A Field-Driven Growth Model for Uniform Thin-Film Growth.

Iridium (Ir) thin films have been extensively investigated for a variety of applications. Ir is a potential optical material for Fresnel zone X-ray microchannel plates, and inductive grid filters. It is also a noble metal making it well suited to corrosion resistance in harsh environments Atomic Layer Deposition (ALD) is considered a special case of chemical vapor deposition (CVD) in that two different chemical precursor materials are alternately introduced into a vacuum chamber where a chemical reaction occurs on the surface of the substrate. This method of thin film growth is self-limiting and conformal and consequently results in precise layer thickness control, stoichiometry, composition, and uniformity across a large surface area. Advantages that are unique to ALD include the ability to grow conformal thin films across complex geometries, and the relatively low temperatures required to achieve film growth. In this work, iridium metal films were synthesized on silicon (Si) and Monel K-500 alloy substrates by ALD using Iridium (III) acetylacetonate known as Ir(acac)3 or [CH3COCH=C(O-)CH3]3 Ir as precursor 1, and industrial grade O2 as oxidizing reactant. The solid Ir precursor was heated to 150 °C, and the substrate temperature was varied to establish an optimum growth window. The lowest temperature in which Ir growth was found is 200 °C, and the thin film growth rate increased as a function of temperature up to 250 °C. Higher temperatures have not yet been attempted due to equipment constraints. The Monel K-500 steel alloy flat discs were cut from commercially available Monel K-500 bars of ~1 inch diameter. In this study we report on the successful synthesis of Ir films on Si and Monel K-500 substrates. Detailed characterization has been performed using X-ray diffraction (XRD) techniques, atomic force microscopy (AFM), and field emission scanning electron microscopy (FE-SEM) of samples which have been notched with focused ion beam (FIB) techniques for cross-sectional film thickness measurements as revealed in Figure 1. The polycrystalline ALD Iridium film exhibited good chemisorption and adhesion to native oxide covered Si substrates, with hydroxyl surface termination. However even with the absence of a SiO2 surface film, the ALD synthesis of Iridium metal films worked equally well on the Monel K-500 steel alloy flat disc substrates and yielded excellent surface coverage.

CuInS2 (CIS) thin films are prepared by the successive ionic layer adsorption and reaction method (SILAR) by single cationic route under two different conditions (without stirring and with stirring). The effect of stirring on the structural, optical, compositional and morphological properties of the prepared Cu-rich CuInS2 thin films has been studied and reported in this paper. Full Text: PDF References M.Krunks, A.Mere, A.Katerski, V.Mikli and J.Krustok, "Characterization of sprayed CuInS2 films annealed in hydrogen sulfide atmosphere", Thin Solid Films 511-512, 434 (2006).CrossRef S.K.Kim, W.J.Jeong, G.C.Park, Y.G.Back, Y.G.Jeong and Y.T.Yoo, "Heat-treatment effect of chalcopyrite copper indium disulphide thin film growth", Synthetic Metals 71, 1747 (1995).CrossRef Roland Scheer, Progress in photovoltaics: Research and Applications, "Open questions after 20 years of CuInS2 research", (2012).CrossRef M.Krunks, O.Kijatkina, H.Renace, I.Oja, V.Mikli and A.Mere, "Composition of CuInS2 thin films prepared by spray pyrolysis", Thin Solid Films 403-404, 71 (2002).CrossRef Y.B.He, T.Kramer, I.Osterreicher, A.polity, R.Gregor, W. Krieg seis, D.Hasselkamp and B.K.Meyer, "Highly (112)-Oriented CuInS2 Thin Films Deposited by a One-Stage RF Reactive Sputtering Process", Jpn.J.Appl.Phys. 41, L484 (2002).CrossRef J.Qiu, Z.Jin, J.Qian, Y.Shi and W.Wu, "ILGAR CuInS2 films from various preparation conditions", Mater. Lett. 59, 2735 (2005).CrossRef N.Suriyanarayanan and C.Mahendran, "EDAX, SEM, Photoluminescence and Electrical properties of Zn- doped polycrystalline CuInS2 Thin films by spray pyrolysis", Archives of Physics Research 3 (1), 54 (2012).DirectLink Y.Pena, S.Lugo, M.C.Rodriguez, A.Vazquez, I.Gomez and P.Elizo nodo, "CuInS2 thin films obtained through the annealing of chemically deposited In2S3?CuS thin films", Appl.Surf. Sci. 257, 2193 (2011).CrossRef A.B.Mandale, S.D.Sathaye and K.R.Patil, "Preparation of Q-copper indium sulfide thin films by liquid?liquid interface