ICMCTF2016 Session H1: Advanced Microstructural Characterization of Thin Films and Engineered Surfaces

Wednesday, April 27, 2016 8:00 AM in Room Royal Palm 4-6

Wednesday Morning

Time Period WeM Sessions | Abstract Timeline | Topic H Sessions | Time Periods | Topics | ICMCTF2016 Schedule

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8:00 AM H1-1 Insights on the Early Growth Stages of Sputter-deposited Metallic Thin Films Gained from In Situ and Real-Time Diagnostics
Grégory Abadias, Jonathan Colin, Anny Michel, Cedric Mastail (Institut P’, Université de Poitiers, France)

The understanding of morphological and microstructural development during thin film growth is of particular relevance to control islands shape, nucleation and growth of nanoparticles, phase transformation, texture or surface roughness. Due to oversaturated vapor fluxes employed in physical vapor deposition (PVD) techniques, dynamics usually prevails over thermodynamics in dictating growth and microstructural evolution in PVD films. Depending on the material mobility, different growth modes occur, driven by kinetically limited surface diffusion processes and/or interfacial reactions. This has important implications in areas where nanoscale materials are involved, such as plasmonics, spintronics or next-generation of nano-devices.

In this presentation, we will provide some examples of in situ and real-time diagnostics based on optical techniques (wafer curvature, surface differential reflectance spectroscopy), X-ray diffraction and electrical resistance measurements to probe with high sensitivity the early growth stages of a variety of metal films on Si during sputter-deposition. In particular, we will show by coupling simultaneously two optical sensing techniques that the tensile stress generated upon island coalescence exhibit a maximum value at a film thickness that coincides with the onset of film continuity, for films growing in a Volmer-Weber mode (Ag, Au, Pd). The tensile stress magnitude is found to increase with decreasing material mobility, in relation with a lower percolation threshold, revealed from in situ resistivity measurement. For films with even lower adatom mobility (Fe, Mo), interfacial reaction with silicon favors a 2D growth mode and the initial formation of an amorphous film, followed by a phase transition to the equilibrium bcc phase above a critical thickness of ~2 nm. This transient phenomenon is manifested by a concomitant tensile stress variation and decrease in electrical resistance, which could be detected with sub-monolayer sensitivity thanks to the implementation of our in situ measurements.
8:20 AM H1-2 Plasma Assisted Nitriding of the FeAl40 Grade 3 Intermetallic Alloy
Julien Martin (Institut Jean Lamour, Université de Lorraine, France); Andrius Martinavicius (Université de Rouen, France); Stéphanie Bruyère, Hugo Van Landeghem (Institut Jean Lamour, Université de Lorraine, France); Frédéric Danoix, Raphaële Danoix (Université de Rouen, France); Thierry Grosdidier (Laboratoire LEM3 Université de Lorraine, France); Thierry Czerwiec (Institut Jean Lamour, Université de Lorraine, France)

Iron aluminides (Fe-Al) are attractive intermetallic compounds as lightweight and structural materials. From powder metallurgy routes, various oxide-dispersion-strengthened (ODS) versions of the FeAl intermetallic alloy have been developed - such as the FeAl40 Grade 3 alloy developped by CEA - to enhance the mechanical properties of the bulk material [1, 2]. However, the tribological performances of such materials remain poor and surface treatments are needed. In this context, the present communication presents some results on plasma assisted nitriding (PAN) for metallurgical surface modificationof the FeAl40 Grade 3 (ODS Fe-40at%Al) intermetallic alloy to improve the surface hardness and the associated wear resistance. Investigations are conducted to gain a deeper understanding on the mechanisms involved during nitriding of iron based aluminides, particularly those containing large amounts of Al (e.g. above 10 %).

