2017 Fall Meeting
MATERIALS AND DEVICESQ
Synchrotron radiation and atomic layer deposition for advanced materials
The symposium will bring together the atomic layer deposition (ALD) and synchrotron radiation (SR) communities to enable the application of SR to the study of the chemistry and materials science of thin films grown by ALD for leading-edge multiple technologies.
Despite that materials deposited by ALD are already at the production level, the ALD process is not yet fully understood and thin films deposited by ALD require more sophisticated investigation. Full understanding and control of the mechanisms underlying this growth method would lead to optimization of structure of the materials and better exploitation of their properties in devices. The use of synchrotron radiation (SR) techniques, both in-situ during ALD and ex-situ on ALD deposits to characterize both the early stage of the growth and the final products is a novel activity that is nowadays seeding at major synchrotron light sources all over the world. At the same time, many new types of ALD processes are being developed, including thermally, plasma or electron enhanced ones, as well as ALD processes for spatial pattering. ALD films are widely investigated to be used in:
- solar cells as electrode, barrier, or encapsulating layers
- LMR silica-fiber sensors,
- functional coatings for medical materials,
- GaN power devices,
- TSV field effect transistor,
The aim of this symposium is to gather the research communities involved in ALD and in SR and to provide a forum for them to discuss principles, results, and methodologies related to the study of ALD processes by SR experiments.
Papers relating to all aspects of the ALD, starting from different deposition method types and selection of precursors, going through laboratory- and synchrotron-based characterization methods of the surface, interface and ALD film growth and finally ending with potential applications of the ALD are invited.
Hot topics to be covered by the symposium:
- Characterization of ALD processes and materials (metals, oxides) using synchrotron light (PES, XANES, EXAFS, GISAXS, XRD, XRR, XRF, etc.)
- Investigation of ALD film nucleation, interface properties and growth by laboratory-based tools
- In situ/operando monitoring of ALD processes (APXPS, infrared spectroscopy, etc.)
- Modeling of the Atomic Layer Deposition
- ALD method types (thermal, plasma and electron enhanced, spatial, etc.)
- Application of ALD (solar cells, LED, HEMT, MIM capacitors, LMR silica-fiber sensors, GaN power devices, TSV field effect transistor, MEMS, etc.)
Tentative list of invited speakers:
- J. Dendooven (Ghent University, Belgium), ALD to grow metals - Pt
- S. Elliott (Tyndall National Institute, Ireland), Simulating Atomic Layer Deposition
- D. Fong (Argonne National Laboratories, USA), Applying in-situ X-ray scattering and fluorescence to monitor the ALD growth of materials
- E. Kessels (TU Eindhoven, The Netherlands), Application of ALD in solar cells
- J. L. MacManus-Driscoll (University of Cambridge, UK), Atmospheric pressure spatial atomic layer deposition of thin films: Reactors, doping, and devices
- M. Ritala (University of Helsinki, Finland), ALD of thin films for microelectronics
- T. Schenk (Namlab, Germany), ALD for memory devices
- J. Sprenger (University of Colorado at Boulder, USA) Low temperature Electron Enhanced ALD
- M. Tallarida (ALBA, Spain), Characterization of ALD processes and materials using synchrotron
Tentative list of scientific committee members:
- Manh-Hung Chu (Vietnam)
- Chittaranjan Das (Germany)
- Catherine Dubourdieu (Germany)
- Karol Froehlich (Slovakia)
- Karsten Henkel (Germany)
- Kamil Kosiel (Poland)
- Alessio Lamperti (Italy)
- Alex Martinson (USA)
- Uwe Schröder (Germany)
Manuscripts submitted to the Symposium Q, after peer-review process, will be published in the Synchrotron Radiation and Atomic Layer Deposition for Advanced Materials Special Issue of the Journal of Vacuum Science & Technology A in March/April 2018. Manuscript submission deadline is: November 15th, 2017.
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Advanced Characterization I : Malgorzata Kot
Authors : Massimo Tallarida
Affiliations : ALBA Synchrotron Light Source, Carrer de la llum 2-26, 08290 Cerdanyola del Valles, Spain
Resume : Atomic Layer Deposition is a powerful method to deposit very thin films of many classes of materials. The characterization of the ALD processes and of the properties of ALD materials is of immense importance for both the technological and scientific aspects. In the last decade, the development of synchrotron based techniques to study atomic layer deposition has been constantly growing, and nowadays it is possible to find beamlines which are specialized in performing in-situ ALD experiments. In this talk I will report on some of the most recent developments in the field of synchrotron radiation techniques to study ALD, and discuss possible future directions.
Authors : P. Hönicke, M. Müller, B. Beckhoff
Affiliations : Physikalisch-Technische Bundesanstalt (PTB), Abbestr. 2-12, 10587 Berlin, Germany
Resume : Reference-free X-ray spectrometry based on radiometrically calibrated instrumentation , which ensures the physical traceability of quantification to the SI units, is a unique feature of PTB. For X-ray spectrometry, various instruments and different beamlines are available at PTB’s laboratory at BESSY II in the spectral ranges of soft and hard X-rays (78 eV to 10.5 keV), as well as the “BAMline” for photon energies up to 60 keV [2–4]. With reference-free X-ray spectrometry, a non-destructive and quantitative characterization of nanolayers in a broad regime with respect to their thickness is enabled . Sub-monolayers of material as well as complex stacks of different nanoscale materials can be characterized with respect to their mass depositions, their depth dependent composition or their chemical species. In the present work, several ex-situ application examples of the reference-free X-ray spectrometry techniques to various atomic layer deposited materials will be presented. Using a combined synchrotron-based reference-free Grazing Incidence X-ray Fluorescence (GIXRF) and X-Ray Reflectometry (XRR) methodology , one can reliably perform a quantitative in-depth characterization of nanoscale layers and layer stacks. By applying X-ray absorptions spectroscopy (XAS), also information about the chemical species and the crystallinity can be obtained. References  B. Beckhoff, J. Anal. At. Spectrom., 23, 845 (2008).  F. Senf et al., J. Synchrotron Rad. 5, 780 (1998).  M. Krumrey et al., Nucl. Instrum. Meth.A 467–468, 1175 (2001).  W. Görner et al., Nucl. Instrum. Meth. A 467–468, 703 (2001).  M. Müller et al., Materials 7(4), 3147 (2014).  P. Hönicke et al., Phys. Stat. Solidi A 212(3), 523 (2015).
Authors : G. Laricchiuta, W. Vandervorst, J. Meersschaut
Affiliations : K.U.Leuven, IKS, Celestijnenlaan 200D, B-3001 Leuven, Belgium, imec, Kapeldreef 75, B-3001 Leuven, Belgium; K.U.Leuven, IKS, Celestijnenlaan 200D, B-3001 Leuven, Belgium, imec, Kapeldreef 75, B-3001 Leuven, Belgium; imec, Kapeldreef 75, B-3001 Leuven, Belgium.
Resume : Ruthenium thin films are considered for various applications in microelectronics, such as for electrodes in dynamic random access memories and for advanced interconnects. Atomic layer deposition (ALD) is believed to meet the requirements for sub-nm thickness control and conformality. Although the principles of ALD were developed more than 50 years ago, many physicochemical processes that influence the ALD growth are not entirely unraveled. It is recognized that Rutherford backscattering spectrometry (RBS) allows the quantification of thin film thicknesses to control the ALD growth as a function of different parameters (i.e. substrate, temperature, precursors). In this paper, we present the realization of an improved RBS set-up to reach a better limit of detection, and to enable more systematic RBS analyses of the ALD processes. The improvements to RBS relate to the implementation of multiple detectors (x10) and the realization of the multi-detector data acquisition. We describe the charge sensitive preamplifier module, which is optimized in terms of cost, form factor and noise pick-up. The data acquisition is based on a digitizer board (i.e. CAEN V1725), using the trapezoidal filter pulse processing . We analyze the energy resolution as a function of the trapezoidal parameters, and compare the energy resolution of the multi-detector system with the performance of a single-detector system. Finally, we demonstrate that, in case the surface approximation applies, the spectra from the individual detectors can be elegantly combined, and the analysis reduces to the one of a single spectrum. The advanced capabilities of the system are used to probe the incipient ALD growth process of ultrathin films of Ru. The multi-detector system proves to be distinctly advantageous in terms of limit of detection and measurement speed. We demonstrate the quantification of as low as 0.04 ML of Ru with a statistical uncertainty of 5%. On the other hand, the advanced measurement speed allows for a systematic investigation of the ALD growth process. We benefit of the advanced analysis capabilities to investigate the initial growth and inhibition of ruthenium on various substrates. Keywords: ALD, RBS, high throughput analysis, limit of detection. Reference  V. T. Jordanov, G. F. Knoll. Nucl. Instr. Meth. A 345 (1994) 337-345.
