ICMCTF2012 Session B2-2: CVD Coatings and Technologies

Thursday, April 26, 2012 1:30 PM in Room Royal Palm 4-6

Thursday Afternoon

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1:30 PM B2-2-1 CVD – Opportunities and Challenges
Helga Holzschuh (SuCoTec AG, Switzerland)

Although the Chemical Vapor Deposition (CVD) technique is 160 years old there are still opportunities and challenges. The tool manufacturing industries have generated a growing demand for novel material applicable for large scale production.

Due to advances in CVD technology the transfer of new coating materials from lab scale to production size is made possible. These advances allow us to question results generated in the last decades of CVD. They will give rise for better understanding of the CVD processes and consequentially it will give new chances for novel coatings.

Because of its large application potential the main focus of this work will be on hard materials. A review of state of the art coatings and post treatments in tool manufacturing industries will be given. But what will be the next challenges for CVD?

2:10 PM B2-2-3 SiC coatings grown by liquid injection chemical vapor deposition using single source metalorganic precursors.
Guillaume Boisselier, Francis Maury (CIRIMAT, France); Frédéric Schuster (CEA, France)
Silicon carbide is an attractive material used for instance as protective ceramic coating or as functional layer in electronic devices. As a result, there is a great interest for growth processes aiming low temperatures, high deposition rates, large-scale capacity, and other constraints imposed by the application. To meet such requirements, SiC coatings have been grown in a horizontal hot wall chemical vapor deposition reactor assisted by pulsed direct liquid injection (DLI-CVD) using metalorganic compounds as single sources. Commercial 1,3-disilabutane and polycarbosilane were used as 1:1 Si:C liquid precursors. Amorphous and stoichiometric SiC coatings were deposited on various substrates in the temperature range 650- 750 °C and under a total pressure of 5-50 Torr. Thickness gradients due to the temperature profiles and the precursor depletion were observed in the reactor axis but the thickness uniformity can be improved as a function of the deposition conditions. Growth rates as high as 90 µm/h were obtained using pure precursors. The injection of toluene solutions significantly reduces the deposition rate and allows a better control of the growth rates and of the microstructure of coatings. In that case, they exhibit a smooth surface morphology and a very dense structure. Under the explored conditions (reactor temperature and dewelling time of reactive species) the decomposition rate of toluene was found negligible. As a result, the presence of solvent vapor in the CVD reactor is not a source of carbon contamination for the SiC coatings that keep the 1:1 stoichiometry. The influence of the substrate temperature, the solvent and the nature of precursor used in this DLI-CVD process is discussed and preliminary properties are presented.
2:30 PM B2-2-4 Multilayer Diamond Coatings: Theory, Implementation in Production and Results in different Applications
Christian Bareiss, Werner Koelker, Christoph Schiffers, Manfred Weigand, Oliver Lemmer (CemeCon AG, Germany)

Since many years diamond coatings are a well established technique to enhance the lifetime of cemented carbide tools in the machining of extremely abrasive materials like graphite, carbon fibre reinforced plastics (CFRP) and some aluminum alloys. The main advantage of crystalline diamond films in machining applications is their outstanding hardness and durability, but these properties also come along with an enormous brittleness of diamond coatings. So for further improvement of the coating and tool lifetime, we have to understand first the different failure mechanisms, which may lead to damages and delaminations of the diamond coating. Typical damages in diamond coatings during machining are the formation of small cracks in the film, which may expand along the grain boundaries and cause film delamination in large areas according to the brittleness of diamond.

The CemeCon AG developed Multilayer CVD diamond coatings to combine the unique durability of diamond coatings on cemented carbide tools in machining performances with an enhanced tolerance to small cracks and damages in the diamond film without catastrophic failure. These multilayer diamond coatings are alternating layers of tough micro-crystalline and smooth nano-crystalline films. The achieved difference in crystal size between these two types enables a homogeneous dissipation of the initial crack energy by continuous change of the crack growth direction as shown in the figure. The implementation of these multilayer coatings in the machining of the most challenging materials like CFRP led to a further tool performance improvement compared to completely micro- or nano-crystalline diamond films.

CemeCon will present the theory of crack growth in these multilayer coatings and some examples of the diamond film performance in industrial applications.