reaction technique (LLIRT)", Mater. Lett. 55, 30 (2002).CrossRef M.Ben Rabeh, N.Chaglabou and M.Kanzari, "Effect of Antimony Incorporation in CuInS2 Thin Films", Chalcogenide Lett. 6 (4),155 (2009).CrossRef Y.B.He, A.Polity, R.Gregor, D.Pfisterer, I.Osterreicher, D.Hasse lkamp and B.K.Meyer, "Characterization of RF reactively sputtered Cu?In?S thin films", Physics B. 308-310, 1074 (2001).CrossRef K.Zeaiter, Y.Llinares and C.Llinares, "Structural and photoluminescence study of the quaternary alloys system CuIn(SxSe1?x)2", Sol. Energy Mater. Sol. Cells 61, 313 (2000).CrossRef A.Antony, A.S.Asha, R.Yoosuf, R.Manoj and M.K.Jayaraj, "Growth of CuInS2 thin films by sulphurisation of Cu?In alloys", Sol. Energy Mater. Sol. Cells 81, 407 (2004)CrossRef Y.Shi, Z.Jin, C.Li, H.An and J.Qiu, "Effect of [Cu]/[In] ratio on properties of CuInS2 thin films prepared by successive ionic layer absorption and reaction method", Appl. Surf. Sci. 252, 3737 (2006).CrossRef S.J.Roh, R.SMane, H.Pathan, O.S.Joo and S.H.Han, "Rapid growth of nanocrystalline CuInS2 thin films in alkaline medium at room temperature", Appl. Surf. Sci. 252, 1981 (2005).CrossRef Gray Hodes, Chemical Solution Deposition of Semiconductor Films (Marcel Dekker, Inc, pp-131).DirectLink R.P.Wijesundera and W.Siripala, "Preparation of CuInS2 thin films by electrodeposition and sulphurisation for applications in solar cells", Sol. Energy Mater. Sol. Cells 81, 147 (2004).CrossRef C.Guillen, J.Herrero, M.T.Gutierrez and F.Briones, "Structure, morphology and optical properties of CuInS2 thin films prepared by modulated flux deposition", Thin solid films 480- 481, 19 (2005). DirectLink P.Guha, S.Gorai, D.Ganguli and S.Chanudhuri, "Ammonia-mediated wet chemical synthesis of CuInS2"Mater. Lett. 57, 1786 (2003).CrossRef Y.B.He. T.Kramer, I.Osterreicher, A.Polity, B.K.Meyer and M.Hardt, "Post-growth treatment effects on properties of CuInS2 thin films deposited by RF reactive sputtering", Semicond. Sci.Technol. 20, 685 (2005).CrossRef S.Aksay and B.Altiokka, "Effect of substrate temperature on some of the optical parameters of CuInS2 films", Physica Status Solidi (c) 4, 585-588, No.2 (2007)CrossRef N.M.Ravindra, Preethi Ganapathy, Jinsoo Choi, "Energy gap?refractive index relations in semiconductors ? An overview", Infrared Physics and Technology, 50, 1 21 (2007)CrossRef

Due to various applications in electronic and optical fields, considerable efforts have been made to develop ZnO based semiconducting materials. ZnO has a wide and direct band gap of 3.37 eV, large exciton binding energy (60 meV), high mechanical and thermal stabilities, and good electrical conductivity. Therefore, ZnO thin films are intensively investigated and applied in solar cells, piezoelectrical devices, gas and biological sensors, catalysts, and high-efficiency short-wavelength optoelectronic nanodevices. To further enhance the properties of ZnO, researchers have been synthesizing ZnO films doped with aluminum or indium. Al doped ZnO (AZO) thin films have been highly developed featuring non-toxicity, low material cost, good thermal stability, high optical transmittance, and good electrical conductivity. [1, 2, 3] Many techniques have been used to deposit AZO thin films currently, such as sol gel processing, magnetron sputtering, pulsed laser deposition (PLD), chemical vapor deposition (CVD), and atomic layer deposition (ALD). Among these film deposition methods, ALD has been extensively investigated for the deposition of thin films of metals, alloys, semiconductors, and oxides. Compared with other techniques, ALD is considered as a novel technique for the deposition of AZO films due to its characteristic feature of self-limiting surface saturating reactions in each ALD cycle. ALD technology consequently and accurately controls the layer thickness with unprecedented atomic level precision, as well as the stoichiometry, composition, uniformity of large areas and maintains excellent conformity over complex surface nanostructures. The other advantage of ALD technology is to introduce each ALD chemical precursor sequentially separated by time to react on the surface of the structure. The concentration of dopant in the ZnO films can be precisely controlled by the number of ALD cycles, so that the physical properties of AZO films, such as carrier density and conductivity, can be adjusted to meet the requirements of different applications. In this study, a Savannah 100 cross-flow thermal ALD