Atomic Layer Deposition Characteristics Research Articles

Plasma-enhanced atomic layer deposition of crystalline Ga2S3 thin films

Gallium (III) sulfide is a frontrunner for many energy storage and optoelectronic applications, which demand a deposition technique that offers a high level of control over thickness, composition, and conformality. Atomic layer deposition (ALD) is a potential technique in this regard. However, the state-of-the-art ALD processes for depositing Ga2S3 often lead to films that are amorphous and nonstoichiometric, and contain significant contaminations. Herein, we present a new plasma-enhanced atomic layer deposition (PE-ALD) process using the hexakis(dimethylamido)digallium precursor and H2S plasma coreactant to deposit high-quality Ga2S3 sulfide thin films and compare it to the thermal ALD process using the same reactants. While both cases exhibit typical ALD characteristics, substantial disparity is observed in the material properties. The PE-ALD process deposits crystalline Ga2S3 sulfide thin films at a temperature as low as 125 °C with a growth per cycle of 1.71 Å/cycle. Additionally, the PE-ALD process results in smooth and stoichiometric Ga2S3 films without any detectable carbon and oxygen contamination. Grazing incidence wide-angle x-ray scattering analysis indicates that the as-deposited Ga2S3 film crystallizes in a cubic structure with a preferred orientation along the [111] direction. The Ga2S3 film exhibits a transmittance of 70% and a bandgap of 3.2 eV with a direct transition.

Plasma-Enhanced Atomic Layer Deposition of Molybdenum Oxide Thin Films at Low Temperatures for Hydrogen Gas Sensing.

Molybdenum oxide thin films are very appealing for gas sensing applications due to their tunable material characteristics. Particularly, the growing demand for developing hydrogen sensors has triggered the exploration of functional materials such as molybdenum oxides (MoOx). Strategies to enhance the performance of MoOx-based gas sensors include nanostructured growth accompanied by precise control of composition and crystallinity. These features can be delivered by using atomic layer deposition (ALD) processing of thin films, where precursor chemistry plays an important role. Herein, we report a new plasma-enhanced ALD process for molybdenum oxide employing the molybdenum precursor [Mo(NtBu)2(tBu2DAD)] (DAD = diazadienyl) and oxygen plasma. Analysis of the film thickness reveals typical ALD characteristics such as linearity and surface saturation with a growth rate of 0.75 Å/cycle in a broad temperature window between 100 and 240 °C. While the films are amorphous at 100 °C, crystalline β-MoO3 is obtained at 240 °C. Compositional analysis reveals nearly stoichiometric and pure MoO3 films with oxygen vacancies present at the surface. Subsequently, hydrogen gas sensitivity of the molybdenum oxide thin films is demonstrated in a laboratory-scale chemiresistive hydrogen sensor setup at an operation temperature of 120 °C. Sensitivities of up to 18% are achieved for the film deposited at 240 °C, showing a strong correlation between crystallinity, oxygen vacancies at the surface, and hydrogen gas sensitivity.

Enhanced Resistive Switching and Synaptic Characteristics of ALD Deposited AlN-Based RRAM by Positive Soft Breakdown Process.

Nitride film played an essential role as an excellent diffusion barrier in the semiconductor field for several decades. In addition, interest in next-generation memories induced researchers' attention to nitride film as a new storage medium. A Pt/AlN/TaN device was investigated for resistive random-access memory (RRAM) application in this work. Resistive switching properties were examined in the AlN thin film formed by atomic layer deposition (ALD). The unique switching feature conducted under the positive voltage was investigated, while the typical bipolar switching was conducted under the application of negative voltage. Good retention and DC, and pulse endurances were achieved in both conditions and compared to the memory performances. Finally, the electronic behaviors based on the unique switching feature were analyzed through X-ray photoelectron spectroscopy (XPS) and the current-voltage (I-V) linear fitting model.

