window was 250–300 °C, the growth per cycle was about 0.05 nm/cycle. Different morphology of films deposited on silicon and stainless steel was found. According to the X-ray diffraction data, the as-prepared films were amorphous. But the heat treatment study shows crystallization at 800 °C with the formation of the polycrystalline Ta2O5 phase with a rhombic structural type (Pmm2). The results of the X-ray reflectometry show the Ta-O films’ density is 7.98 g/cm3, which is close to the density of crystalline Ta2O5 of the rhombic structure (8.18 g/cm3). The obtained thin films have a low roughness and high uniformity. The chemical composition of the surface and bulk of Ta-O coatings was studied by X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy. Surface of the films contain Ta2O5 and some carbon contamination, but the bulk of the films does not contain carbon and any precursor residues. Cyclic voltammetry (CVA) showed that there is no current increase for tantalum (V) oxide in a potential window of 3–4.2 V and has prospects of use as protective coatings for cathode materials of SSLIBs.

Structural Properties of Thin ZnO Films Deposited by ALD under O-Rich and Zn-Rich Growth Conditions and Their Relationship with Electrical Parameters.

The structural, optical, and electrical properties of ZnO are intimately intertwined. In the present work, the structural and transport properties of 100 nm thick polycrystalline ZnO films obtained by atomic layer deposition (ALD) at a growth temperature (Tg) of 100–300 °C were investigated. The electrical properties of the films showed a dependence on the substrate (a-Al2O3 or Si (100)) and a high sensitivity to Tg, related to the deviation of the film stoichiometry as demonstrated by the RT-Hall effect. The average crystallite size increased from 20–30 nm for as grown samples to 80–100 nm after rapid thermal annealing, which affects carrier scattering. The ZnO layers deposited on silicon showed lower strain and dislocation density than on sapphire at the same Tg. The calculated half crystallite size (D/2) was higher than the Debye length (LD) for all as grown and annealed ZnO films, except for annealed ZnO/Si films grown within the ALD window (100–200 °C), indicating different homogeneity of charge carrier distribution for annealed ZnO/Si and ZnO/a-Al2O3 layers. For as grown films the hydrogen impurity concentration detected via secondary ion mass spectrometry (SIMS) was 1021 cm−3 and was decreased by two orders of magnitude after annealing, accompanied by a decrease in Urbach energy in the ZnO/a-Al2O3 layers.

Properties and Mechanism of PEALD-In2O3 Thin Films Prepared by Different Precursor Reaction Energy.

Indium oxide (In2O3) film has excellent optical and electrical properties, which makes it useful for a multitude of applications. The preparation of In2O3 film via atomic layer deposition (ALD) method remains an issue as most of the available In-precursors are inactive and thermally unstable. In this work, In2O3 film was prepared by ALD using a remote O2 plasma as oxidant, which provides highly reactive oxygen radicals, and hence significantly enhancing the film growth. The substrate temperature that determines the adsorption state on the substrate and reaction energy of the precursor was investigated. At low substrate temperature (100–150 °C), the ratio of chemically adsorbed precursors is low, leading to a low growth rate and amorphous structure of the films. An amorphous-to-crystalline transition was observed at 150–200 °C. An ALD window with self-limiting reaction and a reasonable film growth rate was observed in the intermediate temperature range of 225–275 °C. At high substrate temperature (300–350 °C), the film growth rate further increases due to the decomposition of the precursors. The resulting film exhibits a rough surface which consists of coarse grains and obvious grain boundaries. The growth mode and properties of the In2O3 films prepared by plasma-enhanced ALD can be efficiently tuned by varying the substrate temperature.

Atomic-layer deposition of TiO2 thin films with a thermally stable (CpMe5)Ti(OMe)3 precursor

Atomic layer deposition (ALD) of TiO2 films from (CpMe5)Ti(OMe)3 as precursor and O3 as co-reactant was examined. The high thermal stability of (CpMe5)Ti(OMe)3 enabled ALD reaction up to a high temperature of 345 °C. A wide temperature window from 182 to 345 °C was achieved in the ALD process, and the growth per cycle increased with increasing the temperature from 0.025 to 0.06 nm/cycle in the ALD window. The impurity content of the films decreased with increasing growth temperature. Above 291 °C, the carbon content in the films decreased to the level in a single crystalline Si substrate. The morphology with patterns spreading radially from the multiple points developed above 236 °C, and the size of the grains decreased as the growth temperature increased. Eventually, a uniform morphology with fine grains was obtained at temperatures > 300 °C. The films grown at the high temperatures exhibited superior dielectric properties. Other common metalorganic precursors of Ti usually restrict the use of high-temperature ALD because they are thermally unstable and decompose below 300 °C. Therefore, (CpMe5)Ti(OMe)3 is favorable for forming dense and high-purity TiO2 films by ALD.