reactor was used for the deposition of Al doped ZnO thin films. The precursors of aluminium, zinc and oxygen used in the ALD process for the synthesis of Al doped ZnO thin films were trimethylaluminium (TMA: Al2(CH3)6), diethylzinc (DEZ: (C2H5)2Zn) and DI water. The growth temperature of AZO thin films was maintained at 250 oC. The flow rate of N2, used as a carrier gas, was accurately controlled at 20 sccm. In order to deposit ALD AZO films with various percentages of aluminium, TMA cycles were introduced once in every 30 pulses of DEZ and H2O injection. After deposition, AZO films were annealed in air at 500 oC, 600 oC, and 700 oC for 30 min, respectively. X-ray diffraction (XRD) was performed to characterize the crystal structure of ALD ZnO and AZO films. Field emission scanning electron microscopy (FE-SEM) was used to inspect the morphology of AZO films before and after annealing. The surface roughness was analyzed by atomic force microscopy (AFM). The compositions of AZO thin films were analyzed by energy dispersive X-ray spectroscopy (EDS). The sheet resistivity of AZO films was determined by using four-point probe measurements. Raman spectroscopy and photoluminescence (PL) were used to investigate the properties and detect structures of ALD AZO films. The band gaps of AZO films prepared by the ALD process were analyzed from PL spectroscopy results. The materials property and defect structure of ALD AZO films were investigated by Raman spectroscopy.

Elastomeric primer and adhesive systemSection:ChooseTop of pageElastomeric primer and ad... <<Atomic layer deposition p...Cold cathode vacuum trans...X-ray fluorescence systemPrecision UV mirrorsSolder paste for fine-fea...Process for diamond-like ...Liquid transfer pumpNew literatureEllipsometer for thin-fil...Specialized vacuum gauges...CITING ARTICLES Master Bond X21Med is a single-component elastomeric compound that passes ISO 10993-5 tests for cytotoxicity. It was developed as a primer to promote adhesion between polyolefins and other surfaces such as metals, ceramics, composites, and other kinds of plastics, but it can also bond two polyolefin materials. Easy to use, X21Med has a low viscosity of less than 250 cps. It cures at ambient temperatures; with heat, it cures more rapidly. It is serviceable from −51 °C to 93 °C. As a primer, X21Med should be applied in a thin layer to the surface and then the solvent allowed to evaporate. 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Master Bond Inc, 154 Hobart St, Hackensack, NJ 07601, www.masterbond.com Atomic layer deposition plasma-processing systemSection:ChooseTop of pageElastomeric primer and ad...Atomic layer deposition p... <<Cold cathode vacuum trans...X-ray fluorescence systemPrecision UV mirrorsSolder paste for fine-fea...Process for diamond-like ...Liquid transfer pumpNew literatureEllipsometer for thin-fil...Specialized vacuum gauges...CITING ARTICLES Oxford Instruments has announced the novel FlexAL-2D system for atomic layer deposition (ALD) of 2D transition-metal dichalcogenides for nanodevice applications. The FlexAL-2D system implements plasma-enhanced ALD to synthesize layers of 2D molybdenum disulfide films with tunable morphologies—namely, in-plane and vertically standing nanoscale architectures on CMOS-compatible silicon dioxide and silicon substrates. 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Oxford Instruments plc, 300 Baker Ave, Ste 150, Concord, MA 01742, www.oxford-instruments.com Cold cathode vacuum transducerSection:ChooseTop of pageElastomeric primer and ad...Atomic layer deposition p...Cold cathode vacuum trans... <<X-ray fluorescence systemPrecision UV mirrorsSolder paste for fine-fea...Process for diamond-like ...Liquid transfer pumpNew literatureEllipsometer for thin-fil...Specialized vacuum gauges...CITING ARTICLES The MKS Granville-Phillips 523 wide-range cold cathode vacuum transducer is suitable for applications that require an economical cold cathode with limited accuracy for simple, repeatable pressure measurement. It combines diverse materials and two types of discharge. The 523 covers a wide pressure range from 10−7 torr to atmosphere without the use of a conventional heat-loss Pirani sensor. A high-pressure discharge cell makes a second vacuum sensor unnecessary. The device can be mounted in any orientation, has a simple analog output, and complies with Restriction of Hazardous Substances and CE standards. Applications include analytical