ICMCTF2014 Session B2: CVD Coatings and Technologies

Thursday, May 1, 2014 8:00 AM in Room Golden West

Thursday Morning

Time Period ThM Sessions | Abstract Timeline | Topic B Sessions | Time Periods | Topics | ICMCTF2014 Schedule

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8:00 AM B2-1 Pulsed Direct Liquid Injection CVD: a High Potential Process for Advanced and Nanostructured Carbide and Nitride Coatings
Francis Maury, Aurelia Douard, Guillaume Boisselier (CIRIMAT, France); Frédéric Schuster (CEA, France)
The pulsed direct liquid injection (DLI) of precursors is an emerging technology to feed CVD reactors with high vapor flow rates. This allows for example to increase the size of the CVD reactors or to develop deposition processes for continuous scrolling treatments. This technique has been especially developed to deposit functional oxides with applications in microelectronics. The molecular precursors are generally dissolved in a solvent and the use of an oxygen partial pressure prevents contamination of the films by carbon. More recently, solutions were found to control the carbon incorporation into the films and new DLICVD processes were proposed for the deposition of non-oxide coatings. In this paper, it is demonstrated that this technology offers new opportunities for the deposition of metallurgical coatings as carbides and nitrides as well as multilayer nanostructured coatings, as required for high protective performances under extreme environment. For nanostructured coatings each component should grow at the same temperature and pressure, and the multilayer architecture is achieved by controlling alternatively the composition of the gas phase. Examples of DLICVD processes operating either under atmospheric or low pressure are described. This includes hard chromium based coatings (Cr, CrxCy, CrN) and refractory coatings SiC and HfCx. Furthermore nanostructured multilayer coatings as Cr/CrN and CrN/CrCx with a bilayer period as low as 50 nm have been grown at 500 °C . HfC/SiC multilayer coatings 5 µm thick were deposited at 750 ° C with a bilayer period of 100 nm, i.e. thickness of individual layer was 50 nm. Preliminary properties of these advanced coatings and some interesting effects as self-healing of microcracks occurring during the growth of multilayers and surfactant effect induced by the solvent vapor are discussed.
8:40 AM B2-3 Niobium Nitride Thin Films Deposited by High Temperature Chemical Vapor Deposition
Frederic Mercier (SIMaP CNRS/Grenoble INP/UJF, France); Stephane Coindeau (CMTC-SIMaP, France); Matthieu Benz (SIMaP CNRS/Grenoble INP/UJF, France); Alexandre Crisci, Thierry Encinas (CMTC-SIMaP, France); Guillaume Riado, Raphaël Boichot, Arnaud Mantoux (SIMaP CNRS/Grenoble INP/UJF, France); Carmen Jimenez, Francois Weiss (LMGP CNRS/Grenoble INP, France); Elisabeth Blanquet, Michel Pons (SIMaP CNRS/Grenoble INP/UJF, France)

Niobium nitride (NbN) is a well-known superconductor and is considered to be one of the promising cryoelectronic materials. Till now, the thin films necessary for superconductive devices are mostly synthesized by physical vapor deposition methods. The aim of this study is to introduce chemical vapor deposition technique, CVD, as an alternative technique to process superconducting niobium nitride thin films.

In this work, NbN thin films have been grown by CVD from ammonia NH3 (99.999 %) and Nb chlorides species NbClx, in situ produced via chlorination of high purity Nb wire (99.999%) with chlorine gaz Cl2 (99.999%). Substrates are C-plane (0001) monocrystalline hexagonal sapphire, A-plane (11-20) monocrystalline hexagonal sapphire, (111) monocrystalline cubic silicon carbide. Deposition temperature has been varied between 900°C and 1300°C. Without any post-deposition treatments, the thin films have been characterized by means of SEM (Scanning Electron Microscopy), XRD (X-Ray Diffraction), XRR (X-Ray Reflectometry), Raman spectroscopy and EPMA (Electron Probe Micro Analysis). In this presentation, the influence of experimental parameters (temperature, composition of the gas phase, substrate) on the composition of the thin film and its structural properties (crystal structure, growth direction, lattice parameter, orientation relation between the substrate and the thin film) will be given. In particular, the stability of the cubic structure, the only structure which has the superconductive properties, will be discussed regarding the growth parameters. Finally, the potentiality of the CVD technique to synthesize high quality niobium nitride thin films and multilayers structures will be presented.