Preparation of tungsten-based thin films using a F-free W precursor and tert-butyl hydrazine via 2- and 3-step atomic layer deposition process

This article reports the preparation of tungsten metal (W) and other tungsten-based thin films using a F-free W metalorganic precursor tris(3-hexyne) mono-carbonyl tungsten [W(EtCCEt)3(CO)] (Et = C2H5), THMCT], tert-butyl hydrazine (TBH), and H2 plasma via 2- and 3-step atomic layer deposition (ALD) process. Density functional theory (DFT) calculations were performed to simulate the possible mechanisms of W4(EtCCEt)4(CO)4, as the model of chemisorbed THMCT on the growing surface, with TBH. The experimental findings agree well with the DFT results that the thermal ALD of THMCT and TBH could not deposit the pure W metal films. Instead, THMCT and TBH led to form an amorphous, tungsten oxycarbide, WOxCy (with a minor nitrogen content and a negligible amount of W metal phase), resulting in a very high resistivity of ∼80,000 μΩ-cm (at 300 °C). Nevertheless, the typical characteristics of ALD, such as the self-limiting growth, and a linear dependency of the film thickness with cycle variation, were obtained with a growth-per-cycle (GPC) of ∼0.4 Å. Post-annealing of the films in the H2 atmosphere resulted in a slight increase in the metallic phase formation with a significant drop in resistivity to ∼3500 μΩ-cm. However, the annealing also facilitated the formation of the tungsten oxide phase owing to the oxygen incorporated in the as-deposited films. Introducing an additional H2 plasma pulse step at the end of each ALD cycle (3-step ALD process) significantly altered the film composition and helped reduce the as-deposited film's resistivity drastically to ∼650 μΩ-cm. Also, the process results in the formation of tungsten carbide (WCx) as the predominant phase. Finally, the additional high-temperature-post-annealing of these 3-step ALD grown films resulted in extremely low resistivity of ∼200 μΩ-cm owing to the formation of body-centered-cubic (BCC) α-W. Thus, the envisaged path in this study to achieve W thin films also provides rooms to grow oxide or carbide dominant phase of W as studied in detail with the help of X-ray photoelectron spectroscopy

Understanding the active-site nature of vanadia-based catalysts for oxidative dehydrogenation of ethylbenzene with CO2 via atomic layer deposited VOx on γ-Al2O3

Supported vanadium oxides are widely used as active catalysts for a number of oxidation and oxidative dehydrogenation reactions, and the understanding the structure-function relationship is of great importance for developing more efficient vanadium oxide catalysts. In this work, atomic layer deposition (ALD) was utilized to disperse sub-monolayer VOx over a commercial γ-Al2O3 support. Characterization results indicate that highly dispersed VOx species with different structures were obtained by simply changing the number of ALD cycles. The vanadium oxides synthesized by performing 1 cycle of ALD were exclusively isolated monomeric VOx. With increasing the number of ALD cycles from 3 to 8, the polymeric VOx spices were formed, and the polymerization extent or domain size of VOx was increased. On the contrary, crystalline V2O5 besides polymeric VOx was found if the number of ALD cycles was extended to 12. Catalytic performances of ALD VOx/γ-Al2O3 were evaluated for the oxidative dehydrogenation of ethylbenzene with CO2 (CO2-ODEB), and the isolated monomeric VOx species were found to be more active and more stable than the polymeric VOx species and crystalline V2O5. By correlating the specific activity and the structural characteristics of ALD VOx/γ-Al2O3 catalysts, the VOAl bonds were concluded as the key active sites for CO2-ODEB.

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.

Atomic layer deposition of Ta-doped SnO2 films with enhanced dopant distribution for thermally stable capacitor electrode applications

Atomic layer deposition (ALD) on Ta-doped SnO2 thin films is proposed as a methodology for the fabrication of capacitor electrodes, for application in dynamic random-access memories (DRAMs). In ALD of doped materials, dopant concentration gradients inevitably occur due to the cyclic process-based characteristics of ALD. In this study, the dopant distribution improves drastically by the decrease in the growth per cycle of TaOx ALD. The modified ALD recipe exploits the low reactivity between Ta and Sn precursors to facilitate a reduction in the growth per cycle. The Ta-doped SnO2 films grown based on this modified ALD recipe exhibit improved crystallinity and conductivity. The ALD process yields excellent conformality of the Ta-doped SnO2 film over a hole structure with a high aspect ratio of ~10, both in terms of physical thickness and composition. Additionally, the Ta-doped SnO2 films serve as a template for the overgrowing dielectric TiO2 film, which induces the formation of a high-temperature phase with a high dielectric constant, rutile TiO2, and exhibit excellent thermal stability even after annealing at 400 °C in forming gas atmosphere. These findings demonstrate that the proposed methodology for the growth of Ta-doped SnO2 can facilitate the fabrication of capacitor electrodes for application in DRAMs.