equipment such as mass spectrometers, scanning electron microscopes, industrial coating systems, and general vacuum-based pressure measurement apparatus. MKS Instruments Inc, 2 Tech Dr, Ste 201, Andover, MA 01810, www.mksinst.com X-ray fluorescence systemSection:ChooseTop of pageElastomeric primer and ad...Atomic layer deposition p...Cold cathode vacuum trans...X-ray fluorescence system <<Precision UV mirrorsSolder paste for fine-fea...Process for diamond-like ...Liquid transfer pumpNew literatureEllipsometer for thin-fil...Specialized vacuum gauges...CITING ARTICLES Bruker has announced its S8 Tiger Series 2 wavelength dispersive x-ray fluorescence (WDXRF) system for advanced quantitative elemental analysis in academic and industrial research and materials quality control. Measurement times are reduced, sample throughput is increased, and time to result is improved, typically by 25% over the previous model. The S8 Tiger Series 2 features XRF2 small spot mapping for detailed maps of elemental distributions in materials. With a 300 µm spot size, XRF2 offers the highest spatial resolution available in WDXRF, according to Bruker. The system introduces the company’s novel HighSense technology, which offers a wide linear dynamic range to enable higher precision levels for process and quality control. The x-ray optics improves sensitivity and spectral resolution to benefit a wide range of applications, including recognition of foreign particles and analysis of material properties in metals, minerals, semiconductors, glass, ceramics, and nanotechnology. Bruker AXS GmbH, Oestliche Rheinbrueckenstr 49, 76187 Karlsruhe, Germany, www.bruker.com Precision UV mirrorsSection:ChooseTop of pageElastomeric primer and ad...Atomic layer deposition p...Cold cathode vacuum trans...X-ray fluorescence systemPrecision UV mirrors <<Solder paste for fine-fea...Process for diamond-like ...Liquid transfer pumpNew literatureEllipsometer for thin-fil...Specialized vacuum gauges...CITING ARTICLES Edmund Optics offers its TechSpec precision UV mirrors in deep-UV (DUV) and new vacuum-UV (VUV) enhanced coatings. They are suitable for use in numerous optical setups to reflect UV light, including fluorescence microscopy and spectrometry, and for various commercially available light sources. The mirrors with DUV coating offer excellent reflection from 190 nm to long-wave IR (LWIR), and the VUV-coated mirrors provide optimized reflection from 120 nm to LWIR. 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Edmund Optics Inc, 101 E Gloucester Pike, Barrington, NJ 08007-1380, www.edmundoptics.com Solder paste for fine-feature printingSection:ChooseTop of pageElastomeric primer and ad...Atomic layer deposition p...Cold cathode vacuum trans...X-ray fluorescence systemPrecision UV mirrorsSolder paste for fine-fea... <<Process for diamond-like ...Liquid transfer pumpNew literatureEllipsometer for thin-fil...Specialized vacuum gauges...CITING ARTICLES Indium Corp has developed an air and nitrogen reflow, no-clean, lead-free solder paste to meet the fine-feature printing requirements of mobile manufacturers. The Indium11.8HF-SPR (T5-MC) paste is formulated for use with type 5 powder. It delivers high-stencil print-transfer efficiency on a broad range of processes while maintaining high reflow performance, and it is halogen free, per the International Electrochemical Commission’s standard 61249-2-21 test method EN14582. 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Intlvac Thin Film Corporation, 1401 Duff Dr, Unit 600, Fort Collins, CO 80524, www.intlvac.com Liquid transfer pumpSection:ChooseTop of pageElastomeric primer and ad...Atomic layer deposition p...Cold cathode vacuum trans...X-ray fluorescence systemPrecision UV mirrorsSolder paste for fine-fea...Process for diamond-like ...Liquid transfer pump <<New literatureEllipsometer for thin-fil...Specialized vacuum gauges...CITING ARTICLES KNF has designed an economical solenoid-driven diaphragm pump for OEM users. The FL 10 pump features a nominal liquid flow rate of 100 mL/min against atmospheric pressure, simple linear flow rate adjustment, and a maintenance-free expected lifetime of 10 000 h. It can be operated to 14.5 psig (1 bar). Spring tension in the linear solenoid drive keeps the flow through the FL 10 tight in both directions when turned off and makes additional check valves unnecessary. 