9:00 AM B2-4 Diamond Coatings for the Machining of Composite Materials used in Aerospace Industry
Biljana Mesic, Martin Frank, Michael Woda, Werner Koelker, Oliver Lemmer, Christoph Schiffers (CemeCon AG, Germany)

Due to the characteristic and attractive combination of the high strength and low weight (high strength-to-weight ratio), the composite materials - carbon reinforced fiber plastics (CFRP) and CFRP stacked with aluminum and titanium - are used as construction material in aerospace industry. The machining of these extreme abrasive composite and sandwich materials brings new challenges for the modern cutting tools. These are the surface quality of the workpieces without fiber delamination or uncut fibers and the rapid tool wear. It has been demonstrated that diamond coated cutting tools are the proper choice for such applications, due to their outstanding hardness and reduced tendency to stick of the workpiece material.

The multilayer CVD diamond coating on cemented carbide tools developed by CemeCon AG is specially designed to resist wear, prolong the tool lifetime and enhance the machining performances. The remarkable good properties of these CVD diamond coatings produced by a special hot filament chemical vapor deposition (HFCVD) process combine the advantages of an adhesive layer with the fracture toughness of nano-crystalline diamond. The performances of these multilayer diamond films in CFRP are excellent. The much finer and smoother diamond coating on cutting tool enables the vibration free drilling which results in high surface quality of the workpiece without chatter marks.
9:20 AM B2-5 CVD Titanium Aluminum Nitride Coatings for Cutting Applications
Dirk Stiens, Thorsten Manns, Sakari Ruppi (Walter AG, Germany)
The first reports on aluminum-rich, fcc-phase Ti1-xAlxN coatings by thermal CVD were published in 2006. These coatings, which were produced in laboratory scale deposition equipment, were reported to outperform state-of-the-art CVD and TiAlN PVD coatings in cutting tests. Current research and development in industry therefore focuses on the scale-up of the deposition process. For the present work Ti1-xAlxN coatings were produced by thermal CVD in production scale equipment from the precursors TiCl4, AlCl3, and NH3. The coatings were characterized by X-ray diffraction, scanning electron microscopy and microhardness measurements. Coatings with h-AlN/fcc-TiN or fcc-Ti1-xAlxN structure were obtained. Milling tests against grey cast iron and steel show that dramatic tool lifetime increases are possible when phase content and structure of the coatings are properly controlled.
9:40 AM B2-6 Functionalization of Aluminium Nitride Grown by High Temperature Chemical Vapor Deposition
Michel Pons (Grenoble Institute of Technology, France)

Functionalization of aluminium nitride grown by high temperature chemical vapor deposition

M. Pons1*, R. Boichot1, E. Blanquet1, S. Lay1, F. Mercier1, D. Pique2

1Science et Ingénierie des Matériaux et des Procédés, SIMAP, Grenoble INP-CNRS-UJF, BP 75, 38402 Saint Martin d’Hères, France