Authors : E. Atosuo, M.J. Heikkilä, V. Miikkulainen, M. Vehkamäki, M. Ritala, M. Leskelä
Affiliations : Department of Chemistry, P.O. Box 55, FI-00014 University of Helsinki
Resume : Alkali metal containing ternary oxides are of interest due to their suitable properties e.g. for batteries and piezoelectric devices. Many have been grown by atomic layer deposition (ALD) combining alkali metal oxide and metal oxide subcycles.[1–3] Alternatively, the formation of LixNbOy, LixTaOy and LixTiOy by solid state reaction of ALD grown lithium carbonate and metal oxide films was demonstrated by Atosuo et al. As both approaches usually require thermal treatment for obtaining the final structure, in situ methods like high temperature x-ray diffraction (HTXRD) and reflectivity (HTXRR) are useful for screening suitable conditions and observing changes during the annealing. Here we present HTXRD and HTXRR studies on formation of AxMOy (A = Li/Na, M = Nb/Ti/Hf) from ALD grown bilayer of A2CO3 and MOx. By combining the two x-ray methods one can acquire information about mixing, crystallization, surface/interface properties of the layers and alkali metal diffusion into the substrate. According to the HTXRD, the LiNbO3 phase is formed at 475 °C when heated in air. HTXRR data indicates that the topmost Li2CO3 layer is changing already above 330 °C and a single layer is formed above 420 °C, showing great benefit of having in situ XRR data in addition to XRD. Formation of NaxNbOy was found to be similar to that of LiNbOx. On the other hand, no LixHfOy formation but lithium diffusion into the substrate was observed for Li2CO3+HfO2 bilayer even though HfO2 lattice changes during annealing were evident. This presentation shows results on similar studies conducted on other above mentioned materials and discusses potential benefits of in situ synchrotron studies. 1. E. Østreng et al., J.Mater.Chem.C, 1 (2013) 4283 2. Liu et al., J.Mater.Chem.A., 3 (2015) 24281 3. Sønsteby et al., J.Vac.Sci.Technol.A, 34 (2016) 041508 4. Atosuo et al., Chem.Mater. 29 (2017) 998
Authors : R. Ciprian (1), A. Lamperti (2), L. Capasso (1), E. Cianci (2), D. H. Douma (3), A. Debernardi (2)
Affiliations : (1) Elettra Sincrotrone di Trieste, s.s. 14, km 163.5, 34149 Basovizza, Trieste, Italy; (2) Laboratorio MDM, IMM-CNR, via C. Olivetti 2, 20864 Agrate Brianza (MB), Italy; (3) Faculté des Sciences et Techniques, Université Marien Ngouabi, Brazaville, Congo
Resume : Diluted magnetic oxides are driving increasing interest in solid state physics and materials science communities for their potential applications in spintronic devices where they allow to reduce power consumption and to store and manipulate non-volatile data beyond room temperature, as requested in nano-electronics. Among oxides, ZrO2 is a promising candidate with a high dielectric constant and ionic conductivity which has recently been integrated in ultra-scaled devices. Fe is substitutional dopant that stabilizes the tetragonal phase of Zirconia . Exploiting x-ray absorption near edge spectroscopy (XANES) in high magnetic fields, we investigated the magnetic properties of thin films grown by atomic layer deposition (ALD) of zirconia doped with magnetic impurities. The spectra were acquired at Fe-L2,3, and O-K edges of iron-doped zirconia (ZrO2:Fex) for different Fe dopant concentrations x, ranging from diluted (x ∼1-2 % at.) up to high ( x ∼ 25 % at.) concentration. By x-ray magnetic circular dichroism (XMCD), we carefully analyzed the temperature dependence of the magnetic moments of this dilute magnetic oxides from low (T=5 K) up to room-temperature, for different Fe concentrations determining the best dopant range maximizing the magnetic signal. The results underline a relation between the Fe3 /Fe2 ratio and the amount of oxygen vacancies responsible for the temperature dependence behavior of the magnetization and the degradation of magnetic properties at high dopant regime. By the comparison with ab initio simulations we enlighten the microscopic mechanisms responsible for this peculiar behavior.  D.Sangalli et al. Phys. Rev. B 87, 085206 (2013). Douma, et al. Phys. Rev. B 90, 205201 (2014).
Advanced Characterization II : Gianluca Ciatto
Authors : Jolien Dendooven , Eduardo Solano , Ranjith K. Ramachandran , Matthias Minjauw , Alessandro Coati , Daniel Hermida-Merino , Christophe Detavernier 
Affiliations :  Ghent University, Dept. of Solid State Sciences, COCOON group, Belgium;  Synchrotron SOLEIL, SixS beamline, Saint-Aubin, France;  ESRF, DUBBLE BM26B beamline, Grenoble, France
Resume : Supported noble metal nanoparticles (NPs) are widely used in heterogeneous catalysis. ALD can be used to synthesize noble metal NPs on different high surface area supports, and offers sub-monolayer control over the metal loading. However, an improved understanding of how the deposition parameters influence the formation and growth of noble metal NPs is required to fully exploit the tuning potential of ALD. In addition, it is important that the synthesized NPs remain stable at the elevated temperatures typically required to carry out the catalytic reactions. Particle coarsening, leading to a loss of active surface area, is the main cause for a diminishing activity and/or selectivity of NP catalysts. We developed a synchrotron-compatible high-vacuum setup that enables in situ X-ray fluorescence and grazing incidence small-angle X-ray scattering monitoring during ALD growth as well as during thermal treatments [Rev. Sci. Instrum. 87, 113905, 2016]. Firstly, we investigated how the choice of reactant affects the island growth during ALD of Pt with the MeCpPtMe3 precursor at 300 °C. While surface diffusion of atoms and/or clusters was found to play an important role during the conventional O2 gas-based ALD process, a static growth mode was observed for Pt ALD using N2 plasma as reactant. Secondly, in situ GISAXS was used to investigate the morphological evolution of ALD-grown Pt NPs during annealing under different O2 partial pressures. A systematic study revealed that the as-deposited morphology and O2 concentration largely influence the onset temperature for Pt coarsening: bigger and more widely spaced NPs as well as larger O2 concentrations entail a higher onset temperature for coarsening.
Authors : S. Vangelista 1, R,. Piagge 2, S. Ek 3, T. Sarnet 3, A. Lamperti 1
Affiliations : 1 Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, I-20864 Agrate Brianza (MB) Italy; 2 STMicroelectronics, Via C. Olivetti 2, Agrate Brianza (MB) I-20864 Italy; 3 Picosun Oy, Tietotie 3, Espoo FI 02150 Finland
Resume : Recently CeO2 based materials are attracting renewed attention for their use in many applications. As such, CeO2 integration on substrate other than Si, such as TiN or metallic, is demanding; however only few basic studies exist on CeO2 deposited on metals. Our previous study showed that ALD grown CeO2 thin film deposited on Si or TiN substrate acquires a preferential orientation along <200> direction for CeO2/Si and <111> direction for CeO2/TiN. This finding is due to the competition of different energy components; in particular, the surface energy favors the <111> surface exposure, while the elastic energy accumulation is better sustained by <200> oriented grains. The energy components balance strongly depends on the reaction mechanisms occurring at the first stages of the deposition. To gain a deep insight into the growth mechanism, here we propose the use of grazing incidence small angle scattering (GISAXS) to determine the type of growth of ALD CeO2. By collecting GISAXS signal at synchrotron beamline during CeO2 in-situ ALD growth, we can understand the role of the substrate surface in dictating the growth mechanism, which in turn leads to a preferential orientation in the film crystallinity. Our results contribute to formulate an atomistic modeling of CeO2 growth by ALD. This work was partially supported by ECSEL-JU R2POWER300 project – grant agreement n.653933.