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KNF Neuberger Inc, 2 Black Forest Rd, Trenton, NJ 08691-1810, www.knfusa.com New literatureSection:ChooseTop of pageElastomeric primer and ad...Atomic layer deposition p...Cold cathode vacuum trans...X-ray fluorescence systemPrecision UV mirrorsSolder paste for fine-fea...Process for diamond-like ...Liquid transfer pumpNew literature <<Ellipsometer for thin-fil...Specialized vacuum gauges...CITING ARTICLES Vacuum process monitoring brochure Hiden Analytical has released a brochure on its quadrupole mass spectrometers for vacuum process monitoring. Systems cover the full pressure range from UHV for background species and leak detection to the millibar regime for process monitoring and control. The HPR-30 system addresses the higher-pressure regimes. It features integrated dry vacuum pumping and overpressure protection and is configured to mount directly to the process chamber. 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Hiden Analytical Inc, 37699 Schoolcraft Rd, Livonia, MI 48150, www.hideninc.com Ellipsometer for thin-film measurementsSection:ChooseTop of pageElastomeric primer and ad...Atomic layer deposition p...Cold cathode vacuum trans...X-ray fluorescence systemPrecision UV mirrorsSolder paste for fine-fea...Process for diamond-like ...Liquid transfer pumpNew literatureEllipsometer for thin-fil... <<Specialized vacuum gauges...CITING ARTICLES According to Horiba Scientific, its Uvisel Plus modular ellipsometer includes a new generation of the FastAcq acquisition technology, which can measure thin-film samples faster and more accurately than previously possible. The technology features new electronic data processing and a high-speed monochromator. Samples from 190 nm to 2100 nm can be measured within 3 min at high resolution. The technology allows for continuous adjustment of the spectral resolution along the measurement range. 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Horiba Scientific, 3880 Park Ave, Edison, NJ 08820, www.horiba.com Specialized vacuum gauges and controllersSection:ChooseTop of pageElastomeric primer and ad...Atomic layer deposition p...Cold cathode vacuum trans...X-ray fluorescence systemPrecision UV mirrorsSolder paste for fine-fea...Process for diamond-like ...Liquid transfer pumpNew literatureEllipsometer for thin-fil...Specialized vacuum gauges... <<CITING ARTICLES Edwards has released a range of passive gauges and controllers to meet the needs of users with specialized applications in the high-energy physics and UHV fields. The devices are suitable for a wide range of applications, from UHV systems to process industries, and for when an active gauge cannot be used. The passive gauges range from Pirani and Penning gauges to Bayard–Alpert and extractor ion gauge heads. They are used in conjunction with a passive gauge controller to display pressure and serve as an interface. 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Ballistic deposition model is a simple computational model described the growth of thin film with void defect. To make it more realistic, a surface diffusion process is added into the model. In this work, different interpretations of this process result in two different models, a “conventional” model and a “realistic” model. To see the difference between these models, the film’s morphology, interface width and defect density are studied. Simulation results show that the films from both models have smoother surfaces with less void defect density when the substrate temperature is increased. However, high substrate temperature leads to oscillations of the interface width curve in the conventional model while the curve of the realistic model maintains a power law relation with growth time. When studying the growth on patterned substrates, the realistic model was used. Two types of substrate, a flat substrate and a periodic patterned substrate, were studied. Persistence probability is a quantity that provides information on how much the pattern of the substrate is kept after the growth process is complete. Here, we found that the persistence probabilities of the films grown on both substrates decrease with the growth time. If the time is fixed, the substrate temperature plays an important role in controlling the film’s pattern. We found that there is only a narrow window of temperature that the film can maintain its original pattern longest. Also, we found that if the flat part of the substrate is larger, the original pattern of the film can survive longer.