In situ ellipsometry monitoring of TiO[formula omitted] atomic layer deposition from Tetrakis(dimethylamido)titanium(IV) and H[formula omitted]O precursors on Si and In[formula omitted]Ga[formula omitted]As substrates

TiO2 Atomic Layer Deposition (ALD) is used in microelectronics due to its ability to produce conformal thin films whose thickness is controlled at the sub-nanometer scale. Tetrakis(dimethylamido)titanium(IV) and water are frequently used precursors for TiO2 ALD, although there are still some differences in growth behavior in the literature. In this parametric study, the growth of TiO2 was controlled in situ by Multi-Wavelength Ellipsometry in combination with ex situ thickness measurements by X-ray Reflectometry. The injection and purge times were optimized to reach self-saturation on the surface. We put in evidence two regions of the Growth Per Cycle (GPC) as a function of substrate temperature: GPC decreases from 0.8 Å cy−1 to 0.5 Å cy−1 as the temperature rises from 50 °C to 200 °C, and then GPC increases from 0.6 Å cy−1 to 0.9 Å cy−1 as the temperature rises from 250 °C to 350 °C. There is no evidence of an ALD window - the temperature region where the growth rate is the same. The stoichiometry of the layer grown at 200 °C, determined by X-ray Photoelectron Spectroscopy, is TiO2 (1 Ti atom per 2 O atoms). The 200 °C as-grown sample becomes crystalline (Anatase crystals) after annealing 3 h in air at 400 °C, or at 600 °C. The initial growth stages of TiO2 were studied by Multi-Wavelength Ellipsometry and Atomic Force Microscopy. Regarding TiO2 ALD on (100)Si substrate (with a native SiO2), we observed a substrate enhanced growth which turned into steady-state ALD beyond 20–30 cycles. Additionally, TiO2 ALD on (001)In0.53Ga0.47As substrate demonstrates substrate inhibited growth of type 2 (islands formation) which turned into TiO2 steady-state ALD beyond 20–30 cycles. The results of TiO2 ALD are compared with those of the existing literature.

Atomic layer deposition of titanium dioxide films using a metal organic precursor (C12H23N3Ti) and H2O (DI water)

We investigated the deposition of titanium dioxide (TiO2) thin films. TiO2 thin films were deposited using flow-type atomic layer deposition (ALD) and the new MAP Ti (C12H23N3Ti) precursor and deionized water (DI) as a reactant. For the deposition of TiO2 thin films using the new Ti precursor and DI, the ALD window was between 250 °C and 275 °C, which is lower than the ALD window using conventional metal organic Ti precursors. X-ray photoelectron spectroscopy (XPS) analysis showed that the Ti:O ratio was about 1:1.8. Additionally, there were almost no impurities in the thin film, confirming that TiO2 thin film was deposited with the proposed method. After heat treatment of thin films in the range of 400 °C–800 °C, X-ray diffraction (XRD) measurements were conducted. When the heat treatment was performed at 700 °C, a mixed anatase and rutile phase appeared. However, when the heat treatment was done at 800 °C, the anatase phase disappeared and only the rutile phase was obtained. Based on C–V and I–V analyses, dielectric constant values from 32 to 94 were obtained as the heat treatment temperature increased. Additionally, the leakage current was 10−5 A/cm2, which is superior to previously reported TiO2 thin films.

Thermal and Plasma-Enhanced Atomic Layer Deposition of Yttrium Oxide Films and the Properties of Water Wettability.

The atomic layer deposition (ALD) of yttrium oxide (Y2O3) is investigated using the liquid precursor Y(EtCp)2(iPr-amd) as the yttrium source with thermal (H2O) and plasma-enhanced (H2O plasma and O2 plasma) processes, respectively. Saturation is confirmed for the growth of the Y2O3 films with each investigated reactant with a similar ALD window from 150 to 300 °C, albeit with a different growth rate. All of the as-deposited Y2O3 films are pure and smooth and have a polycrystalline cubic structure. The as-deposited Y2O3 films are hydrophobic with water contact angles >90°. The water contact angle gradually increased and the surface free energy gradually decreased as the film thickness increased, reaching a saturated value at a Y2O3 film thickness of ∼20 nm. The hydrophobicity was retained during post-ALD annealed at 500 °C in static air for 2 h. Exposure to polar and nonpolar solvents influences the Y2O3 water contact angle. The reported ALD process for Y2O3 films may find potential applications in the field of hydrophobic coatings.