Authors : N. Nepal1, V.R. Anderson2, S.D. Johnson1, S.G. Rosenberg2, A.C. Kozen2, C. Wagenbach3, D.J. Meyer1, B.P. Downey1, J.K. Hite1, V.D. Wheeler1, Z.R. Robinson4, D. R. Boris1, S.G. Walton1, K.F. Ludwig3, and C.R. Eddy, Jr1
Affiliations : 1U.S. Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375, USA 2Postdoctoral Fellow, ASEE, 1818 N Street NW, Washington, DC 20036 3Physics Department, Boston University, Boston, Massachusetts 02215, USA 4Department of Physics, SUNY College at Brockport, Brockport, NY 14420, USA
Resume : InN and its alloys with GaN and AlN (III-N) have found application in a variety of technologies such as high power transistors, emitters, detectors, and solar-cells. The relatively high growth temperature of common III-N synthesis techniques has impeded further development and application of the materials due to challenges with miscibility gaps and strain related to thermal expansion mismatch with non-native substrates. To address these challenges, plasma assisted atomic layer epitaxy (PA-ALE) offers a new approach to low temperature III-N growth and can be used to epitaxially grow InN by using alternating pulses of trimethylindium and nitrogen plasma . Since growth using this technique is far from thermodynamic equilibrium, understanding how the nitrogen plasma pulse affects nucleation and growth kinetics is essential for development. Real-time grazing incidence small angle x-ray scattering (GISAXS) measurements have been used to monitor PA-ALE growth at synchrotron source facilities . In this paper we present the effect of variation in nitrogen plasma pulse conditions on PA-ALE of InN at 250 °C on sapphire substrates using GISAXS at the Cornell High Energy Synchrotron Source. Current results show the evolution of GISAXS characteristics such as the correlated peak (CP) length scale in the Yoneda Wing (YW) directly relates to the surface roughness, impurities, and electrical properties of the material. During the initial cycles of InN growth, the diffuse specular reflection broadens and CPs start to evolve along the YW with different correlated length scales. For the nitrogen plasma pulse time (tp) of 15 seconds, the CPs have two different correlated length scales of 33.36 and 8.38 nm suggesting bi-modal growth. With increasing tp to ≥ 20s (the empirically optimal pulse length), single mode growth evolves with a CP length scale of 10.46 nm. Additionally at tp = 25s, the growth rate is largest (0.035nm/cycle – consistent with previously reported self-limited growth ) with root mean square surface roughness and carbon impurity at or below AFM and XPS sensitivity limits, respectively. Thus the nature of GISAXS CP directly relates to the material quality. GISAXS also shows that the N2/Ar flow ratio through the plasma significantly affects the nucleation and growth of InN. Plasma characterizations have been used to guide examinations of plasma flow ratios in an effort to correlate nucleation and growth variations with plasma species incident on the surface. Based on various ex situ characterization methods, the quality of the PA-ALE grown films is similar or better than the material grown by conventional growth methods, for example, molecular beam epitaxy at higher temperature (>400 °C) .  Nepal et al., Cryst. Growth and Des. 13, 1485 (2013).  Nepal et al., J. Vac. Sci. Technol. A, 35, 031504 (2017).  Kuo et al., Diamond & Related Materials 20, 1188 (2011).
Authors : Eduardo Salas-Colera (a,b), Juan Rubio-Zuazo (a,b), Germán R. Castro (a,b)
Affiliations : a) Instituto de Ciencia de Materiales de Madrid-ICMM/CSIC, Madrid, Spain; b) Spanish CRG BM25 Beamline SpLine at the ESRF, Grenoble, France.
Resume : La0.7Ca0.3MnO3 perovskite material shows a ferromagnetic-paramagnetic phase transition with a metal-insulator transition and colossal magnetoresistance behaviour near of room temperature. This material has been studied in ultra-thin films form to be used in magneto-electronic devices. The magnetic and electronic properties of this mixed-valence manganite get worse in thin film form. The generation of oxygen vacancies has been studied to control and enhanced the magneto-electronic properties in this material. The oxygen defects produce important changes in crystal structure and electronic transport properties of manganites samples. The Mn valence is reduced and the metal-insulator transition is shifted to lower temperatures due to the modifications in the Mn-O bonds produced by oxygen defects. Polarized X-Ray Absorption Spectroscopy (XAS) allow to study the structural properties of the first coordination shell. The polarized X-Ray source from synchrotron is used to distinguish between in-plane and out-of-plane contributions to XAS signal from octahedral MnO6 structure. Polarized-XAS characterization show clear evidences that the formation of oxygen vacancies is produced in the basal plane of the MnO6 block. This results confirm that the magnetoresistance properties are managed by the amount of oxygen content and where the vacancies are produced in the crystal structure. These results have been correlated with previous structural, electronic and transport properties carried out.
Authors : I.N. Demchenko1, Y. Melikhov2, P. Konstantynov1, R. Ratajczak3, A. Turos4, and E. Guziewicz1
Affiliations : 1 Institute of Physics, Polish Academy of Sciences, Aleja Lotników 32/46, 02-668, Warsaw, Poland; 2 School of Engineering Cardiff University, Cardiff, CF24 3AA, United Kingdom; 3 National Centre for Nuclear Research, Soltana 7, 05-400 Otwock, Poland; 4 Institute of Electronic Materials Technology, Wolczynska 133, 01-919 Warsaw, Poland
Resume : The resonant photoemission (RPES) experiment was used to investigate the ytterbium electronic states and their hybridization with valence electrons of zinc oxide. The measurements were performed at Elettra synchrotron facility (Trieste, Italy). The obtained data were used to establish the correlation between the optical properties and the electronic structure. Both commercial single ZnO crystals and epitaxial ZnO films grown at IP PAS by Atomic Layer Deposition (ALD) technique were under investigations. Ytterbium ions were incorporated into the ZnO matrix via ion implantation and subsequent annealing. We investigated samples containing different quantity of (co-)implanted RE atoms (fluence of Yb at the level of 1015 and 1016 cm-2). Prior to photoemission experiments, Ar+ sputtering and annealing of the investigated samples up to ~573 K were performed. Photoemission spectra were taken for the photon energy range 180-190 eV i.e. across the Yb4d – Yb4f photoionization threshold which allows observation the Fano resonance enhancement from the Yb4f electron shell. We found a inconsiderable but clear resonant enhancement of Yb4f states to the ZnO:Yb valence band at binding energy about 7.5 eV below the Fermi level. A weak Fano resonance is consistent with a large 4f14-delta occupancy. It was also found that ytterbium 4d level shows an extended multiple structure instead of a simple spin-orbit doublet for metallic ytterbium, which allows concluding that majority of ytterbium atoms are bonded to oxygen and indicates that one of the 4f14 electrons has been promoted to the valence level. The work was supported by the NCBiR (PBS2/A5/34/2013) and by the EAgLE project (FP7-REGPOT-2013-1, Project No. 316014).
POSTER SESSION : Malgorzata Kot, Claudia Wiemer, Gianluca Ciatto, Joachim Schnadt
Authors : Holger Beh(1), Daniel Hiller(1), Birger Berghoff(2), Margit Zacharias(1)
Affiliations : (1)IMTEK, Faculty of Engineering, Albert Ludwigs University Freiburg, Georges Köhler Allee 103, 79110 Freiburg, Germany (2)RWTH Aachen University, Institute of Semiconductor Electronics, Sommerfeldstr. 18, 52074 Aachen, Germany
Resume : In order to replace indium tin oxide (ITO) as the standard TCO (transparent conductive oxide) for industrial applications, a number of requirements have to be fullfilled. Additionally to the good conductivity, also a sufficient transparency has to be assured. Furthermore, also the long-term stability of the conductivity is a crucial point. Generally, the behavior of the TCO under stress like constant high-intensity illumination is interesting in order to guarantee that no significant changes take place neither in the behavior of the TCO nor in its morphology. All of the aforementioned points are investigated for ALD-ZnO by UV-Vis spectroscopy, conductivity measurements in the Van-der-Pauw geometry, PL spectroscopy, Hall measurements and SEM.
Authors : Karsten Henkel, Chittaranjan Das, Małgorzata Kot, Franziska Naumann, Hassan Gargouri, Dieter Schmeißer
Affiliations : Karsten Henkel, Chittaranjan Das, Małgorzata Kot, Dieter Schmeißer: Brandenburg University of Technology Cottbus-Senftenberg, Applied Physics and Sensors, K.-Wachsmann-Allee 17, 03046 Cottbus, Germany Franziska Naumann, Hassan Gargouri: SENTECH Instruments GmbH, Schwarzschildstraße 2, 12489 Berlin, Germany
Resume : Synchrotron-based valence band (VB) spectra of titanium oxynitride (TiOxNy) and dioxide (TiO2) films prepared by different atomic layer deposition (ALD) processes are comparatively investigated and correlated to electrical measurements. A band-gap narrowing is found when the nitrogen amount in the films is increased. The reduction of the optical band-gap is attributed to defects within the band-gap promoted by the nitrogen density of states. In the VB spectra, in-gap states are found at about 1 eV below the Fermi energy in all investigated TiO2 and TiOxNy ALD films. An exponential dependence between the current density and the in-gap state intensity is observed combining VB spectra and current-voltage data. Fixed oxide charges and hysteresis found in capacitance-voltage measurements seem, on the other hand, not to be influenced by the in-gap states. We state that the in-gap states have an excitonic or polaronic origin. The selection of the ALD process parameters can be used to tune the band-gap narrowing as well as the in-gap state intensity.   K. Henkel, C. Das, M. Kot, D. Schmeißer, F. Naumann, I. Kärkkänen, H. Gargouri, J. Vac. Sci. Technol. A 35 (2017) 01B135.