An atomic layer deposition (ALD) method for coating metastable MoO2 thin films onto substrates was investigated. It is the first reported growth of metastable phased thin films based on chemical reaction-mediated thin film deposition processes, such as chemical vapor deposition or ALD.

Continuous, pinhole-free thin films of transparent conductive materials (TCMs) with p- and n-type conductivity are critical components of optoelectronic devices including photovoltaics (PV), transparent electronics, and LEDs [1]. TCMs with n-type conductivity are widely available in the form of semiconducting oxides [2]; however, p-type TCMs (hole transport materials, HTMs) with suitable conductivity are comparatively rare [1]. Particularly in the rapidly growing field of thin film perovskite PV, device-quality thin films of HTMs with high stability and conductivity are urgently needed to replace the organic HTMs typically employed in perovskite PV research [3]. As such, techniques to deposit inorganic HTM thin films are desired.With a focus on applying HTMs in optoelectronic devices at the commercial scale, these materials must be deposited by a scalable technique yielding thin, continuous, pinhole-free films. Chemical vapor deposition (CVD) is a highly scalable thin film deposition technique widely used in industry, with a proven ability to yield high-quality thin films on large-area substrates [4]. A variety of n-type TCMs are accessible by CVD techniques, but few CVD methods exist for p-type TCMs; examples include atomic layer deposition of NiOx and VOx [5].The cuprous halides (CuX, X = Cl, Br, I), which are optically transparent p-type semiconductors with bandgaps ~3 eV, are promising inorganic HTM candidates. Cuprous iodide is of particular interest due to its low resistivity (~10-2 Ohm·cm), high hole concentration and mobility (~1019 cm-3 and ~1-10 cm2V-1s-1, respectively), and its valence band maximum position (ionization potential: 5.0-5.4 eV), which is well-aligned with common perovskite absorber materials [6]. While CuI crystallite arrays have been obtained by metal-organic CVD [7], CVD of continuous CuI thin films has only been achieved by a two-step vapor conversion process, requiring initial deposition of a copper chalcogen followed by vapor-phase conversion to the halide [6].Our group has recently published a CVD technique enabling direct deposition of continuous CuBr thin films via CVD reaction between hydrogen bromide and vinyltrimethylsilane(hexafluoroacetylacetonato)copper(I) [Cu(hfac)(vtms)] [8], and this technique has been extended to deposition of CuI. X-ray photoelectron spectroscopy indicates pure CuI films with an atomic ratio of approximately 1:1 Cu:I, and x-ray diffraction confirms deposition of γ-CuI. Similar to our observations for CuBr films, substrate identity has significant effects on CuI film continuity. Progress towards CVD of continuous CuI films on substrates of interest for practical application in optoelectronic devices will be discussed, with a particular focus on perovskite PV.[1] A. N. Fioretti and M. Morales-Masis, "Bridging the p-type transparent conductive materials gap: synthesis approaches for disperse valence band materials," J. Photon. Energy, 10, 042002 (2020).[2] M. Morales-Masis, S. De Wolf, R. Woods-Robinson, J. W. Ager, and C. Ballif, "Transparent Electrodes for Efficient Optoelectronics," Adv. Electron. Mater., 3, 1600529 (2017).[3] B. Gil, A. J. Yun, Y. Lee, J. Kim, B. Lee, and B. Park, "Recent Progress in Inorganic Hole Transport Materials for Efficient and Stable Perovskite Solar Cells," Electron. Mater. Lett., 15, 505 (2019).[4] R. Gordon, "Chemical Vapor Deposition of Coatings on Glass," J. Non-Cryst. Solids, 218, 81 (1997).[5] J. A. Raiford, S. T. Oyakhire, and S. F. Bent, "Applications of atomic layer deposition and chemical vapor deposition for perovskite solar cells," Energy Environ. Sci., 13, 1997 (2020).[6] R. Heasley, L. M. Davis, D. Chua, C. M. Chang, and R. G. Gordon, "Vapor Deposition of Transparent, p-Type Cuprous Iodide Via a Two-Step Conversion Process," ACS Appl. Energy Mater., 1, 6953 (2018).[7] V. Gottschalch, S. Blaurock, G. Benndorf, J. Lenzner, M. Grundmann, and H. Krautscheid, "Copper iodide synthesized by iodization of Cu-films and deposited using MOCVD," J. Cryst. Growth, 471, 21 (2017).[8] C. M. Chang, L. M. Davis, E. K. Spear, and R. G. Gordon, "Chemical Vapor Deposition of Transparent, p-Type Cuprous Bromide Thin Films," Chem. Mater., 33, 1426 (2021).