Atomic layer deposition of WNx thin films using a F-free tungsten metal-organic precursor and NH3 plasma as a Cu-diffusion barrier

Tungsten nitride (WNx) thin films were deposited on SiO2 substrates by atomic layer deposition (ALD) using a fluorine- free tungsten metal-organic precursor of tris(3-hexyne) tungsten carbonyl, W(CO)(CH3CH2C ≡ CCH2CH3)3 and NH3 plasma as a reactant at a deposition temperature of 250 °C. Important ALD characteristics, such as self-limiting growth and linear dependency of the film growth on the number of ALD cycles, were obtained with a growth rate of 0.045 nm/cycle. The minimum film resistivity of around ~2800 μΩcm (thickness: ~ 13.3 nm) was stable after 3 days air-exposure, indicating the high stability of these WNx films. Rutherford backscattering spectrometry showed that the N-rich WNx thin films (N/W ratio: ~ 1.56) were deposited with negligible impurities of C and O. Both X-ray diffractometry and transmission electron microscopy analysis showed that ALD-WNx films formed a polycrystalline cubic WN phase with an average grainsize of ~ 6 nm. From scanning Kelvin probe analysis, its work function was determined as 4.79 eV. Detail investigations were carried out after post-annealing of the as-deposited films and formation of metallic-W with significantly reduced sheet resistance was observed upon annealing at and beyond 700 °C. Finally, the ultrathin (~5 nm) ALD-grown WNx film effectively prevented diffusion of Cu even up to 550 °C, promising it as an efficient diffusion barrier material for the Cu interconnect.

Redox Layer Deposition of Thin Films of MnO2 on Nanostructured Substrates from Aqueous Solutions

In this work, we report a new method for depositing thin films of MnO2 on planar and complex nanostructured surfaces, with high precision and conformality. The method is based on repeating cycles of adsorption of an unsaturated alcohol on a surface, followed by its oxidation with aqueous KMnO4 and formation of thin, solid MnO2. The amount of manganese oxide formed in each cycle is limited by the quantity of the adsorbed alcohol; thus, the growth exhibits the self-limiting characteristics of atomic layer deposition (ALD). Contrary to the typical ALD, however, the new redox layer deposition is performed in air, at room temperature, using common chemicals and simple laboratory glassware, which greatly reduces its cost and complexity. We also demonstrate application of the method for the fabrication of a nanostructured MnO2/Ni electrode, which was not possible with thermal ALD because of the rapid decomposition of the gaseous precursor on the high surface-area substrate. Thanks to its simplicity, the conformal deposition of MnO2 can be easily upscaled and thus exploited for its numerous (electro)chemical applications.

Enhanced Electrochemical Stability of TiO2-Protected, Al-doped ZnO Transparent Conducting Oxide Synthesized by Atomic Layer Deposition.