Authors : G. Ciatto , M. H. Chu [1,2], P. Fontaine , N. Aubert , H. Renevier , and J. L. Deschanvres 
Affiliations :  Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, 91192 Gif-sur-Yvette, France  International Training Institute for Materials Science, Hanoi University of Science and Technology, No 1, Dai Co Viet, Hai Ba Trung, Hanoi, Vietnam  Laboratoire des Matériaux et du Génie Physique, Grenoble INP—MINATEC, 3 parvis L. Néel, 38016 Grenoble, France
Resume : We present a new beamline of Synchrotron SOLEIL dedicated to the study of thin films, nanostructures, and advanced materials via x-ray diffraction and spectroscopy in the energy range 1.2–13 keV. This range covers most of the absorption edges of interest in the field of semiconductors and functional oxides. In order to meet the increasing demand of advanced real-time characterization of nanoscale materials, the SIRIUS beamline has been designed with remarkable dynamic characteristics. Mounted on a high-flux undularor source, it uses a fast monochromator featuring the new “direct drive” technology and a very fast and precise 7-circle diffractometer. SIRIUS hosts three end-stations which can be used for in situ characterization. The first is a small chamber, mounted on the kappa head of the 7-circle diffractometer and equipped with motors for surface alignment. This chamber allows us to perform GI-XRD at energy ≥ 4 keV, and XAFS/XRR down to 1.2 keV. The second end-station is an ALD/MOCVD reactor dedicated to in situ studies of oxides. This reactor is mounted on a six-axis tower, which substitutes the kappa head of the 7-circle diffractometer. The station allows us to perform GI-XRD, GI-XAFS, XRR and GI-SAXS, and has been recently used to monitor the incipient growth of ZnO thin films on different substrates. The third end-station is a 4-circle in-vacuum diffractometer for resonant studies at energies ≤ 4 keV. Some examples of recent in situ results obtained at SIRIUS are shown.
Authors : Mikko Ruoho, Carlos Guerra-Nuñez, Mikhail Polyakov, Xavier Maeder, Rachel Schoeppner, Aidan Taylor, Philip Spring, Bernhard Andreaus, Ivo Utke
Affiliations : Mikko Ruoho; Carlos Guerra-Nuñez; Mikhail Polyakov; Xavier Maeder; Rachel Schoeppner; Aidan Taylor; Ivo Utke EMPA, Swiss Federal Laboratories for Materials Science and Technology, Feuerwerkerstrasse 39, CH-3602 Thun, Switzerland Philip Spring; Bernhard Andreaus INFICON AG, Alte Landstrasse 6, LI-9496 Balzers, Liechtenstein
Resume : Plasma resistant ceramics such as Y2O3 and Al2O3 have raised interest to be used in improving the contamination control of semiconductor manufacturing processes, especially as stricter requirements are dictated by the miniaturization of semiconductor devices. Y2O3 is an especially interesting material for this purpose due to its high chemical and thermal stability, and the material has been observed to have significantly lower etching rates than Al2O3. Atomic layer deposition allows for the fabrication of conformal pinhole free films, making it an interesting method for deposition of protective layers for samples with complex geometries. We have deposited Y2O3 and Al2O3 thin films, as well as nanolaminates of the materials, using Y(MeCp)3, YCp3, TMA and H2O as the precursors. The films were exposed to indirect remote NF3 plasma, and the subsequently measured XPS spectra reveal the chemical changes occurring at the surface of the films due to the plasma exposure. The results show that most of the surface fluorination takes place within the first 5 min of plasma exposure. Y2O3 exhibits higher surface fluorination and the fluorination penetrates deeper into the film than is the case for Al2O3. This finding is consistent with that observed by Kim et al. Al2O3 appears to exhibit surface fluorine saturation, while the initial data suggest that for Y2O3 the surface fluorination appears to decrease with increasing exposure time.  Dae-Min, K. I. M., Kyeong-Beom, K. I. M., So-Young, Y. O. O. N., Yoon-Suk, O. H., Hyung-Tae, K. I. M., & Sung-Min, L. E. E. (2009). Effects of artificial pores and purity on the erosion behaviors of polycrystalline Al2O3 ceramics under fluorine plasma. Journal of the Ceramic Society of Japan, 117(1368), 863-867.  Kim, D. M., Lee, S. H., Alexander, W. B., Kim, K. B., Oh, Y. S., & Lee, S. M. (2011). X‐Ray Photoelectron Spectroscopy Study on the Interaction of Yttrium–Aluminum Oxide with Fluorine‐Based Plasma. Journal of the American Ceramic Society, 94(10), 3455-3459.
Authors : Sang-Ju Lee1, Shi-Joon Sung1, Jin-Kyu Kang1, Ju-Young Yun2, Dae-Hwan Kim1*
Affiliations : 1Convergence Research Center for Solar Energy, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu 42988, Korea; 2Center for Vacuum Technology Division of Industrial Metrology, Korea Research Institute of Standards and Science(KRISS), Daejeon, Korea
Resume : Recently AgBiS2, CuSb(S,Se)2, PbS, Sb2S3, and Sb2Se3 have attracted intensive attention as a low-cost and stable light absorbing materials. Among them, Sb2S3 binary chalcogenide compound is considered to be a promising photovoltaic material due to their relatively low toxicity, long term stability and earth abundant element availability. Sb2S3 in its crystalline form has a proper bandgap (1.7–1.8 eV), high absorption coefficient, large intrinsic dipole moment, high dielectric constant for frequencies in the visible range (9.6–14.4), and a good band alignment in combination with various hole transport materials. Also it can be easily deposited by different methods such as thermal evaporation, sputtering, chemical bath deposition (CBD), and atomic layer deposition (ALD). The most widely used method is CBD due to its simplicity. The main disadvantage of this method is that it is difficult to prevent the formation of Sb2O3 during the deposition of Sb2S3. In our previous work, we demonstrated that the ALD method inhibited the generation of oxide defect and provided the high efficiency and good reproducibility. Conventional Sb2S3-based solar cells has mainly used TiO2 as a n-type buffer layer or hole blocking layer. However, it has been recognized that, in the Sb2S3-based solar cells, a high-quality condensed TiO2 layer necessarily requires high-temperature treatment above 500 ℃. Such extreme conditions could limit the future development of Sb2S3-based solar cells, particularly in flexible or stretchable applications. Therefore, it is meaningful to explore the possibility of fabricating Sb2S3 solar cells at low temperature region. In our study, low temperature (110 ℃) ALD Zn(O,S) n-type buffer layer was deposited on a FTO substrate, and Sb2S3, Poly-3-hexylthiophene(P3HT) and Au were prepared sequently. The composition ratio of S/O and the change of band structure with different S/O ALD sub cycles were analysed. At specific composition of S/O, we could obtain high efficiency above 5% that is comparable to one from the Sb2S3 solar cells with conventional TiO2 blocking layer.
Authors : Lana Lee, Boadan Zhao, Dr Robert Hoye, Dr Dawei Di, Prof Judith Driscoll
Affiliations : University of Cambridge
Resume : Nickel oxide (NiOx) is a wide band-gap p-type semiconductor which has recently attracted attention as a stable hole-transport/electron blocking layer in organometal halide perovskite solar cells, whilst its optoelectronic properties also make it suitable for use in LEDs and TFTs. For these applications, films must be of high quality; dense, pinhole free and with good coverage, whilst a fast deposition method is desired if the films are to be compatible with scale up for large area fabrication methods. Atmospheric pressure spatial atomic layer deposition (AP-SALD) has been developed in our group to deposit high quality metal oxide films, such as ZnO, TiO2, Cu2O. Unlike conventional atomic layer deposition, where the sequential introduction of precursors to a substrate is separated by lengthy purge steps, the reactive metal and oxygen containing precursors are spatially separated. The vapours of the precursors flow through separate gas channels towards a moving heated substrate, resulting in deposition of a metal oxide film as the substrate scans backwards and forwards. Depositions are carried out under ambient conditions and at growth rates of up to two orders of magnitude faster than conventional ALD. We report the deposition of NiOx for the first time by this method, with a growth per cycle of 0.25 nm/cycle as determined by XRR. Furthermore, growth rates of 0.05 nm/s are achieved, making the deposition process up to 40 times faster than conventional ALD. XRD shows that films are crystalline and phase pure, while AFM shows that pinhole free films with <1 nm RMS roughness can be deposited on glass on areas of up to 30 cm2. The films also demonstrate very good electrical properties, with our prototypical perovskite solar cell devices achieving efficiencies of over 16%. Overall we aim to show characterisation of the growth, structural and electronic properties of AP-SALD NiOx films, and, through demonstration of good devices properties, the potential of this technique large scale growth of high quality optoelectronic materials.