2SPADE, 73800 Ste Hélène du Lac, France


The application of AlN films in optoelectronics, sensors and high temperature coatings is strongly dependent on the nano- micro-structure of the film, impurity level and defect density. AlN epitaxial thin (0.5 – 10 µm) and thick polycrystalline (> 10 µm) films were grown on different foreign substrates (sapphire, silicon carbide, graphite) and single AlN crystals by Chemical Vapor Deposition (CVD), also called Hydride Vapor Phase Epitaxy (HVPE), at high temperature (1200-1750 °C). In the first part of this paper, polycrystalline growth of thick films (>10 µm) prepared at high growth rate (>100 µm.h-1) was performed on graphite substrates to study the preferential orientation of the films. AlN/W multilayers were deposited on silicon carbide composites to increase their performance at high temperature in aggressive conditions. Such multilayer materials can be used for the cladding of nuclear fuel. The second part of this paper concerns the characterization of epitaxial films, including their crystalline state, surface morphology, and inherent and thermally induced stress which inevitably leads to high defect densities and even cracking. The full-width at half-maximum (FWHM) of X-Ray rocking curves of the grown AlN layers exhibited very large values (several thousand arcsec), and they became steeply deteriorated with increasing growth rate. To improve the crystalline quality of AlN layer, well-known growth techniques, such as multi-step growth using buffer layers, were used at temperatures above 1200 °C in order to lower the disorientation to 300 arcsec. The applications of such “templates” for deep UV light emitting diodes (UV LED) and surface acoustic wave sensors (SAW) are discussed.

10:00 AM B2-7 Diagnostics of SiH4/H2 Plasma and Surface Reaction in Microcrystalline Silicon Deposition
Kenji Ishikawa, Yusuke Abe, Atsushi Fukushima, Ya Lu, Sho Kawashima, Keita Miwa, Keigo Takeda, Hiroki Kondo, Makoto Sekine, Masaru Hori (Nagoya University, Japan)

The tandem solar cell was commonly fabricated by stack of hydrogenated micro-crystalline silicon (μc-Si:H) thin film for the bottom cell and amorphous silicon (a-Si:H) thin films for the top cell. The μc-Si:H can absorb light in higher wavelength towards the infrared region of the solar spectrum and has excellent stability against light soaking. However, the indirect optical transition of μc-Si:H is not efficiently absorbed sunlight, film thicknesses greater than 2 μm. To realize low-cost fabrication of solar cell with the plasma-enhanced chemical vapor deposition (PECVD) processes at low temperature, the high-rate growth of high-quality μc-Si:H films is required.

To date, the growth rate of approximately 2 nm/s was realized using a capacitively coupled plasma (CCP) system with a very high frequency (VHF)-power source and a high working pressure (ca. 1000 Pa) with a narrow electrode gap. In particular the relatively high working pressure, the high electron density is demanded on achievement effectively the SiH4 depletion. Moreover, the H radicals are recognized as a key factor that influences the crystallinity of Si thin films. Sufficient supply of H radicals to a growing Si thin film surface induces crystallization.

The SiH4/H2 gas mixture ratio was 3% with a total gas flow rate of 1000 sccm, and the total pressure was kept at 1200 Pa. The distance between the VHF and lower GND electrodes was 10 mm, and that between the VHF and upper GND electrodes was 5 mm.

The electron density in the SiH4/H2 plasma region was measured using a 35 GHz microwave interferometer. A multi-channel spectrometer was used to observe the optical emission intensity of the Si* (288 nm) and SiH* (414 nm) lines. The absolute density of H radicals was measured by vacuum ultraviolet laser absorption spectroscopy (VUVLAS).

The crystallinity factor, preferential orientation, defect density, micro-structure, and the post-deposition oxidation of deposited Si thin films were investigated by Raman spectroscopy, XRD, ESR, TEM, and FTIR, respectively. For the fabrication of Si thin films for solar cell devices to achieve selective enhancement of the H radical densities for crystallization of the films under low depletion of SiH4. From these results, we will discuss effects of those radicals on surface reaction in μc-Si:H deposition.