Plasma nitriding was done using a 800 Hz pulsed d.c. plasma discharge containing a 95% N2 / 5% H2 gas mixture. The influences of the nitriding time (from 5 min to 48h) and temperature (from 400 to 645 °C) on the nitrided layer characteristics (thickness, morphology, element composition, crystallographic phase and hardness) were investigated. The nitrided layers were characterized at various scales (from 10 µm to 10 nm) with different analytical techniques: scanning electron microscopy (SEM), X-ray diffraction (XRD), electron-probe micro-analysis (EPMA), transmission electron microscopy (TEM) and atom probe tomography (APT).

Our results show that the growth kinetic follows a parabolic growth law as theoretically predicted by the Wagner’s theory where the mechanism of nitriding is mainly controlled by nitrogen diffusion in the a-Fe phase. It is also shown that, whatever the nitriding conditions used, the overall nitrided layers are divided into a thin outer sublayer of γ’-Fe4N phase (~1 µm in thickness) and a thick inner sublayer of hex. AlN and α-Fe phases (~10 – 100 µm in thickness).The combination of TEM and APT evidences a “eutectoid-like” morphology within the inner sublayer where α-Fe lamellae alternate periodically with α-Fe/ AlN lamellae (~300 nm in length and ~10 nm in width). The origin and influence of the nitriding conditions on this lamellar morphology will be discussed.

[1] MA. Munoz-Morris et al. Acta Mater. 2002;50:2825-36.

[2] F. Moret et al. J. Phys. IV 1995;6:281-289.

8:40 AM H1-3 Design of Multilayer Ti-TiN PVD Coatings with Tailored Residual Stress Profile
Marco Sebastiani (University of Rome "Roma Tre", Italy)

Multilayer systems can offer an efficient way of controlling residual stress, improve adhesion and enhance toughness of coated systems. This work aims at the development of multilayer coating with improved adhesion, based on numerical design approach. The numerical model of titanium–titanium nitride (Ti–TiN) multilayer has been formulated with multi-physics FEM and analytical modeling, to find the optimal thickness of individual layers in a multilayer that can decrease interfacial axial and in-plane shear stress. These coatings configurations are experimentally produced to quantitatively evaluate the scratch adhesion, in-plane residual stresses, nanoindentation hardness and elastic-modulus. The multilayer in comparison with standard single-layer shows significant improvement (22%) in adhesion under decreased interfacial stress conditions, without any affect on overall coating stiffness and hardness. The multilayer coating in comparison with different configurations was also investigated. Result shows an increase in scratch adhesion of 18% and 27% for the optimal position and thickness of interlayers respectively. Qualitative comparison of in-plane residual stress shows higher stress in bi-layer and lower stress in multilayer with optimal thickness of interlayer. The approach in the study could be used to develop stress-optimized coatings for wear resistance applications.

9:00 AM H1-4 Stress Analysis at Different Length Scales in Thermal Oxide Films Combining Raman Spectroscopy and X-Ray Diffraction
Mathieu Guerain (LCMO, CEA Le Ripault, Monts, France); Jean-Luc Grosseau-Poussard (LASIE, CNRS-Université de La Rochelle, France); Philippe Goudeau (PPRIME, CNRS- Université de Poitiers- ENSMA, France); Guillaume Geandier (IJL, CNRS-Université de Loraine, France); Benoit Panicaud (LASMIS, CNRS- Université Technologique de Troyes, France); Nobumichi Tamura (ALS, Lawrence Berkeley National Laboratory, USA); Catherine Dejoie (Laboratory of crystallography, ETH, Zurich, Switzerland); Jean-Sebastien Micha (Université Grenoble Alpes, CNRS UMR SPrAM, BM32 at ESRF, France)

Ability of Chromia-former alloys to form a thermal oxide scale allows reducing oxidation kinetics of the materials. However, durability of the metal/ceramic system depends on the mechanical integrity of this scale, and also of the scale damage such as buckling which could appear during oxidation and then cooling. These scale damages are closely correlated to the magnitude and sign of the residual stresses present in the oxide scale as well as to its microstructure i.e. grain size. In this work, an accurate determination of residual stresses in both Ni-30Cr and Fe-47Cr alloys at macroscopic scale in the adherent oxide and at local scale through damaged areas allows a comparison with models describing thin film delamination. A multi-scale approach is then proposed:

- At macroscopic scale, residual stress magnitudes are determined thanks to conventional XRD using sin2ψ method and Raman spectroscopy. The influence of metallurgical parameters on scale microstructural states and damage is studied.