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Low temperature ALD : Claudia Wiemer
Authors : Jaclyn K Sprenger (1), Huaxing Sun (1), Andrew S Cavanagh (1), Kathryn J Wahl (2), Alexana Roshko (3), Steven M George (1)(4)
Affiliations : (1) Department of Chemistry and Biochemistry, University of Colorado Boulder; (2) Chemistry Division, Naval Research Laboratory; (3) National Institute of Standards and Technology; (4) Department of Mechanical Engineering, University of Colorado Boulder
Resume : Electron enhanced atomic layer deposition (EE-ALD) can drastically reduce the temperatures required for film growth through electron stimulated desorption (ESD) of surface species. The desorption process creates highly reactive “dangling bond” surface sites. Precursors can then adsorb efficiently on the dangling bonds. EE-ALD enables deposition of thin films on thermally sensitive substrates and growth of laminate materials where alloying would occur at traditional processing temperatures. We have demonstrated the EE-ALD of polycrystalline GaN, BN, and amorphous Si at room temperature (27˚C). Film growth was performed using alternating exposures of the appropriate precursors and low energy electrons (~100 eV). X-ray reflectivity and spectroscopic ellipsometry measurements monitored linear film growth versus number of reaction cycles. Additionally, we observed some dependence of the growth rate on electron flux and electron energy. Growth rates varied from 0.2 Å/cycle for Si films to 3 Å/cycle for BN films. Depth-profiling using x-ray photoelectron spectroscopy demonstrated clean BN (1.3:1) films with < 3 at.% C and O impurities. Crystallites as large as 10 nm were observed by high resolution transmission electron microscopy and grazing angle x-ray diffraction for GaN films. EE-ALD should facilitate the deposition of a variety of ALD films at low temperature. Materials grown with hydride or halide precursors are all possible candidates due to their large ESD cross-sections.
Authors : A. Loiudice, S. Saris, E. Oveisi, D. T. L. Alexander, and R. Buonsanti
Affiliations : Department of Chemical Sciences and Engineering, EPFL Valais Wallis, CH-1951 Sion, Switzerland
Resume : In the last year, all-inorganic perovskite quantum dots (CsPbX3 QDs with X=Br,I,Cl) have emerged as a new class of semiconductor nanocrystals with improved optical properties compared to the well-studied cadmium based QDs.[1,2] One of the issue that still remain to be addressed for implementation in optoelectronic devices and for the exploration of their properties under ambient conditions is the lack of stability with respect to temperature, moisture and light exposure. We have successfully developed a low temperature atomic layer deposition (ALD) process for the deposition of a thin layer of metal oxide on a film of CsPbBr3 QDs that 1) protects the perovskite QDs from water and high temperature and 2) prevents dissolution of the bottom layer or anion exchange in a multi-layering process. The nucleation and growth process of AlOx on the QD surface was thoroughly investigated by a miscellanea of techniques which highlighted the importance of the interaction between the ALD precursors and the QD surface to uniformly coat the QDs while preserving the optoelectronic properties. These nanocomposites show an exceptional stability against exposure to air (for at least 45 days), irradiation under simulated solar spectrum (for at least 8h), to thermal treatment (at least up to 200ºC in air), and finally against immersion in water. The method was extended to assembly CsPbBrxI3-x QD/AlOx and CsPbI3 QD/AlOx nanocomposites which were more stable compared to the pristine QD films. 1) D. Bera, et al., Materials, 2010, 3, 2260. 2) L. Portesecu, et al., Nano Letters, 2015, 15, 3692. 3) A. Loiudice, et al., Angew. Chem. Int. Ed. 2017, accepted.
Authors : John L. Lyons and Steven C. Erwin
Affiliations : Center for Computational Materials Science, Naval Research Laboratory, Washington DC 20375
Resume : Atomic-layer deposition (ALD) is an attractive method for low-temperature growth of nitride semiconductors. However, carbon contamination remains a concern during ALD growth, since cation precursors frequently contain methyl groups. While plasma-assisted ALD can aid in lowering carbon incorporation, the optimal growth conditions for achieving minimal carbon concentrations are unknown. Using density functional theory (DFT) we have calculated the behavior of methyl groups on InN, GaN, and AlN surfaces. We determine the surface binding energies of these species, their interactions with atomic hydrogen (present in plasma-enhanced ALD), and the mechanisms for incorporation into the nitride lattices. We incorporate these DFT results into a kinetic Monte Carlo model, allowing us to predict the amount of carbon impurity incorporation as a function of growth conditions.
Authors : T. Homola, R Krumpolec, D. C. Cameron, PR. Zazpe, K. Prikryl, J. Macak, P. Maydannik, G. Natarajan
Affiliations : T. Homola, R Krumpolec, D. C. Cameron, Masaryk University, Czech Republic; R. Zazpe, K. Prikryl, J. Macak, University of Pardubice; Czech Republic P. Maydannik, E T Consulting, Finland; G. Natarjan, Indira Gandhi Centre for Nuclear Research, India
Resume : Zinc blende-structure copper(I) halide materials (CuHa) are direct gap semiconductors with band energies in the ultra-violet region. They have high exciton and bi-exciton binding energies which have the potential for laser action with very low lasing threshold. Thin films and nanocrystallites of CuHa have been deposited by evaporation, sputtering and molecular beam epitaxy. Recently, preliminary work has shown that ALD has the ability to deposit thin films and nanocrystallite arrays which exhibit the characteristic photoluminescence of zinc blende CuCl. This paper investigates the growth processes and crystal structure and shows that CuCl films can be grown within an ALD window which ranges from 50oC to 150oC using [bis(trimethylsilyl)acetylene] (hexafluoroacetylacetonato)-copper(I) and HCl in butanol as Cu and Cl precursors, respectively. Initial nucleation depends on the length of the post-Cl purge times with short purge time leading to faster nucleation. After nucleation the deposition rate is similar in both cases. In addition, the results of film deposition of CuCl and CuBr using alternative halogen precursors will be presented. The use of in-situ deposition of capping layers to prevent degradation of the CuHa due to atmospheric moisture and their effect on the stability and structure of the films will be described.
Authors : A. S. Gudovskikh, A.V. Uvarov, I.A. Morozov, A.I. Baranov, D.A. Kudryashov, E.V. Nikitina, K.S. Zelentsov
Affiliations : Saint-Petersburg Academic University, Hlopina str. 8/3, 194021, St.-Petersburg, Russia
Resume : Integration of III-V compounds with Si is of great interest for development of optoelectronics devices like light emitting diodes, solar cells and optical IC. However, high quality and long term stable devices require rather a lattice matched growth of III-V materials. Thus GaP is the best candidate to be grown on Si substrates because it has the smallest lattice mismatch with Si (less 0.4 %) beyond all binary III-V alloys. GaP has an indirect band with a gap of 2.26 eV being a promising material for barrier layers but it is unsuitable for active layers of top junction for multijunction solar cells based on Si. Lattice-matched GaP/Si superlattice is proposed to be used as an active material. According to theoretical estimation GaP/Si superlattice for Si(100) plane becomes a direct-gap . However, the growth of III-V and IV layers with sharp interfaces and controllable doping level is difficult to realize using conventional epitaxial technology of such as MOCVD and MBE. In this paper a new approach to growth GaP/Si quantum wells at temperatures not exceeding 400 °C is explored. The layers of GaP are grown by plasma enhanced atomic layer deposition, where the growth of Ga atom monolayer alternates with the growth of one monolayer of P atoms. While Si is grown using conventional PECVD mode with high hydrogen dilution.  P. J. Lin-Chung. Electronic Structures for (Si)m (GaP)n Superlattices. MRS Proceedings, 220 (1991) 589
ALD for photovoltaics : Karsten Henkel
Authors : W.M.M. Kessels
Affiliations : Department of Applied Physics, Eindhoven University of Technology
Resume : In recent years, it has been realized that the unique features of atomic layer deposition (ALD) can also be employed to face processing challenges for various types of solar cells. With this, ALD for photovoltaics (ALD4PV) has attracted great interest in academic and industrial research and it has even been introduced in high-volume manufacturing. In this presentation, the status of the use of ALD nanolayers in various solar cell technologies will be reviewed and their future prospects will be discussed. The presentation will focus particularly on (i) the application of ALD oxides, most prominently Al2O3, for the passivation of surfaces of high-efficiency silicon solar cells; (ii) the preparation of highly transparent conductive oxides (doped ZnO films and In2O3:H); and (iii) the use of ALD-prepared nanolayers in perovskite solar cells. Also some underlying aspects of the ALD processes and material systems will be addressed on the basis of results obtained by advanced characterization techniques and by in situ and in operandi studies that have been carried out.