10:40 AM B2-9 In-situ Measurements of Volume Fraction of cDusters in Films During Plasma CVD
Masaharu Shiratani, Susumu Toko, Kazunori Koga, Naho Itagaki, Hyunwoong Seo (Kyushu University, Japan)
We have developed an in-situ measurement method of volume fraction Vf of clusters (nanoparticles) in films during deposition using quartz crystal microbalances with a cluster-eliminating filter [1, 2]. The cluster volume fraction has been determined by comparing deposition rates of the films with and without clusters. The cluster volume fraction gives useful information to control the incorporation of clusters into films [1-3]. We applied this measurement method to a-Si:H deposition by rf capacitively coupled discharge plasma CVD and obtained the following results. 1) Vf is the highest in 2 s after discharge plasma initiation and then decreases to a steady state value with a characteristic time of 50 s. This long characteristic time depends on gas composition change due to dissociation of molecules in the discharges and a rise of electrode temperature mainly due to ion flux to the electrodes. 2) Contributions of negatively and positively charged species to film deposition rate are less than a few %, namely, they are minor deposition species. 3) Typical size of clusters incorporated into films is less than 2 nm, deduced from force balance. 4) Amplitude modulated discharges with sine wave bing about lower initial Vf, shorter initial transient duration of Vf, and lower steady state Vf value. These results give insights into film deposition processes. Based on the insights we can improve significantly stability of a-Si:H films, which is the key to high efficiency Si thin film solar cells.
Work supported by MEXT, JSPS, JST, NEDO, and PVTEC.
[1] Y. Kim, et al., Jpn. J. Appl. Phys., 52, 01AD01 (2013).
[2] Y. Kim, et al., MRS Proc. 1426, 307 (2012).
[3] Y. Kim, et al., Surf. Coat. Technol. 228, S550 (2012).

11:00 AM B2-10 Microstructure and Wear Mechanisms of Texture-controlled CVD α-Al2O3 Coatings
Rachid M'Saoubi, Tommy Larsson (Seco Tools AB, Sweden)

The microstructure and wear mechanisms of texture controlled CVD α-Al2O3 layers with (0001), (01-12), and (10-10) growth textures were investigated in single point turning of AISI 1045. A wide range of cutting speed conditions and tool geometries were investigated to achieve broad combination of mechanical and thermal loads on the cutting tools that were also assessed experimentally.

The experimental coatings were investigated by FEG-SEM, EBSD and a combination of FIB and analytical TEM techniques prior to and after machining. Significant texture effects on wear performance of the α-Al2O3 coating layers were observed, confirming results from previous wear studies in the context of machining AISI 4140 carbon steel (Ruppi 2007, M’Saoubi and Ruppi 2009). The wear mechanisms of the coating layers are further interpreted in the light of thermal, mechanical and frictional conditions occurring at the tool–chip contact interface. In particular, it is suggested that the enhanced near surface deformation (0001) Al2O3 modifies the frictional conditions and heat dissipation at the tool-chip contact thus reducing the overall deformation of the cutting edge.
11:20 AM B2-11 Grain Boundary Engineered α-Al2O3 Coatings
Sakari Ruppi, Dirk Stiens, Thorsten Manns (Walter AG, Germany)

The introduction of texture-controlled deposition processes is one of the most important recent developments in CVD of α-Al2O3. Consequently, today it is possible to deposit α-Al2O3 coatings with several preferred growth directions e.g. (012), (110), (001) and (100). α-Al2O3 layers with 001 texture have been shown to be superior to all the other textures and randomly oriented α-Al2O3 coatings in many metal cutting applications and several manufacturers have introduced products based on this technology.

Grain boundary engineering is a promising way to further enhance the performance of the textured α-Al2O3 coatings and grain boundaries in CVD a-alumina have attained growing interest during the last few years. By controlling the preferred growth direction in the α-Al2O3 during deposition the grain-boundary distribution and morphology can be modified and controlled.

In this paper experimental α-Al2O3 coatings with different grain boundary structures and textures will be presented and discussed. The experimental α-Al2O3 were deposited on Ti(C,N) coated cemented carbide inserts to identical thickness for comparative cutting tests. In addition to the cutting tests, the coatings were analyzed in detail by using SEM, TEM, XRD and EBSD.

11:40 AM B2-12 Growth Mechanism of Amorphous Phase Mixed α-Al2O3 Hard Coatings
Sho Tatsuoka, Kenichi Sato, Naoyuki Iwasaki, Kenji Yamaguchi, Akira Osada (Mitsubishi Materials Corporation, Japan)

Chemical Vapor Deposition (CVD) method has been used for the industrial production of wear resistant coatings on cutting tools and Al2O3 coatings have been widely used to maintain high hardness and excellent oxidation resistance under such a severe cutting condition. It is well known that Al2O3 exhibits a number of crystalline polymorphs, such as α, κ, δ, θ, etc. However, there are few reports on crystalline-amorphous phase mixed Al2O3 thin films as wear resistant coatings.