Thermal atomic layer deposition of ruthenium metal thin films using nonoxidative coreactants

Atomic layer deposition (ALD) of ruthenium metal films is presented using (η4-2,3-dimethylbutadiene)(tricarbonyl)ruthenium [Ru(DMBD)(CO)3] with the coreactants 1,1-dimethylhydrazine, hydrazine, or tert-butylamine. The dependence of growth rate on precursor pulse lengths at 200 °C showed a saturative, self-limited behavior at ≥3.0 s for Ru(DMBD)(CO)3 and ≥0.1 s for 1,1-dimethylhydrazine. An ALD window was observed from 200 to 210 °C, with a growth rate of 0.42 Å/cycle. Films grown at 200 °C showed rms surface roughnesses of &amp;lt;1 nm. X-ray photoelectron spectroscopy of a 42 nm thick film grown at 200 °C revealed 90.6% ruthenium, 7.0% nitrogen, and 2.0% oxygen. Ruthenium films were deposited on patterned substrates with TiN surfaces using various treatments at 200 °C with 250 cycles. 42 nm thick ruthenium films grown at 200 °C were subjected to annealing studies under hydrogen and ammonia atmospheres at 400 °C, followed by rapid thermal annealing at 600 °C. These annealing procedures led to higher purity, more crystalline, and lower resistivity ruthenium films. The coreactants hydrazine and tert-butylamine were evaluated in ruthenium ALD trials using Ru(DMBD)(CO)3. Hydrazine gave a growth rate of 0.42 Å/cycle within a 200–205 °C ALD window, whereas tert-butylamine gave a growth rate of 0.25 Å/cycle at 200 °C.

Low-Temperature Atomic Layer Deposition of Highly Conformal Tin Nitride Thin Films for Energy Storage Devices.

We present an atomic layer deposition (ALD) process for the synthesis of tin nitride (SnNx) thin films using tetrakis(dimethylamino) tin (TDMASn, Sn(NMe2)4) and ammonia (NH3) as the precursors at low deposition temperatures (70-200 °C). This newly developed ALD scheme exhibits ideal ALD features such as self-limited film growth at 150 °C. The growth per cycle (GPC) was found to be ∼0.21 nm/cycle at 70 °C, which decreased with increasing deposition temperature. Interestingly, when the deposition temperature was between 125 and 180 °C, the GPC remained almost constant at ∼0.10 nm/cycle, which suggests an ALD temperature window, whereas upon further increasing the temperature to 200 °C, the GPC considerably decreased to ∼0.04 nm/cycle. Thermodynamic analysis via density functional theory calculations showed that the self-saturation of TDMASn would occur on an NH2-terminated surface. Moreover, it also suggests that the condensation of a molecular precursor and the desorption of surface *NH2 moieties would occur at lower and higher temperatures outside the ALD window, respectively. Thanks to the characteristics of ALD, this process could be used to conformally and uniformly deposit SnNx onto an ultranarrow dual-trench Si structure (minimum width: 15 nm; aspect ratio: ∼6.3) with ∼100% step coverage. Several analysis tools such as transmission electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and secondary-ion mass spectrometry were used to characterize the film properties under different deposition conditions. XRD showed that a hexagonal SnN phase was obtained at a relatively low deposition temperature (100-150 °C), whereas cubic Sn3N4 was formed at a higher deposition temperature (175-200 °C). The stoichiometry of these thermally grown ALD-SnNx films (Sn-to-N ratio) deposited at 150 °C was determined to be ∼1:0.93 with negligible impurities. The optoelectronic properties of the SnNx films, such as the band gap, wavelength-dependent refractive index, extinction coefficient, carrier concentration, and mobility, were further evaluated via spectroscopic ellipsometry analysis. Finally, ALD-SnNx-coated Ni-foam (NF) and hollow carbon nanofibers were successfully used as free-standing electrodes in electrochemical supercapacitors and in Li-ion batteries, which showed a higher charge-storage time (about eight times greater than that of the uncoated NF) and a specific capacity of ∼520 mAh/g after 100 cycles at 0.1 A/g, respectively. This enhanced performance might be due to the uniform coverage of these substrates by ALD-SnNx, which ensures good electric contact and mechanical stability during electrochemical reactions.

Importance of precursor delivery mechanism for Tetra-kis-ethylmethylaminohafnium/water atomic layer deposition process

The present work investigates the importance of incorporating a boosting mechanism in an Atomic Layer Deposition (ALD) process for the delivery of a low vapour pressure precursor in the reaction chamber. Here we show that in the absence of the boosting mechanism, saturated growth was compromised and poor-quality films were obtained characterized by film non-uniformity and variable refractive index within the sample. We demonstrate that a boosting sequence of 0.5 s + 0.9 s with precursor bottle heating temperature of 120 °C was sufficient to produce good quality films showing saturated growth in our system. Furthermore, we demonstrate that for Tetra-kis-ethylmethylaminohafnium/water ALD process, the ALD window for hafnium oxide was found to be in the temperature range 300 °C–375 °C where the average growth per cycle and refractive index of the films deposited within the ALD window were found to be 1.16 Å/cycle and 2.00 respectively.