Authors : Robert L. Z. Hoye(1,2) and Judith L. MacManus-Driscoll(2)
Affiliations : 1) Department of Physics, University of Cambridge, JJ Thomson Ave, Cambridge CB3 0HE, UK 2) Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, UK
Resume : Atmospheric pressure spatial atomic layer deposition (AP-SALD) has emerged as a competitive and appealing technique for rapidly depositing semiconducting oxides for electronics. The growth rates achievable have been demonstrated to be up to two orders of magnitude higher than conventional ALD, and yet the films have comparable quality, uniformity and conformality to the substrate. We will discuss the operating principles of AP-SALD and the variety of laboratory- and industry-based reactors that have been developed. These will include the reactors from our laboratory and how the design has evolved over time to achieve improved uniformity and conformal coverage of high-aspect ratio nanostructures. A selection of the broad range of n-type metal oxides that have been grown by AP-SALD will be explored, with particular emphasis on the effect of doping on tuning materials properties, such as bandgap and carrier concentration. We will also explore the narrower range of p-type oxides grown by AP-SALD, and highlight the growing importance of expanding upon the number of p-type materials explored for thin film devices. Finally, we will show how the rapid growth of oxides with controllable electronic properties by AP-SALD has been critical in enabling improvements in the performance of emerging thin film photovoltaic materials and perovskite light emitting diodes.[1,2]  R. L. Z. Hoye, et al., Adv. Mater., Accepted. DOI: 10.1002/adma.201702176  R. L. Z. Hoye, et al., Adv. Mater., 27(8), 1414-1419 (2015)
Authors : Ganna Chistiakova, Mathias Mews, Regan Wilks, Marcus Bär, Lars Korte, Bernd Rech.
Affiliations : Institute of Silicon Photovoltaics, Helmholtz-Zentrum Berlin; Energy Materials In-situ Laboratory Berlin (EMIL), Helmholtz-Zentrum Berlin
Resume : Recently tin oxide was employed as electron contact in perovskite solar cells and in silicon-perovskite tandem solar cells. The best silicon heterojunction-perovskite tandem employed SnO2 deposited by PE-ALD in the internal tunnel-recombination junction between two subcells. As a first step for the further optimization, we conducted a study of the growth of SnO2 on silicon using in-system XPS. We varied the SnO2 PE-ALD process by deposition temperature (120-250 °C), oxygen plasma step duration (2-8 seconds) and plasma power (200 to 500 W). Samples were grown on c-Si substrates, and in-system XPS was applied to measure the layer stoichiometry and to quantify carbon and nitrogen contamination levels. Additionally, optical (n,k) and electrical (conductivity) properties were measured. The main focus of our study is the dependency optoelectronic properties of SnO2 layers on their elemental composition. XPS analysis showed that all samples contained Sn, O, C and N peaks. O, C and N peaks contained signals originating from residuals of the metal-organic precursor. We find that OH residuals are detrimental to the conductivity of SnO2 and reached a resistivity of 1mOhm*cm. All SnO2 films contained carbon residuals, which are partly assigned to surface contamination and partly to carbon incorporated into the volume. In total the carbon content of the films varied from 13-30%. Increasing carbon content in the layer leads to an increase of the refractive index from 1.6 up to 1.71.
Authors : Karsten Henkel, Malgorzata Kot, Dieter Schmeißer
Affiliations : Brandenburg University of Technology Cottbus-Senftenberg, Applied Physics and Sensors, K.-Wachsmann-Allee 17, 03046 Cottbus, Germany
Resume : The evaluation of the electronic structure and intrinsic defect mechanisms in thin films is essential for their effective use in applications with desired functionality such as surface passivation schemes for solar cells [1,2]. We present a comparative study of Al2O3, HfO2, and TiO2 films grown by atomic layer deposition (ALD) [3,4]. These films were characterized by resonant photoelectron spectroscopy and by electrical measurements. For all films investigated intrinsic defect states within the electronic band gap were observed including excitonic, polaronic, and charge-transfer defect states, where their relative abundance is subject of the choice of ALD parameters and of the used substrate. The spectroscopic assigned in-gap defect states are related with electronic charges as determined in the electrical measurements. We determine the ionicity in these systems and find that, in particular, the polaronic charges correspond to the covalent fraction. We attribute them to quasi-free charge carriers. The excitonic defects are located around the Fermi energy. Their existence and abundance depends on structural defects within the ALD films.  G. Dingemans and W.M.M. Kessels, J. Vac. Sci. Technol. A 30 (2012) 040802.  M. Kot et al.: ChemSusChem 9 (2016) 3401.  S. Alberton Corrêa, S. Brizzi, D. Schmeisser, J. Vac. Sci. Technol. A 34 (2016) 01A117.  K. Henkel, M. Kot, D. Schmeißer, J. Vac. Sci. Technol. A 35 (2017) 01B125.
ALD for memories : Massimo Tallarida
Authors : T. Schenk1, A. Anspoks2, B. S. Johnson3, J. L. Jones3, C. Richter1, T. Mikolajick1, U. Schroeder1
Affiliations : 1 NaMLab gGmbH/TU Dresden, Germany; 2 Institute of Solid State Physics, University of Latvia, Riga, Latvia; 3 Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7907, USA
Resume : The discovery of ferroelectric (FE) behavior in 10 nm thin Si:HfO2 films  in 2011 has raised hope for further discoveries of up-to-now unknown FE material classes and for overcoming integration and scaling issues of ferroelectric memories. The proof of the originally claimed Pca21 phase succeeded just in 2015 . However, results obtained by transmission electron microscopy might not sufficiently reflect the structure of hafnia in the thin film capacitors (poor statistics, structure relaxation in the lamella). X-ray diffraction (XRD) provides improved sampling of the structure for a larger averaged description. However, the existence of multiple phases with overlapping and broadened XRD peaks and insufficient sensitivity to the oxygen ions hamper structural studies . Here, x-ray absorption spectroscopy comes into play. First, powder samples of different phases were measured at different temperatures to understand the different polymorphs under well-defined conditions and separate from each other. After that, thin-film capacitors of different compositions were studied and the differences in structure compared to electrical data and the structural data obtained for the bulk references.  T.S. Böscke et al. Appl. Phys. Lett. 2011, 99, 102903, DOI: 10.1063/1.3634052  X. Sang et al., Appl. Phys. Lett. 2015, 106, 162905, DOI: 10.1063/1.4919135  E. D. Grimley, T. Schenk et al., Adv. Electron. Mater. 2016, 2, 1600173, DOI: 10.1002/aelm.201600173
Authors : Henrik H. Sønsteby, Helmer Fjellvåg, Ola Nilsen
Affiliations : University of Oslo
Resume : Piezo- and ferroelectric thin films become more and more important in modern technology, with the ever increasing need of higher performing materials on smaller and smaller devices. Atomic layer deposition (ALD) can be used to deposit ferroelectric films, with routes for materials such as Pb(Zr,Ti)O3, BiFeO3, LiNbO3 and KxNa1-xNbO3 already available . Understanding the structural behavior of such films upon perturbation by an electric field is crucial to design materials with the necessary functional and mechanical properties for industrial use. This type of in situ probing of structure is not very common, but could make an interesting contribution to the field. In this work, we present deposition of ferroelectric LiNbO3 and KxNa1-xNbO3 by ALD, and point out some important advantages and disadvantages of using ALD to make these materials. Evidence of ALD-type growth is presented, and piezo- and ferroelectricity is shown using piezoelectric force microscopy and electrical measurements (hysteresis loops). Furthermore, together with SNBL@ESRF, we are currently working on an in situ probe for measuring crystal structure of the thin films upon perturbation by an electric field. This setup is currently under commissioning, but preliminary results on some powder samples are available. We can follow the elongation of the unit cell of a PMN-PZT piezoelectric in situ while varying the applied electric field. This way we can correlate structural changes to the hysteresis loop, giving us important insight in the structural changes around the loop. Changes in diffuse scattering around the peaks are also visible, possibly increasing the amount of information we can get out of these measurements. This setup already allows for reflection geometry, and can be used for thin films as soon as a sample stage that allows for electrical measurements have been constructed. In this talk we would like to present the possibilities of such a setup, and discuss what can be learned by doing this type of measurements. We also point out some important constraints of both the setup and the deposited materials. We foresee the possibility to do measurements on thin films come fall 2017.  H. H. Sønsteby et al., Adv. Mat. Interfac., 10.1002/admi.201600903 (2017)
Authors : Stephan Aussen (1), Alexander Hardtdegen (1), Katharina Skaja (1), Christoph Bäumer (1), Thomas Heisig (1), Alessandro Kovtun (2), Federico Motti (3),(4), Francesco Offi (5), Francesco Borgatti (6), Regina Dittmann (1), Susanne Hoffmann-Eifert (1)
Affiliations : (1) Peter Grünberg Institute and JARA-Fit, Forschungszentrum Jülich, 52425 Jülich, Germany; (2) Istituto per la Sintesi Organica e la Fotoreattività, Consiglio Nazionale delle Ricerche, via Gobetti 101, 40129 Bologna, Italy; (3) Istituto Officina dei Materiali (IOM)-CNR, Laboratorio TASC, in Area Science Park, S.S.14, Km 163.5, I-34149 Trieste, Italy; (4) Dipartimento di Fisica, Università di Milano, Via Celoria 16, I-20133 Milano - Italy; (5) Dipartimento di Scienze, Università Roma Tre, I-00146 Roma; (6) Istituto per lo Studio dei Materiali Nanostrutturati (CNR-ISMN), Consiglio Nazionale delle Ricerche, via Gobetti 101, 40129 Bologna, Italy
Resume : Redox-based memristive devices (ReRAM) are considered for future high-density non-volatile data storage due to significant advantages in speed, power and scalability. In contrast to standard crossbar and pillar-structured cells, most of the vertical 3D ReRAM approaches require the resistive switching oxide layer to be deposited on the chemically active non-noble metal electrode. In this study, dense Hf, Ta and Pt metal layers deposited by off-axis sputtering were transferred through an UHV tunnel into the atomic layer deposition system (ALD) for the growth of ultrathin layers of Al2O3 and TiO2. Angle dependent X-ray photoelectron spectroscopy with different take-off angles was utilized to determine the thickness of the interfacial metal oxide layer formed as well as the valence states of the involved metal cations. No PtOx was found at the oxide/Pt interface. In contrast, applying identical processes to Hf and Ta metal surfaces/films resulted in oxidized interfacial layers with a thickness of up to 6 nm depending on the materials and process parameters. A direct comparison between TiO2 and Al2O3 capping layers clearly verified that Al2O3 acts effectively as a diffusion barrier resulting in thinner HfO2 and Ta2O5 layers compared to the TiO2 deposition. Additionally performed hard X-ray photoelectron spectroscopy experiments allowed a more detailed analysis of the deeper interfaces up to the pure metal bottom layer to from a complete picture of the layer stack.