2:50 PM B2-2-5 Adhesion of the DLC film on iron based materials as a function of gradient interlayer properties
Douglas Baquião, Guilherme Faria, Luiz Silva Junior (Institute for Space Research, Brazil); Luis Bonetti (Clorovale Diamantes S.A., Brazil); Evaldo Corat, Vladimir Trava-Airoldi (Institute for Space Research, Brazil)
Diamond-like Carbon (DLC) films have attracted considerable interest over due to their high hardness, low friction coefficient, high wear resistance, high thermal conductivity, high elastic modulus, chemical inertness, biocompatibility, and more recently because of the real possibilities of deposition inside of the long iron based tubes for unlimited applications. In this case very adherent DLC films can give to scientific and development areas special opportunities to solve some problems related to transportation of aggressive liquids like petroleum based and other minerals. The major disadvantage of hard DLC film deposition is a relatively low adhesion of these films on iron based substrates. To overcome the low adhesion problems of these films on iron based substrates, different coating concepts have been proposed, normally on high temperature condition, which is not appropriated for iron based material structure. In this work it was proposed an interlayer, obtained at low temperature by using low energy ion implantation, emerging from the bulk of the substrate and overlapping with DLC films. A convenient unique body of substrate-DLC films with mechanical and tribological gradient properties near substrate surface was obtained and related to its higher adhesion, lower stress, and hardness. The interlayer and DLC films at very high growth rate were obtained by using an enhanced asymmetrical bipolar PECVD DC pulsed power supply system. The adhesion and hardness were evaluated by scratching test and nano indentation, respectively. Also, a simulation of the interlayer gradient by using TRIM/SRIM software for low energy ion implantation was obtained with good agreement with experimental data.
3:10 PM B2-2-6 Effect of the carrier gas flow rate on boron-doped diamond synthesis using mode-conversion type microwave plasma CVD
Hikaru Shimomura, Yukihiro Sakamoto (Chiba Institute of Technology, Japan)
Although diamond is well known an electrical insulator with a resistivity of the order of 10^ 16 Ω・ cm, it is changed to the semiconductor by inclusion of the dopant such as boron or phosphorus. Generally, diborane (B2H6) or trimethyl-boron {B(CH3)3} are used as B sources to synthesize boron-doped diamond. However, these dopants are toxic to humans. On the other hand, trimethyl-borate {B(OCH3)3} is safety, against to B2H6 or B(CH3)3. The investigation was carried on the effect of the carrier gas flow rate for the boron-doped diamond synthesis using mode-conversion type microwave plasma CVD.

The boron-doped diamond films were synthesized using mode-conversion type microwave plasma CVD apparatus. The Si substrate was scratched by diamond powder and then cleaned ultrasonically in acetone solution. Reaction gases were used CH4 (15 SCCM) and H2 (100 SCCM). Vapor of B(OCH3)3, the boron source, was carried by H2 carrier gas into the vacuum chamber with its flow rate of 1 to 6 SCCM. Pressure was 20.0kPa and microwave power was 1.0 kW. Reaction time was fixed to 3 h. The surface and cross sectional morphologies of deposits were observed by SEM. Qualities of the deposits were estimated by Raman spectroscopy. Electrical resistivities were measured by the four-point probe method.

As a result of the SEM observation, the grain sizes of deposits were 1 to 3 μm. The maximum thickness of 6 μm was obtained for carrier gas flow rate ; 3 SCCM. From the Raman spectra of the deposits, the broad peak at about 500, 1230 cm^-1 and the weak peak at 1333 cm^ -1 were observed for each samples. These peaks due to including high concentration of boron in the films. In addition, the intensities of the peaks at 1333 cm^ -1 were decreased with increasing of the carrier gas flow rate. As a result of the electrical resistivity measurements by the four-point probe method, the electrical resistivities of boron-doped diamond films decreased with increasing of carrier gas flow rate. The minimum electrical resistivity of 2.5×10^ -1Ω・ cm was obtained for carrier gas flow rate ; 6 SCCM.

As a conclusion, the boron-doped diamond films were fabricated with each carrier gas flow rates. In the Raman spectra of the films, the peaks caused high boron inclusion were observed.

3:30 PM B2-2-7 Low temperature chemical vapor deposition of boron-carbon films for use in neutron detectors
Henrik Pedersen (Linköping University, Sweden); Carina Höglund (European Spallation Source ESS AB/ Linköping University, Sweden); Jens Birch, Jens Jensen, Anne Henry (Linköping University, Sweden)