Atomic layer deposition (ALD) has recently received increasing attention for the growth of high-conformity silicon nitride (SiN) thin films. In particular, plasma enhanced ALD (PEALD) allows SiN deposition at substantially lower temperatures (< 400 °C) with better film properties, compared to thermal ALD. These advantages make PEALD more attractive for ultra large scale integrated circuit (ULSI) device fabrication where the growth of aspect ratio independent and high-quality conformal thin dielectric films is tremendously important. The PEALD of SiN films involves a repetitive two-step process: (1) adsorption and decomposition of silicon-containing precursors and ii) nitridation of the Si-rich surface by active N species emanating from the plasma. Halogenated silanes such as hexachlorodisilane, bis(tertiary-butyl-amino)- silane, and dicholorosilane (DCS, SiH2Cl2) have been utilized as Si precursors. Despite previous studies, the underlying reaction mechanisms of these Si precursors with a N-rich SiN surface during PEALD still remain uncertain. Parameters controlling the rate of growth and uniformity have been demonstrated experimentally, but without knowledge of the reaction mechanisms, direct contributions of specific process conditions cannot be explained. Using first-principles density functional theory (DFT) calculations combined with experimental characterization, we have examined and identified a novel mechanism for the adsorption and decomposition of DCS on a N-rich SiN surface. Our study predicts that the DCS adsorption and dissociation can occur by overcoming a moderate barrier (~ 0.3 eV), far lower than the prohibitively large barriers predicted for previously proposed mechanisms. Through a detailed electronic structure analysis of the reaction intermediates, we have also elucidated the principles underlying the reaction mechanism, notably the hypervalent nature of Si which permits the facile reaction of molecularly adsorbed DCS with primary and secondary amines on the surface, followed by simultaneous Cl release and deportation steps and subsequent HCl formation and desorption. We have examined the same mechanism utilizing alternative precursors and the predicted trends are found to be corroborated with the important properties of the system. Understanding these principles allows us to develop guidelines for processing conditions, such as the importance of maintaining the proper surface composition to facilitate Si precursor adsorption and dissociation. Our study provides insight into the SiN ALD process via chlorosilanes and guidelines to control the deposition for high-quality SiN films and provides a framework for future theoretical studies of surface reactions during ALD.