Transparent, conductive coatings on porous, three-dimensional materials are often used as the current collector for photoelectrode designs in photoelectrochemical applications. These structures allow for improved light trapping and absorption in chemically synthesized, photoactive overlayers while minimizing parasitic absorption in the current collecting layer. Atomic layer deposition (ALD) is particularly useful for fabricating transparent conducting oxides (TCOs) like Sn-doped In2O3 (ITO) and Al-doped ZnO (AZO) for structured materials because the deposition is specific to exposed surfaces. Unlike line-of-sight deposition methods (evaporation, spray pyrolysis, sputtering), ALD can access the entire complex interface to make a conformal transparent conductive layer. While ITO and AZO can be grown by ALD, they are intrinsically soluble in the acidic and basic environments common for electrochemical applications like water splitting. To take advantage of the unique characteristics of ALD in these applications, it is important to develop strategies for fabricating TCO layers with enhanced chemical stability. Ultrathin coatings of stable materials can be used to protect otherwise unstable electrochemical interfaces while maintaining the desired function. Here, we describe experiments to characterize the chemical and electrochemical stability of ALD-deposited AZO TCO thin films protected by a 10 nm TiO2 overlayer. The addition of a TiO2 protection layer is demonstrated to improve the chemical stability of AZO by orders of magnitude compared to unprotected, yet otherwise identically prepared, AZO films. The electrochemical stability is enhanced accordingly in both acidic and basic environments. We demonstrate that TiO2-protected AZO can be used as a TCO for both the cathodic hydrogen evolution (HER) and anodic water oxidation (OER) half-reactions of electrochemical water splitting in base and for HER in acid when the appropriate electrocatalysts are added. As a result, we show that ALD can be used to synthesize a chemically stable TCO heterostructure, expanding the range of materials and electrochemical environments available for building complex photoelectrode architectures.

Plasma-Enhanced Atomic Layer Deposition of Silver Using Ag(fod)(PEt3) and NH3-Plasma

A plasma-enhanced atomic layer deposition (ALD) process using the Ag(fod)(PEt3) precursor [(triethylphosphine)(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate)silver(I)] in combination with NH3-plasma is reported. The steady growth rate of the reported process (0.24 ± 0.03 nm/cycle) was found to be 6 times larger than that of the previously reported Ag ALD process based on the same precursor in combination with H2-plasma (0.04 ± 0.02 nm/cycle). The ALD characteristics of the H2-plasma and NH3-plasma processes were verified. The deposited Ag films were polycrystalline face-centered cubic Ag for both processes. The film morphology was investigated by ex situ scanning electron microscopy and grazing-incidence small-angle X-ray scattering, and it was found that films grown with the NH3-plasma process exhibit a much higher particle areal density and smaller particle sizes on oxide substrates compared to those deposited using the H2-plasma process. This control over morphology of the deposited Ag is important for applications in catalysis and plasmonics. While films grown with the H2-plasma process had oxygen impurities (∼9 atom %) in the bulk, the main impurity for the NH3-plasma process was nitrogen (∼7 atom %). In situ Fourier transform infrared spectroscopy experiments suggest that these nitrogen impurities are derived from NHx surface groups generated during the NH3-plasma, which interact with the precursor molecules during the precursor pulse. We propose that the reaction of these surface groups with the precursor leads to additional deposition of Ag atoms during the precursor pulse compared to the H2-plasma process, which explains the enhanced growth rate of the NH3-plasma process.

Chemical Processes Involved in Atomic Layer Deposition of Gallium Sulfide: Insights from Theory

Growth characteristics of atomic layer deposition (ALD) of gallium sulfide (GaxS) from tris(dimethylamino)gallium (Ga(NMe2)3) and hydrogen sulfide (H2S) have been investigated by density functional theory. The steady-state film growth during one ALD cycle was modeled by studying the energetics of a large set of reactions taking place on a surface described as a SH-terminated gallium sulfide (Ga2S3) cluster. The opportunity of using gas-phase cluster calculations to compute entropic contributions is discussed. Detailed reaction mechanisms are provided, along with free energy profiles and a large reaction network emerges. It confirms a ligand loss/exchange mechanism, and various aspects of the growth are explored (fate of the precursor and co-reactant, self-saturation of the surface, crawling and cooperative effects, role of the amido ligand, of the impurities, etc.) and confronted to experimental observations. All the key reaction steps are facile and thermodynamically favorable, while undesired side react...