A novel design for neutron detectors based on the isotope 10B instead of 3He has been suggested by the European Spallation Source (ESS), to overcome the very limited availability of 3He. In the detector design, very large area aluminum blades are coated with a thin film containing high amounts of 10B. 10B4C was chosen as the thin film material instead of pure 10B, since it is easier to handle in a deposition process and due to its high resistance towards oxidation and wear. Here we demonstrate the synthesis of thin, amorphous, boron-carbon films at low temperature (400-600 °C), by thermally activated CVD using the organoborane triethylboron, B(C2H5)3, (TEB) as single precursor. Since the neutron detectors will be based on aluminum, there is an upper temperature limit of approximately 600 °C, which limits a number of possible CVD-processes and also the aluminum substrate prevents the use of BCl3 as boron precursor. Deposition by TEB is done on both single crystalline Si (100) substrates and aluminum plates; the deposition rate at 600 °C was close to 1 µm/h in argon and 0.35 µm/h in hydrogen. The film density, as measured by X-ray reflectivity (XRR), for films deposited at 600 °C in hydrogen was 2.42 g/cm3 (97 % of bulk B4C) and 2.14 g/cm3 (86 % of bulk) for films deposited at 600 °C in argon. The atomic content of the deposited films were analyzed by Time of Flight Elastic Recoil Detection Analysis (ToF-ERDA), films with B/C-ratio of 4.6 and 3.6 were deposited at 600 °C in hydrogen and argon respectively, the hydrogen content in the films was 3-4 at%, regardless of deposition ambient. Both the film composition and film density was found to vary significantly with deposition temperature and deposition ambient. Based on our results, a deposition mechanism for boron-carbon films from TEB, where the TEB molecule is decomposed to BH3 and hydrocarbons, is suggested.

4:10 PM B2-2-9 Effects of ammonia/acetylene mixtures on the properties of carbon films prepared by thermal chemical vapor deposition
Liang-Hsun Lai, Sham-Tsong Shiue (National Chung Hsing University, Taiwan)

When ammonia is added in acetylene to form carbon films using thermal chemical vapor deposition, effects of different ammonia/acetylene ratios on the deposition rate and microstructures of carbon films are investigated. The deposition temperature, working pressure, and deposition time of the thermal CVD process were set to 1113 K, 8 kPa, and 25 min, respectively. The total mass flow rate of acetylene and ammonia were kept at 40 cm3/min, and five kinds of carbon films were prepared with the ammonia/acetylene ratio of 0, 4/36, 8/32, 12/28, 16/24, and 20/20. Experimental results indicate that the deposition rate of carbon films decreases as the ammonia/acetylene ratio increases. The mean crystallite size and ordered degree of carbon films increase with increasing the ammonia/acetylene ratio. Moreover, when the ammonia/acetylene ratio increases, the carbon films have more sp3 carbon atoms and shift to diamond -like. Few nitrogen and hydrogen atoms are incorporated into carbon films. The deposition rate of carbon films is proportional to the partial pressure of acetylene with a power of about eighth order, and thus, the pyrolysis of acetylene with added ammonia is controlled by the adsorption process of sixteen-carbon species on the substrate. The results of thermal CVD carbon deposition using acetylene and ammonia are compared with those using acetylene and nitrogen.

4:30 PM B2-2-10 Hollow-Cathode Deposition of Thin Films Via Metal Hydride Formation and Decomposition
Stephen Muhl (Universidad Nacional Autónoma de México - Instituto de Investigaciones en Materiales, Mexico); Wendi Lopez (IIM-UNAM, Mexico); Ovidio Pena-Rodriguez (Autonomous University of Madrid, Spain)

Approximately 30 to 40 years ago the group of Stan Vepřek of the University of Zurich described that thin films of polycrystalline silicon could be prepared utilizing a reversible chemical reaction. In their paper they described how pieces of silicon were exposed to a low-pressure high-density hydrogen plasma promoting the formation of volatile silicon hydride, this was then transported within the reactor to a hot substrate which caused the decomposition of the hydride and the deposition of the silicon film.

Hydrogen plasmas have also been used for chemical etching of various materials and, for example, in the case of the deposition of diamond films the preferential etching of sp2 bonded carbon is considered to be of fundamental importance.

In this paper we describe the etching of a metal (Mo or Ni) by hydrogen which was plasma-activated in a RF hollow cathode where the water-cooled cylindrical cathode was lined with the appropriate metal. The metal hydride vapour generate in the plasma was directed to quartz substrates which were maintained temperatures in excess of 300 oC. The metal hydride was thermal decomposed and a thin film of the metal was deposited. A special substrate heater was constructed such that four quartz substrates could be simultaneously exposed to the metal hydride vapour, but with each substrate at a different temperature; each approximately 20oC less than the neighbouring one. In this way, depositions under identical conditions could be carried out at the same time but at four different temperatures. We report the deposition rate as a function of the substrate temperature and the RF plasma power applied to the hollow cathode.

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