Authors : Paul R Chalker, Matthew Werner, Joseph W. Roberts and Richard J. Potter
Affiliations : School of Engineering, University of Liverpool, Liverpool, L69 3GH, U.K.
Resume : Low energy ion scattering (LEIS) provides an analytical tool for probing surface composition and structure on the angstrom to nanometre. These length scales are central to the processing of thin films in electronic devices such as resistive RAM (RRAM), insulated – gate power transistors and transparent electronics. We will report on the application of LEIS to the elucidation of ALD deposition processes and how it can provide information about four factors, namely: the growth per cycle; adatom incorporation into the growing film; the nature of ligand leaving groups; and film-substrate interfaces. The complementary nature of the information from ion scattering will be compared to that provided by photoemission and X-ray reflectivity measurements, as a means of high-lighting the synergies and challenges of exploiting synchrotron radiation to understand the structure of ultrathin films.
ALD for innovative applications : Joachim Schnadt
Authors : Mikko Ritala, Timo Hatanpää, Jani Hämäläinen, Miika Mattinen, Maarit Mäkelä, Katja Väyrynen and Markku Leskelä
Affiliations : Department of Chemistry, University of Helsinki, Finland
Resume : ALD has gained an important and rapidly increasing role in microelectronics. The main drivers for this growth have been the increasing needs of high conformality, uniformity and repeatability that derive from the device development toward increasingly three-dimensional structures and smaller layer thicknesses. In addition, introduction of new materials and novel patterning techniques have opened for ALD fast lanes to production. ALD technology consists of two main components: reactors and processes. As the reactors have reached a level meeting industry specifications, the future of ALD will depend largely on development of new processes. Indeed, the success of ALD is built on chemistry: the unique benefits of ALD can be exploited only when proper precursors undergoing saturative surface reactions can be identified for the material of an interest. Development of ALD precursors and processes has therefore been in a central role over the entire history of the ALD technique. The review of Miikkulainen et al.  lists 780 ALD processes for 160 materials with 300 metal precursors, yet there are lots of important materials that lack ALD processes and also many of the existing ones call for improvement. This presentation summarises our recent results on ALD process development for materials with expected interest in the future generations of microelectronics, like MoS2, ReS2, Au, Cu and Re. Further directions and challenges in ALD process and precursor development as well as needs for reaction mechanism studies will also be outlined.  V. Miikkulainen, M. Leskelä, M. Ritala and R. L. Puurunen, J. Appl. Phys. 113 (2013) 021301.
Authors : Kamil Kosiel1, Karolina Pągowska1, Yevgen Syryanyy2, Krystyna Jabłońska2, Marek Guziewicz1, Maciej Kozubal1, Mateusz Śmietana3
Affiliations : 1 Instytut Technologii Elektronowej, Al. Lotników 32/46, 02-668 Warsaw, Poland; 2 Institute of Physics PAS, Al. Lotników 32/46, 02-668 Warsaw, Poland; 3 Institute of Microelectronics and Optoelectronics, Faculty of Electronics and Information Technology, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland
Resume : Sensing properties of novel optical sensors strongly depend on properties of the thin film materials - such as electrical permittivity or optical properties and size or thickness – that these devices the most often require for initiating or modifying their sensorial response. In this work we studied structure, composition and optical properties of TaxOy nanolayers as a promising dielectric material that can be easily deposited by low-temperature (100C) atomic layer deposition (ALD) technique, for application in optical fiber sensor technology. The TaxOy planar test layers were deposited at the temperature 100C on glass and silicon using TFS-200 (Beneq) ALD system, with tantalum pentachloride and deionized water as chemical precursors, and 6N-purity argon as carrier/purging gas. Their properties were investigated using x-ray diffractometry, Ratherford-backscattering spectroscopy, x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE) performed in visible-to-near-infrared range. Experiments revealed total amorphousness of the layers and slight differences between compositions when deposited on different substrates, with lower O/Ta atomic ratio for glass-related layers. The compositions measured from layers’ surfaces towards the layer-substrate interface were not constant, with decreasing O/Ta atomic ratio in the near-surface range, indicated by XPS. The layers’ refractive indices were according to SE close to 2.08 (at 632 nm) with extinction coefficients negligible in the visible range. The TaxOy thickness ensuring maximum sensitivity was about 63 nm, when tested as an overlay for sensors based on optical fibers with induced long-period-grating patterns.
Authors : Oksana Yurkevich, Ksenia Maksimova, Alexander Goikhman, Alexey Grunin, Pavel Prokopovich, Alexander Tyurin, Polina Medvedskaya, Ivan Lyatun, Irina Snigireva, Anatoly Snigirev
Affiliations : Oksana Yurkevich, Ksenia Maksimova, Alexander Goikhman, Alexey Grunin, Pavel Prokopovich, Polina Medvedskaya, Ivan Lyatun, Anatoly Snigirev; Alexander Tyurin; Irina Snigireva Immanuel Kant Baltic Federal University, Nevskogo str. 14, Kaliningrad, 236041, Russian Federation; Research and Educational Center “Nanotechnologies and Nanomaterials”, G.R. Derzhavin Tambov State University, Zashitny pereulok 7, Tambov, 392000, Russian Federation; European Synchrotron Radiation Facility, 6 rue Jules Horowitz, Grenoble, 38043, France
Resume : Beryllium being one of the most transparent to X-ray radiation elements has become the material of choice for X-ray optics instrumentation, applicable at synchrotron radiation sources and free electron laser facilities. However, there is a significant drawback in utilizing Be optics due to material oxidation and subsequent degradation under synchrotron irradiation . Also there are serious health risks associated with a powder BeO which can be originated because of X-ray irradiation . Improved properties of X-ray optics in terms of their surface quality and higher stability in the powerful X-ray beams are required as the high-brilliant fourth generation of synchrotrons are being developed now. In this work we propose to apply protective coatings in order to seal off beryllium from the ambient atmosphere. Al2O3 was chosen as a protective layer due to its passivation properties and low X-Ray absorption coefficient. To provide a good adhesion of the thin film towards the substrate and to make conformal deposition on objects with complicated shape we opted for atomic layer deposition (ALD) technique. Samples of beryllium coated with ALD Al2O3 were tested under monochromatic, pink and white beams at the European Synchrotron Radiation Facility (ESRF), in order to establish the conditions which the samples could tolerate without radiation damage. X-ray treatment was implemented at various environments – vacuum, helium, nitrogen, argon and dry air of different pressure. Mechanical study, post-process visualization and chemical analysis were performed to check the coatings efficiency. 1. Gmur N. (1992). Nucl. Instrum. Methods Phys. Res., A319, 228-232. 2. Gmur N., (1988). Nucl. Instrum. Methods Phys. Res., A266, 362-274.