Our laboratory is developing new chemical precursors for the growth of electropositive metal and element thin films by atomic layer deposition (ALD). We are also interested in processes that exhibit area selective growth. ALD has many current applications in copper metallization, diffusion barriers, liners, and transistor fabrication. Thermal ALD is often preferred because plasmas can afford low conformal coverage due to radical recombination on the walls of deep and narrow features. There has been extensive progress in the thermal ALD of copper and noble metal films in recent years, because the positive electrochemical potentials allow relatively easy reduction of precursor ions to the metals. Thermal ALD approaches to most other metals and elements in the periodic table are not well developed, due to the negative electrochemical potentials of the ions and a current lack of ALD co-reagents that can convert the ions to the metals or elements. Herein, we will describe the thermal ALD growth of electropositive metals such as nickel, cobalt, aluminium, and others. The ALD of nickel and cobalt metal films has been achieved using precursors containing diazadienyl ligands (precursors 1 and 2). These precursors enable the deposition of cobalt and nickel metal films at temperatures below 200 °C and use alkylamines as benign co-reagents. Growth rates are high (0.60 Å/cycle for nickel, 0.98 Å/cycle for cobalt), high purity, low resistivity metal films are obtained, and the films have low rms roughnesses. The processes exhibit inherent selective growth on metal substrates such as platinum, ruthenium, and copper. By contrast, no growth is observed on insulating substrates. We will also overview a new thermal ALD process for the growth of aluminum metal films. This process entails treatment of surface-bound AlCl3 with a thermally stable, volatile aluminium hydride co-reagent. The growth rate for the aluminium metal ALD process is high, and high purity, low resistivity aluminium metal films are obtained. Prospects for the area selective growth of aluminum metal films will be presented. These examples demonstrate that ALD processes can be enabled for electropositive metals through careful design of precursors and chemistry. Moreover, many of the metal ALD processes exhibit area selective growth. Figure 1

Chapter 6 - MOx materials by ALD method

Area-selective deposition (ASD) enables the growth of materials on target regions of patterned substrates for applications in fields ranging from microelectronics to catalysis. Selectivity is often achieved through surface modifications aimed at suppressing or promoting the adsorption of precursor molecules. Here we show, instead, that varying the surface composition can enable ASD by affecting surface diffusion rather than adsorption. Ru deposition from (carbonyl)- (alkylcyclohexadienyl)Ru and H2 produces smooth films on metal nitrides and nanoparticles on SiO2. The latter form by surface diffusion and aggregation of Ru adspecies. Kinetic modeling shows that changing the surface termination of SiO2 from -OH to -CH3, and thus its surface energy, leads to larger and fewer nanoparticles because of a 1000-fold increase in surface diffusion rates. Kinetic Monte Carlo simulations show that even surface diffusion alone can enable ASD because adspecies tend to migrate from high- to low-diffusivity regions. This is corroborated by deposition experiments on 3D TiN-SiO2 nanopatterns, which are consistent with Ru migrating from SiO2 to TiN. Such insights not only have implications for the interpretation of experimental results but may also inform new ASD protocols, based on chemical vapor and atomic layer deposition, that take advantage of surface diffusion.

Metal thin films are indispensable for the processing of a number of modern devices that benefit from their electronic, magneto-electric and optical properties. Application trends progressively involve integration into functional devices which feature three-dimensional nanostructures with increasingly high aspect ratios. These conditions promote increased interest towards non-line-of-sight deposition processes such as Chemical Vapour Deposition (CVD) and Atomic Layer Deposition (ALD). The deposition of metals using CVD or ALD is, however, less developed than that of the oxide counterparts. Several persisting limitations are directly related to the deposition chemistry. In the present perspective, relevant deposition chemical approaches are discussed along with their corresponding characteristics. Challenging issues regarding the purity and the nucleation kinetics are addressed. Using the intrinsic reactivity of the metals themselves to catalyse their own growth is one of the promising approaches emphasised here. Based on our recent work, the potential of this approach is discussed with respect to the growth of reactive and noble transition metals, pure or as alloys, as thin films or as embedded nanoparticles in functional oxide matrix thin films.

Transition from thin film to nanostructure in low pressure chemical vapor deposition growth of β-Ga2O3: Impact of metal gallium source

Weyl semimetals (WSMs) exhibit an electronic structure governed by linear band dispersions and degenerate (Weyl) points that lead to exotic physical phenomena. While WSMs were established in bulk monopnictide compounds several years ago, the growth of thin films remains a challenge. Here, we report the bottom-up synthesis of single-crystalline NbP and TaP thin films, 9 to 70 nm thick, by means of molecular beam epitaxy. The as-grown epitaxial films feature a phosphorus-rich stoichiometry, a tensile-strained unit cell, and a homogeneous surface termination, unlike their bulk crystal counterparts. These properties result in an electronic structure governed by topological surface states as directly observed using in situ momentum photoemission microscopy, along with a Fermi-level shift of −0.2 eV with respect to the intrinsic chemical potential. Although the Fermi energy of the as-grown samples is still far from the Weyl points, carrier mobilities close to 103 cm2/(V s) have been measured at room temperature in patterned Hall-bar devices. The ability to grow thin films of Weyl semimetals that can be tailored by doping or strain, is an important step toward the fabrication of functional WSM-based devices and heterostructures.

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