Atomic layer deposited nanocrystalline tungsten carbides thin films as a metal gate and diffusion barrier for Cu metallization

Tungsten carbides (WCx) thin films were deposited on thermally grown SiO2 substrates by atomic layer deposition (ALD) using a fluorine- and nitrogen-free W metallorganic precursor, tungsten tris(3-hexyne) carbonyl [W(CO)(CH3CH2C ≡ CCH2CH3)3], and N2 + H2 plasma as the reactant at deposition temperatures between 150 and 350 °C. The present ALD-WCx system showed an ALD temperature window between 200 and 250 °C, where the growth rate was independent of the deposition temperature. Typical ALD characteristics, such as self-limited film growth and a linear dependency of the film grown on the number of ALD cycles, were observed, with a growth rate of 0.052 nm/cycle at a deposition temperature of 250 °C. The ALD-WCx films formed a nanocrystalline structure with grains, ∼2 nm in size, which consisted of hexagonal W2C, WC, and nonstoichiometric cubic β-WC1−x phase. Under typical deposition conditions at 250 °C, an ALD-WCx film with a resistivity of ∼510 μΩ cm was deposited and the resistivity of the ALD-WCx film could be reduced even further to ∼285 μΩ cm by further optimizing the reactant pulsing conditions, such as the plasma power. The step coverage of ALD-WCx film was ∼80% on very small sized and dual trenched structures (bottom width of 15 nm and aspect ratio of ∼6.3). From ultraviolet photoelectron spectroscopy, the work function of the ALD-WCx film was determined to be 4.63 eV. Finally, the ultrathin (∼5 nm) ALD-WCx film blocked the diffusion of Cu, even up to 600 °C, which makes it a promising a diffusion barrier material for Cu interconnects.

Highly-conformal nanocrystalline molybdenum nitride thin films by atomic layer deposition as a diffusion barrier against Cu

Molybdenum nitride (Mo2N) thin films were grown by atomic layer deposition (ALD) using a sequential supply of a newly synthesized Mo metalorgranic precursor, Mo(NtBu)2(StBu)2, and H2 plasma at a substrate temperature of 300 °C. A newly proposed ALD system exhibited typical ALD characteristics, such as a self-limited film growth and a linear dependency of the film thickness on the number of ALD cycles, and showed a growth rate of 0.028 nm/cycle on a thermally grown SiO2 substrate. Such the ideal ALD growth characteristics enabled excellent step coverage of ∼80% for the ALD-grown Mo2N film onto nano-trenches with a width of 25 nm and an aspect ratio ∼4.5. The optimized film had a resistivity as low as ∼350 μΩ-cm. X-ray diffraction, Rutherford backscattering spectrometry, and X-ray photoelectron spectroscopy analyses confirmed that formation of N-rich cubic Mo2N (N/Mo = ∼0.7) phase with carbon and sulfur impurities of 2.6 and 7.4 at.%, respectively. Plan-view transmission electron microscopy analysis showed that the film formed a nanocrystalline microstructure with 5–8-nm-sized grains embedded in an amorphous matrix. An ultrathin (only ∼4 nm-thick) ALD-grown Mo2N film effectively prevented diffusion of Cu into Si after annealing at a temperature even up to 650 °C.

Nucleation and Growth of the HfO2 Dielectric Layer for Graphene-Based Devices

We investigated nucleation and growth characteristics of atomic layer deposition (ALD) HfO2 on exfoliated and chemical vapor deposition (CVD) graphene by using two Hf precursors, tetrakis(dimethylamino)hafnium (TDMAH) and hafnium tetrachloride (HfCl4). Experimental results and theoretical calculations indicate that HfO2 nucleation is more favorable on CVD graphene than on exfoliated graphene due to the existence of defect sites. Also, the TDMAH precursor showed much more unfavorable nucleation and growth than HfCl4 due to different initial adsorption mechanisms, affecting lower leakage currents and breakdown electric field. ALD growth characteristics of HfO2 will be fundamentally and practically significant for realizing the fabrication of graphene-based electronic devices.