- At microscopic scale, residual stress mapping through different types of delamination are performed thanks to Raman micro spectroscopy and Synchrotron micro diffraction. In this last case, the ability of switching the x-ray beam wavelength from poly to mono chromatic while keeping the beam at the same place on the sample surface allows studying alternatively the substrate and the oxide scale respectively.

Stress release modes by diffusional creep or delamination are studied and quantified. Morphological information and associated residual stresses allows confrontation to buckling mechanic and calculation of the interface toughness.

[1] M. Guerain, P. Goudeau, J. L. Grosseau-Poussard, Journal of Applied Physics 110, 093516 (2011)

[2] M. Guerain, P. Goudeau, B. Panicaud, J. L. Grosseau-Poussard, Journal of Applied Physics 113, 063502 (2013)

[3] M. Guerain, P. Goudeau, J.L. Grosseau-Poussard, Scripta Materialia 109, 15-18 (2015)

9:20 AM H1-5 Focused Ion Beam Methods for Micro-scale Residual Stress Assessment in Thin Films
Edoardo Bemporad, Marco Sebastiani (University of Rome "Roma Tre", Italy)

Analysis and control of residual stresses in advanced engineering materials are important issues for reliability assessment at small scales, e.g. for micro-electromechanical systems (MEMS) and nano-crystalline and amorphous bulk and thin film materials. This presentation gives an overview of the recent advances in the field of sub-micron scale residual stress assessment by the use of focused ion beam (FIB)-controlled material removal techniques.

The two step method consists of incremental FIB ring-core milling combined with high-resolution in-situ SEM-FEG imaging of the relaxing surface and a full field strain analysis by digital image correlation (DIC). The through-thickness profile of the residual stress can be also obtained by comparison of the experimentally measured surface strain with finite element modelling using Schajer’s integral method.

In this presentation, we will review the most recent advances in the field of FIB-DIC methods for residual stress assessment at the micro and nano scales, with focus on recent efforts for development of automated procedures for local residual stress analysis of (i) thin films, (ii) microelectronics devices and (iii) polycrystalline and amorphous bulk materials.

Practical applications of the method on several systems will be described and discussed. In particular, the issues of residual stress assessment on very thin films and micro-devices, stress depth profiling, stress measurement on amorphous materials and the effects of ion induced damage and elastic anisotropy on the relaxation strains will be reviewed.

10:00 AM H1-7 Limits of Determining Stress States by FIB Method due to Ga Implantation
Diana Courty, AllaS. Sologubenko (Laboratory for Nanometallurgy, ETH Zurich, Switzerland); StephanS.A. Gerstl (Scientific Center for Optical and Electron Microscopy, ETH Zurich, Switzerland); Ralph Spolenak (Laboratory for Nanometallurgy, ETH Zurich, Switzerland)
In order to assess the stress state in different kinds of materials in a reliable and flexible way, a Focused Ion Beam Microscope (FIB) routine has been developed to obtain information on the stress state in a material, in particular in thin films [A-C]. This method, named FIB-DIC micron-scale ring-core method, is based on monitoring relaxation of the material during a progressively deeper milling with a FIB beam. With digital image correlation (DIC), the change in the feature position can be analyzed and converted in residual strain and then with some modelling to residual stress. In order to standardize this incremental FIB-DIC micro-milling routine for the evaluation of intrinsic stresses at the sub-micron scale, the limits of the method need to be studied in detail.