In this work, we investigated growth mechanism of amorphous phase mixed α-Al2O3 thin films deposited using gas mixtures of trimethylaluminium, as aluminum precursor, O2, and Ar instead of conventional gas mixtures, such as AlCl3, CO2, and H2. The deposited Al2O3 layer is composed with high aspect ratio columnar-like α-Al2O3 grains and the amorphous Al2O3. The amorphous phase mixed α-Al2O3 thin films were prepared with several interface layers to control orientation and morphology of the α-Al2O3 grains. The α-Al2O3 grains show anisotropic growth enhanced along a-axis and suppressed along c-axis depending on the prepared interface layers.

12:00 PM B2-13 Chemical Vapor Deposition of Epitaxial sp2-Boron Nitride Thin Films
Mikhail Chubarov (Linköping University, IFM, Thin Film Physics Division, Sweden); Henrik Pedersen (Linköping University, Sweden); Hans Högberg, Anne Henry (Linköping University, IFM, Thin Film Physics Division, Sweden)

Thin films of boron nitride in the sp2-hybridized state (sp2-BN) is promising material for electronic and optoelectronic devices to be operated at high temperatures and in chemically demanding environments. This is due to high thermal and chemical stability, a wide band gap (~ 6 eV), low dielectric constant and the possibility of both p- and n-type doping.

A further advantage for sp2-BN is that the hexagonal basal plane exhibits the same structure as graphene, where the carbon atoms have been replaced by half nitrogen and half boron atoms. As a result the lattice mismatch between sp2-BN and graphene is only 2%. The structural similarity to graphene suggests additional applications as a dielectric substrate and gate dielectric in graphene electronics.

Despite the promising properties, sp2-BN is still the least investigated material among the III-nitrides, mainly due to limitations in depositing thin films with necessary quality.

In this study, we present results from growth of sp2-BN films by Chemical Vapor Deposition (CVD) focusing on the quality of sp2-BN films as a function of process temperature, precursor mixture as well as the effect of adding silicon during growth. .

The deposition of the films was conducted in a horizontal hot-wall CVD reactor using triethyl boron (TEB) and ammonia (NH3) as boron and nitrogen precursors. As substrate 0001 oriented a-Al2O3, 0001 oriented hexagonal silicon carbide (SiC) and 111 oriented cubic SiC were used. We have previously shown that an AlN buffer layer is necessary for the growth of rhombohedral BN (r-BN) of good quality on a-Al2O3 [1]. Our recent results obtained on SiC substrates suggest opposite behavior, when AlN is in-situ deposited on SiC prior to the BN deposition, i.e. AlN buffer layer is not necessary but even makes it impossible to obtain high quality sp2-BN on SiC. Our results show that successful deposition of epitaxial r-BN is confined to a narrow process parameters window: T = 1500 °C, nitrogen-to-boron ratio of 600-700, hydrogen as carrier gas at a process pressure of 70-100 mbar [2]. In addition, we found that presence of a few parts per million (ppm) of Si is needed for the epitaxial growth of r-BN on sapphire [3] and that it improves quality of the sp2-BN on the SiC substrate.

[1] M. Chubarov, H. Pedersen, H. Högberg, V. Darakchieva, J. Jensen, Per O. Å. Persson, A. Henry,Phys. Stat. Sol. RRL5 (2011), 397

[2] M. Chubarov, H. Pedersen, H. Högberg, J. Jensen, A. Henry, Cryst. Growth Des.12 (2012), 3215

[3] M. Chubarov, H. Pedersen, H. Högberg, A. Henry, CrystEngComm15 (2013), 455

Time Period ThM Sessions | Abstract Timeline | Topic B Sessions | Time Periods | Topics | ICMCTF2014 Schedule