Authors : P. Gentile, A. Valero, D. Gaboriau, M. Boniface, D. Aldakov, S. Sadki
Affiliations : Univ. Grenoble Alpes, CEA, CNRS, INAC, SYMMES, F-38000 Grenoble
Resume : The current trend towards miniaturized and autonomous electronic devices requires innovative energy storage solutions. For instance, autonomous micro-sensor networks or implantable medical devices would need a robust power source with high cyclability and a large power density, which might be out of the scope of conventional battery technologies. For such applications, microsupercapacitors (µSCs) are promising alternatives, and their integration “on-chip” could allow significant innovations. However, finding a suitable “on-chip” µSCs technology implies addressing key challenges, such as temperature resistance, silicon industry compatibility and good electrochemical performances on a small footprint. Nanostructures such as SiNWs and SiNTrs demonstrated excellent cyclability with more than 1 million cycles of galvanostatic charge/discharge under a 4 V wide electrochemical windows in EMI-TFSI ionic liquid, with large power densities and good capacitance values. Moreover, the use of silicon for electrode material allows extremely interesting developments towards “on-chip” integration and potential scale-up production using standard silicon industry processes for small micro-sized energy storage devices. Furthermore, we have also investigated the impact of the addition of a high-k dielectric layer, such as Al2O3 as protective films on silicon nanotrees. The electrochemical performances was enhanced, allowing symmetric 2 electrodes device to reach an unprecedented cell voltage of 5.5 V, improving energy and maximum power densities compared to unmodified nanostructured silicon. The cyclability was also largely enhanced, with only 3% capacitance fade after 1 million galvanostatic charge/discharge cycles at 4 V, and no degradation even after several 100000 cycles over 5 V.
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ALD of ZnO : Kamil Kosiel
Authors : Simon D. Elliott, Glen N. Fomengia, Mahdi Shirazi*
Affiliations : Tyndall National Institute, Lee Maltings, Dyke Parade, Cork, T12 R5CP, Ireland * current affiliation: Dept. of Applied Physics, Eindhoven University of Technology email@example.com
Resume : One of the attractive features of atomic layer deposition (ALD) is that it works at much lower temperatures (e.g. 150-300°C) than comparable chemical vapour deposition processes, and this enables deposition onto thermally-sensitive substrates. In some cases, ALD can be achieved at even lower temperatures, but such temperatures often require plasma, as the thermal process may show too low a growth rate to be useful. The prototypical ALD process of trimethylaluminium (TMA) and water is one such example. Here the amount of alumina deposited in an ALD cycle drops steadily as the growth temperature is lowered below 200°C, whereas the growth rate is maintained even down to room temperature if TMA+O2-plasma is used. It has long been supposed that the reason lies in thermal activation being required for some reaction step within the overall ALD process. As outlined in this talk, recent experiments in various laboratories and calculations in our group have revealed what reaction step is involved, and this has modified our view of ALD surface chemistry. We first review experimental results from Eindhoven University of Technology that detect persistent methyl groups at the end of the H2O pulse in low temperature alumina ALD  and analogous results for zinc and tin oxide ALD from Stanford University . We then highlight the particular surface reactions that were previously computed to show coverage-dependent kinetics for alumina and hafnia ALD and what types of surface species can consequently be expected to persist at the surface . The theory could be confirmed if these species and their local environment could be detected by surface-sensitive techniques, such as those based on synchrotron X-ray radiation. We expect that these effects may be even more acute in the case of thermal ALD of nitrides with the less reactive co-reagent NH3. Finally, we contrast the thermal H2O mechanism with that predicted by DFT for TMA+O2-plasma.  V. Vandalon et al., Appl. Phys. Lett. 108, 011607 (2016).  A.J.M. Mackus et al., J. Chem. Phys. 146, 052802 (2017).  M. Shirazi et al., Nanoscale 7, 6311 (2015).
Authors : Holger Beh(1), Daniel Hiller(1), Michael Bruns(2), Alexander Welle(3), Hans-Werner Becker(4), Margit Zacharias(1)
Affiliations : (1)IMTEK, Faculty of Engineering, Albert Ludwigs University Freiburg, Georges Köhler Allee 103, 79110 Freiburg, Germany (2)Karlsruhe Institute of Technology, Institute for Applied Materials & Karlsruhe Nano Micro Facility, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany (3)Karlsruhe Institute of Technology, Institute of Functional Interfaces & Karlsruhe Nano Micro Facility, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany (4)RUBION, Zentrale Einrichtung für Ionenstrahlen und Radionuklide, Ruhr-Universität Bochum, Universitätsstr. 150, 44780 Bochum, Germany
Resume : The good intrinsic conductivity of ALD-ZnO in the range of ~5 mΩcm is widely known. Furthermore, these films are highly transparent with only ~2.5% light absorption. This leads to the question if it is possible to further increase the conductivity by variations in precursor choice, deposition temperature and ALD parameters (pump & dose times). We compared the conductivity of ALD ZnO films at different deposition temperatures for the precursors diethylzinc (DEZ) and dimethylzinc (DMZ). DEZ shows a lower refractive index, lower deposition rate and lower conductivity over the whole investigated deposition temperature range. The variation of pump and dose times shows promising results for further increasing the conductivity and decreasing the process time. Additionally, the long-term stability of the conductivity of ALD-ZnO was investigated(1). Finally, the origin of the intrinsic conductivity itself is identified to be a donor state at the ZnO conduction band created by hydrogen incorporation during deposition(2). (1) Beh et al., Journal of Vacuum Science and Technology A, 35, 01B127 (2017) (2) Beh et al., J. Appl. Phys (under review)
Authors : E. Skopin 1, L. Rapenne 1, H. Roussel 1, A. Crisci 3, E. Blanquet 3, G. Ciatto 4, J.L. Deschanvres 1, D.D. Fong 5, M.-I. Richard 2, H. Renevier 1 Corresponding author : Evegenii Skopin, firstname.lastname@example.org
Affiliations : 1 Univ. Grenoble Alpes, CNRS, Grenoble INP, LMGP, F-38000 Grenoble, France; 2 Aix-Marseille Université, CNRS, Université de Toulon, IM2NP UMR 7334, 13397 Marseille Cedex 20, France; 3 Univ. Grenoble Alpes, CNRS, Grenoble INP, SIMAP, F-38000 Grenoble, France; 4 Synchrotron SOLEIL - Beamline SIRIUS, L’Orme des Merisiers, Saint-Aubin, F-91192, Gif sur Yvette, France; 5 Argonne National Laboratory, 9700 S. Cass Ave., Argonne, IL 60439, USA
Resume : InGaAs is a III-V semiconductor of great interest for high-electron-mobility transistors or high-speed electronics. A critical issue in such applications is reducing the contact resistance between the metal and the active semiconductor. One solution is to decrease the Sсhottky barrier height, by insertion of an ultrathin (~1 nm) tunneling insulator layer (such as ZnO) in between the metal and semiconductor , but this requires precise control over growth of the insulating layer. We have studied the incipient stages of ZnO growth by Atomic Layer Deposition (ALD) on In0.53Ga0.47As (001) substrates by in situ synchrotron X-ray characterization, using a custom-built ALD reactor that can be installed to different synchrotron centers . We will show that the Zn fluorescence yield measured as a function of number of ALD cycles shows two growth regimes. One corresponds to the completion of an ultrathin ZnO (amorphous) layer (~1 nm) on atomically flat InGaAs, and the second to the growth of ZnO on top of this layer. These results are consistent with in situ X-ray absorption spectra (XAFS) and ex situ AFM images. Modeling of the film mean growth (FMG) rate helps to elucidate the different FMG curves as a function of the growth temperature. We will also demonstrate the existence of an amorphous to crystalline transition when the ZnO layer thickness is increased and provide results on contact resistance measurements.  dx.doi.org/10.1063/1.4813881  10.1021/acs.cgd.6b00844
Authors : Claire H. Burgess, Huda Ahli, Martyn A. McLachlan
Affiliations : Department of Materials & Centre for Plastic Electronics, Imperial College London, UK
Resume : Organic materials are key components of many emerging electronic devices such as solar cells and transistors. Their printability and flexibility make them attractive as carrier transport layers, insulators and for patterning. Inorganic materials such as ZnO are often used in combination with organics as semiconductors, and can also act as barriers to e.g. water vapour, increasing stability. Atomic layer deposition (ALD) is capable of growing ZnO at temperatures compatible with organics, but nucleation and growth varies with substrate due to the surface chemistry. Studies have previously reported examples of growth on polymer fibres, within bulk heterojunctions and on top of select materials. In this work we build on this by using a simple method to produce thin films of a large range of polymers and small molecules, and we employ top view transmission electron microscopy (TEM) to investigate the early ZnO growth behaviour. Analysis of crystallinity, nucleation density and element mapping enable us to draw comparisons, for example, growth on poly-4-vinylphenol is similar to on amorphous alumina due to the abundance of hydroxyl groups, producing a continuous, crystalline ZnO film with an orientation dependence on thickness. In contrast, materials such as PMMA and PCBM lead to island growth, resulting in porous ZnO layers with inferior barrier properties. TEM is combined with other characterisation techniques and the impact of growth behaviour on device performance is discussed.
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