One of the important questions is the limitation of the technique due to Ga implantation. In the present work we attempt to identify the zones impacted by FIB milling and the extent of Ga penetration and to determine the resolution limit of the method due to ion affected zones. Transmission Electron Microscopy (TEM) and Atom Probe Tomography (APT) are employed on a variety of materials to visualize and evaluate the Ga-induced zones. TEM is used to assess the nature and spatial distribution of the defects and to quantify the distribution of elements using Energy Dispersive Spectroscopy (EDS). A change of the structure in a Si-specimen, where the slightly thicker part of a TEM lamella was still crystalline, while the thinner part transformed to a fully amorphous state, could be observed.

For a systematic study of the Ga amount FIB has been used with different settings to implant Ga to a Si wafer and to a Si PSM (pre-sharpened mount), used for atom probe tomography. Raman spectroscopy has been performed on the Si wafer showing that no peak shift occurs and hence that there is no stress due to the implanted Ga. At the same time the peak intensity decreases with prolonged exposure time. Upon annealing the Si signal reappears, while Ga is visible as droplets on the surface. The local Ga concentration variations are analyzed as a function of ion implantation parameters. APT is used to assess the spatial distribution of Ga, after its implantation into the PSM via FIB and to visualize and quantify local concentration gradients and segregations that might be of interest.

[A] www.istress.eu

[B] Sebastiani et al., 2011, Mater. Sci. Eng. A, 528:7901–7908

[C] Korsunsky et al., 2009, Mater. Lett., 63:1961–1963

[D] Larson et al., 1999, Ultramicroscopy, 79:287-293

[E] Thompson et al., 2007, Ultramicroscopy, 107:131–139

10:20 AM H1-8 Advanced Characterization of Thermo-Mechanical Fatigue Mechanisms of Copper Systems for Semiconductor Metallizations
Stephan Bigl, Stefan Wurster (Montanuniversität Leoben, Austria); Megan Cordill (Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Austria); Johannes Zechner (KAI Kompetenzzentrum Automobil- u. Industrieelektronik GmbH, Austria); Daniel Kiener (Montanuniversität Leoben, Austria)

Two different electrodeposited copper films, ranging from 2.5 to 20µm thickness, were studied with regard to their thermo-mechanical fatigue behaviour via fast thermal cycling. Film A shows a constant grain size with varying film thickness, which is related to high incorporation of additives, whereas Film B is composed of a pure copper, leading to a film thickness dependency with respect to grain size. To study the film evolution during cycling, an advanced characterization method was implemented, combing area-specific topographical information using atomic force microscopy and microstructural information using electron backscatter diffraction. Assessing the information from the two techniques, obtained at the same area, enables to study the evolution of global parameters such as roughness, texture, average grain size and grain boundary characteristics. Furthermore, it allows the classification of the on-going fatigue mechanisms in the two film systems by examining the evolution of certain microstructural features and the mechanical properties by local nanoindentation. In addition, in-situ film stress measurements and film cross-sections were used for a more comprehensive interpretation. It was observed that starting with a similar initial microstructure, as it is the case for 5 µm film thickness, Film A shows a more stable microstructure, whereas Film B shows significant grain coarsening and greater film surface roughness, indicating that remaining additives play an important role in stabilizing grain boundaries during thermo-mechanical fatigue.