Study on Effect of Proton Irradiation Energy in AlGaN/GaN Metal-Oxide Semiconductor High Electron Mobility Transistors

AlGaN/GaN high electron mobility transistors (HEMTs) showed its promising features in high power and high frequency applications such as inverter units in hybrid electric vehicles, advanced radar systems, and satellite-based communication networks with its high density of sheet carrier concentration, high electron mobility, and radiation hardness. However, the high gate leakage and current collapse limits the reliability and performance of the HEMTs. In the other hand, using oxide as gate dielectric solves the problems at the same time not degrading the device performances. In this paper, we investigated the effect of the proton energy dependency on dc characteristics of atomic layer deposition (ALD) deposited Al2O3 gate dielectric AlGaN/GaN MOS-HEMTs. AlGaN/GaN MOS-HEMTs were irradiation with fixed proton dose of 5 × 1015 cm-2 at 5MeV, 10MeV, and 15MeV. The MOS-HEMTs’ dc characteristics were compared before and after the irradiation to assess the damage done by irradiation. AlGaN/GaN epilayer were grown on sapphire substrate by metal-organic chemical vapor deposition (MOCVD), consisting of 5 μm GaN buffer, 21 nm of undoped Al0.24Ga0.76N, and a 5 nm undoped GaN cap. On-wafer Hall measurement was used to measure sheet resistance, sheet carrier concentration, and mobility of 479 Ω/□, 9.55 × 1012 cm-2, and 1363 cm2/V·s respectively. Mesa isolation process was achieved by Unaxis Shuttlelock Reactive Ion Etcher with Inductively Coupled Plasma Module (ICP) with Cl2/Ar plasma. Consisting of Ti/Al/Ni/Au (25 nm/125 nm/45 nm/100 nm), 5 μm distance of source to drain Ohmic metallization was achieved by lift-off process of electron-beam evaporator deposited Ohmic metal. Rapid thermal annealing at 850ºC with N2 ambient for 45 seconds was followed by Ohmic metallization. A 10 nm Al2O3 layer was deposited by ALD at 300ºC. Ni/Au (20nm/80nm) gate metal with 100 μm width and 1 μm length was deposited by liftoff of e-beam evaporator. After fabricating MOS-HEMT, proton irradiation was projected at the Korean Institute of Radiological & Medical Sciences (KIRAMS) using a MC 50 (Scanditronix) cyclotron with proton fluence of 5 × 1015 cm-2 at 5MeV. MOS-HEMT’s dc characteristics were measured by 4156 HP parameter analyzer. Transmission line measurement (TLM) was used to measure sheet resistance (RS), transfer resistance (RT), and contact resistance (RC) before and after proton irradiation. Stopping and range of ions in matter simulations (SRIMS) was used to simulate the penetration depth of the protons into AlGaN/GaN MOS-HEMTs at different proton energies. Figure 1 shows the effect of 5 × 1015 cm-2 proton irradiation at 10MeV on drain I-V characteristics before and after. The saturation current, IDSS, was reduced by 68.3% and mobility, which was calculated from linear region of drain I-V curve using charge control model, was reduced by 69.3%. These reductions were due to the displacement damage induced by ion bombardment from proton irradiation. Table 1 shows the summary of MOS-HEMTs device degradation in IDSS, transconductance, threshold voltage shift, mobility, and sheet carrier concentration. In conclusion, irradiation-induced damage causes the reductions of carrier mobility and carrier concentration. The severe degradation in lower irradiation energy is observed due to the more acceptor type defects generated near the 2 dimensional electron gas channel. Figure 1

Investigating atomic layer deposition characteristics in multi-outlet viscous flow reactors through reactor scale simulations

In order to minimize the operational time of atomic layer deposition (ALD) process, flow transports and film depositions are investigated in multi-outlet viscous flow reactors through reactor scale simulations. The simulation process is performed on depositions of Al2O3 films using trimethylaluminum and ozone as the precursors, and inert argon as the purge gas. The chemistry mechanism used includes both gas-phase and surface reactions. Simulations are performed at a fixed operating pressure of 10Torr (1330Pa) and at two substrate temperatures of 250°C and 300°C, respectively. Flows inside the reactors are following the continuum approach; as a result, the Navier–Stokes, energy and species transport equations can be used to simulate transient, laminar and multi-component reacting flows. Based on the chemistry mechanism adopted in this study, the amount of oxygen atoms produced from the ozone decomposition is found to be the major reason for discrepancies in oxidation times and deposition rates at different ALD processes. A reactor with fewer outlets minimizes the ALD operational times by reducing both oxidation time and second purge time. In addition, higher deposition rates at a shorter time are obtained by using a reactor with fewer outlets. However, assigning a long enough time for the ozone exposure results in independency of ALD characteristics from the number of outlets such that the growth rates of around 3.78angstrom/cycle and 4.52angstrom/cycle are obtained for the substrate temperatures of 250°C and 300°C, respectively.