10:40 AM H1-9 ZNO Thin Films with Controlled Polarity and their Reactivity with Ti Studied by HAXPES
Ekaterina Chernysheva (Surface du Verre et Interfaces, UMR 125 CNRS/Saint-Gobain Recherche and INSP, UPMC, France); Nicola Bartolomei, Hervé Montigaud, Sergey Grachev (Surface du Verre et Interfaces, UMR 125 CNRS/Saint-Gobain Recherche, France); Rémi Lazzari (Institut des NanoSciences de Paris, UMR 7588 CNRS/UPMC Paris 6, France); Benjamin Dierre (NIMS Saint-Gobain Center of Excellence for Advanced Materials, Japan); Takeo Ohsawa, Kei Tsunoda (Optical and Electronic Materials Unit, NIMS, Japan); Naoki Ohashi (Optical and Electronic Materials Unit, NIMS and NIMS Saint-Gobain Center of Excellence for Advanced Materials, Japan); Bertrand Philippe, Håkan Rensmo, Olof Karis (Ångströmlaboratoriet, Uppsala Universitet, Sweden); Mihaela Gorgoi (Helmholtz-Zentrum Berlin für Materialien und Energie, Germany)

Wurtzite-type (WZ) semiconductors, including ZnO, are composed of cation and anion layers alternating along the <001> direction. This leads to the anisotropic properties of the basal surfaces of the WZ-type materials and their interfaces. [1-3] Recently, it was shown that it is possible to orient the growth of ZnO films with a chosen polarity by RF-sputtering deposition. [4] This presents a pending interest for applications related to ZnO interfaces with metals. In particular, for ZnO interfaces with Ti used either for Ohmic contacts, [5,6] or in thin film stacks in glazing industry, where the ultrathin Ti layer serves as an adhesion promoter in conducting glass. [7] Such interfaces are very sensitive to annealing. During a thermal treatment ZnO decomposes to oxidize Ti, and a ZnTiOx compound can be formed at the interface as a result of species diffusion. [8,9]

We report on an extended study of the ZnO films RF-sputtered on silicon wafers. At an elevated temperature the growth of ZnO thin films begins with the substrate oxidation. Zn vapour pressure is high, and most of the Zn atoms re-evaporate from the wafer surface. After a while, first ZnO grains nucleate. At this point the deposition conditions determine the orientation of the film which cannot be inversed after the nucleation stage. We demonstrate that the Zn orientation can be obtained only in a narrow range of the deposition conditions, as shown in Fig. 1. The grain size and defects in the ZnO films studied by a number of techniques vary as function of the deposition temperature and substrate bias. These properties of ZnO strongly affect its reactivity with Ti.

The Hard X-Ray Photoemission Spectroscopy (HAXPES) allows studying buried interfaces in a non-destructive way. This technique provides the information about the chemical environment of the sample with a nanometre in-depth resolution. We studied by HAXPES the reactivity of the obtained ZnO thin films covered by a 4 nm thick Ti layer as deposited and after annealing at temperatures up to 550 °C. We claim that a higher deposition temperature leads to more stable ZnO films. Thus, oxygen diffusion onset temperature is increased, and Ti stays under-oxidized even after annealing at 550 °C.


  1. N. Ohashi, et al., Jpn. JAP, 46, L1042 (2007)
  2. H. Tampo, et al., APL, 87, 141904 (2005)
  3. E. Barthel, et al., Thin Solid Films, 473, 272 (2005)
  4. J. R. Williams, et al., APL, 103, 042107 (2013)
  5. K. Ip, et al., JVST B, 21, 2378 (2003)
  6. U. Ozgur, et al., JAP, 98, 041301 (2005)
  7. S. Grachev, et al., Thin Solid Films, 518, 6052 (2010)
  8. J. Chen, et al., JES, 153, G462 (2006)
  9. R. Knut, et al., JAP, 115, 043714 (2014)
11:00 AM H1-10 FIB-TOF Characterization of Multi-Layer Thin Films
Dave Carr, Greg Fisher (Physical Electronics, USA); Shinichi Iida, Takuya Miyayama (ULVAC-PHI, Japan); Scott Bryan (Physical Electronics, USA)

There are practical limitations to depth profiling for probing the sample chemistry beyond the surface region which include preferential sputtering and accumulated sputter beam damage. Both effects result in a distortion or complete loss of the true 3D chemical distribution of multi-layer thin films.

An alternative approach to achieve 3D chemical imaging of complex matrix chemistries is to utilize in situ FIB milling and sectioning in conjunction with TOF-SIMS chemical imaging, or 3D FIB-TOF tomography [1]. This approach has already proven successful for inorganic thin film samples such as batteries and solid oxide fuel cells. In this presentation we will present new data where we have extended this method to organic multi-layer thin films.

The present study investigated samples from two classes of materials: one metal-organic mixed matrix composition and one mixed organic phase comprised of two polymer moieties. Since there was no preferential sputtering, an immediate result of the FIB-TOF imaging was the accurate determination of the depth scale. We have collected characteristic molecular information from each sample for the purposes of 2D and 3D imaging. Cluster ion beam polishing (e.g. Ar2,500+) was necessary to remove the FIB beam-induced damage, and the new instrument configuration allows cluster ion polishing to be accomplished with ease. We will highlight the instrumentation development and the methodologies which make FIB-TOF of organic thin films possible.

  1. A. Wucher, G.L. Fisher and C.M. Mahoney, Three-Dimensional Imaging with Cluster Ion Beams (p. 207-246) in Cluster Secondary Ion Mass Spectrometry: Principles and Applications, C.M. Mahoney (Ed.), Wiley & Sons, N.J. (2013).

11:20 AM H1-11 Diffusion Studies in the TiN/Cu Bilayer System and Beyond
Marlene Mühlbacher, Francisca Mendez-Martin (Montanuniversität Leoben, Austria); Bernard Sartory (Materials Center Leoben Forschung GmbH, Austria); Grzegorz Greczynski, Jun Lu (Thin Film Physics Division, IFM, Linköping University, Sweden); Nina Schalk (Montanuniversität Leoben, Austria); Lars Hultman (Thin Film Physics Division, IFM, Linköping University, Sweden); Christian Mitterer (Montanuniversität Leoben, Austria)

Continued device miniaturization in microelectronics calls for a fundamental understanding of diffusion processes and damage mechanisms in the Cu metallization/TiN barrier layer system. The starting point of the present study is a combined experimental and theoretical examination of lattice diffusion in ideal single-crystal TiN/Cu stacks grown on MgO(001) by unbalanced DC magnetron sputter deposition. After a 12 h annealing treatment at 1000 °C, a uniform Cu diffusion layer of 7-12 nm is observed by scanning transmission electron microscopy and atom probe tomography (APT). Density-functional theory calculations predict a stoichiometry-dependent atomic diffusion mechanism of Cu in bulk TiN, with Cu diffusing on the N sublattice for the experimental N/Ti ratio of 0.92.

These findings are extended to a comparison of grain boundary diffusion of Cu in dense polycrystalline TiN sputter-deposited on Si at 700 °C and underdense polycrystalline TiN grown on Si without external substrate heating. While the Cu diffusion path along dense TiN grain boundaries can be restricted to approximately 30 nm after a 1 h annealing treatment at 900 °C as visualized by 3D APT reconstructions, it already exceeds 500 nm after annealing at 700 °C in the underdense low-temperature TiN barrier. In this case, the formation of the Cu3Si phase, which characteristically grows along the close-packed <101> directions in Si, is identified as the main damage mechanism leading to complete barrier failure.

To meet the low-temperature processing needs of semiconductor industry and at the same time exploit the improved performance of dense polycrystalline barrier layers, deposition of Ti1-xTaxN barriers on Si is demonstrated by a reactive hybrid DC/high-power impulse magnetron sputtering process, where barrier densification is achieved by pulsed irradiation of the growth surface with only a few at.% of energetic Ta ions without external substrate heating. These barrier layers delay the onset of Cu grain boundary diffusion to temperatures above 800 °C (1 h annealing time) and are therefore capable of competing with TiN barriers deposited at 700 °C.

Time Period WeM Sessions | Abstract Timeline | Topic H Sessions | Time Periods | Topics | ICMCTF2016 Schedule