Highly Conformal Amorphous W–Si–N Thin Films by Plasma-Enhanced Atomic Layer Deposition as a Diffusion Barrier for Cu Metallization

Ternary and amorphous tungsten silicon nitride (W–Si–N) thin films were grown by atomic layer deposition (ALD) using a sequential supply of a new fluorine-free, silylamide-based W metallorganic precursor, bis(tert-butylimido)bis(bis(trimethylsilylamido))tungsten(VI) [W(NtBu)2{N(SiMe3)2}2], and H2 plasma at a substrate temperature of 300 °C. Here, W(NtBu)2{N(SiMe3)2}2 was prepared through a metathesis reaction of W(NtBu)2Cl2(py)2 (py = pyridine) with 2 equiv of LiN(SiMe3)2 [Li(btsa)]. The newly proposed ALD system exhibited typical ALD characteristics, such as self-limited film growth and linear dependency of the film growth on the number of ALD cycles, and showed a high growth rate of 0.072 nm/cycle on a thermally grown SiO2 substrate with a nearly zero incubation cycle. Such ideal ALD growth characteristics enabled excellent step coverage of ALD-grown W–Si–N film, ∼100%, onto nanotrenches with a width of 25 nm and an aspect ratio ∼4.5. Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy analysis confirmed that the incorporated Si and W were mostly bonded to N, as in Si–N and W–N chemical bonds. The film kept its amorphous nature until annealing at 800 °C, and crystallization happened at local areas after annealing at a very high temperature of 900 °C. An ultrathin (only ∼4 nm thick) ALD-grown W–Si–N film effectively prevented diffusion of Cu into Si after annealing at a temperature up to 600 °C.

Flash-Enhanced Atomic Layer Deposition: Basics, Opportunities, Review, and Principal Studies on the Flash-Enhanced Growth of Thin Films

Within this work, flash lamp annealing (FLA) is utilized to thermally enhance the film growth in atomic layer deposition (ALD). First, the basic principles of this flash-enhanced ALD (FEALD) are presented in detail, the technology is reviewed and classified. Thereafter, results of our studies on the FEALD of aluminum-based and ruthenium thin films are presented. These depositions were realized by periodically flashing on a substrate during the precursor exposure. In both cases, the film growth is induced by the flash heating and the processes exhibit typical ALD characteristics such as layer-by-layer growth and growth rates smaller than one Å/cycle. The obtained relations between process parameters and film growth parameters are discussed with the main focus on the impact of the FLA-caused temperature profile on the film growth. Similar, substrate-dependent growth rates are attributed to the different optical characteristics of the applied substrates. Regarding the ruthenium deposition, a single-source process was realized. It was also successfully applied to significantly enhance the nucleation behavior in order to overcome substrate-inhibited film growth. Besides, this work addresses technical challenges for the practical realization of this film deposition method and demonstrates the potential of this technology to extend the capabilities of thermal ALD.

Flash-Lamp-Enhanced Atomic Layer Deposition of Thin Films

Within this work flash lamp annealing (FLA) is utilized to thermally enhance the film growth in atomic layer deposition (ALD). First, the basic principles of flash-lamp-enhanced ALD (FEALD) are presented in detail, the technology is reviewed and classified. Thereafter, results of our studies on the FEALD of aluminum- and ruthenium-based thin films are presented. These depositions were realized by periodically flashing on a substrate during the precursor exposure. It is shown that the film growth is induced by the flash heating and that the processes exhibit typical ALD characteristics. The obtained relations between flash parameters and film growth parameters are discussed with the main focus on the impact of the FLA-caused temperature profile on the film growth. Besides, this work addresses technical challenges for the practical realization of this method and demonstrates the potential of this technology to extend the capabilities of thermal ALD.