Papers

ICMCTF2008 Session H2: High Power Impulse Magnetron Sputtering - HIPIMS 2008

Friday, May 2, 2008 8:00 AM in Room Terrace Pavilion

Friday Morning

Start	Invited?	Item
8:00 AM		H2-1 Investigation of HPPMS in Unipolar, Bipolar, and DC-Superimposed Mode R. Bandorf, M. Vergoehl, P. Giesel, S. Falkenau (Fraunhofer Institute for Surface Engineering and Thin Films IST, Germany); T. Wallendorf (IFU GmbH, Germany); G. Mark (Melec GmbH, Germany) With increasing interest in High Power Pulsed Magnetron Sputtering (HPPMS), processes for several applications are developed. This paper will focus on different pulse modes like unipolar, bipolar, DC-superimposed for high power pulsing. Investigated materials were Titanium, Titania, Nickel Chromium, and Carbon. For unipolar and DC-superimposed mode examples of the modification of the film morphology, the crystal structure, and the density will be shown. Using the DC-superimposed HPPMS it was found that the crystal size increased with increasing DC-fraction, while the largest crystals occurred for the pure DC films. The film density was increased from 8.3g/cm³ for pure DC to 8.5g/cm³ for DC-superimposed HPPMS. For bipolar mode the modifications of Titania films will be discussed. With decreasing duty cycle the roughness of the films decreased. For the Titania films the refractive index and the modification of the film density was investigated. The highest refractive index was realized with bipolar HPPMS. Also the deposition rate of Titania films in the oxid mode of DC-superimposed HPPMS exceeded the sum of the depoition rates of pure DC and pure unipolar HPPMS. Also a redesign of the sputtering cathodes was necessary. For all the experiments with commercial cathodes with a field of 20 - 30mT it turned out that for Carbon sputtering the maximum voltage of the pulse generator was limiting the process. With new low impedance cathodes a significant increase of peak power was realized for Carbon films due to the decrease in discharge voltage. For Nickel-Chromium films a saturation of the discharge current was observed for the commercial cathodes. With the improved low impedance cathodes the peak power and the peak current was significantly increased. For the same duty cycle the peak power was increased by factor of 1.5 only due to the exchange of the cathodes. Further increase of the peak current was realized with modification of the duty cycle whereas before the maximum for the process was reached. Time resolved optical emission spectroscopy (OES) investigations of the HPPMS discharge were carried out to investigate the ions to neutrals ratio to the different cathodes and pulse modes.
8:40 AM		H2-2 Deposition and Characterisation of Industrial Scale, Low Temperature Me-DLC and C-DLC Thin Films Produced by a Combined HIPIMS / Unbalanced Magnetron Sputtering (UBM) Technique L.A. Donohue, Y. Yamazaki (Richter Precision Inc.); S. Kunkel, M. Schenkel, T. Zufrass, W.-D. Münz (SVS Vacuum Coating Technologies, Germany) Carbon coatings find increasing industrial acceptance in automotive, aerospace and medical applications due to low friction and wear coefficient. Recently HIPIMS sources have been shown to produce high ion fraction fluxes with metal content similar to arc sources, without showing excessive heating and droplet formation characteristics. We report on low temperature deposition and characterization of titanium containing (Me-DLC) and metal free (graphite based) DLC films deposited at industrial scale. Before deposition, the coating-substrate interface was engineered using a CFUBM enhanced Ar etch followed by metal ion etch using a Cr HIPIMS source. Variation of substrate bias voltage (600-1000V), pressure (1.8x10^-3mbar to 3.6x10^-3mbar) and duty cycle during HIPIMS etching of steel substrates has been examined by XTEM & EDX. During UBM deposition, magnetic lifting arrays and a central anode could be additionally used to control metal flux rates at the substrate. Mechanical/tribological and physical properties of the Me-DLC and C-DLC coatings have been investigated using XTEM, dynamic micro-hardness, Scratch and Rockwell-C Adhesion, Raman microscopy and pin-on-disc tribological testing. 3.5µm Ti-DLC films showed hardness around 2000HV, friction coefficient 0.1 and excellent adhesion. 2µm thick C-DLC coatings exhibited a cleaner chamber condition than Me-DLC coatings due to much lower C₂H₂ flow usage, significantly increased hardness, low friction coefficient, a shift in phase composition whilst maintaining good adhesion following HIPIMS etch. XTEM analysis across the coating-substrate interface showed distinct modification of the substrate through the use of a HIPIMS source.
9:00 AM		H2-3 Ionized-PVD with HIPIMS - Industrial Potentials and Scientific Challenges U. Helmersson (Linköping University, Sweden) The use of an ionized deposition flux opens for several improvements in the magnetron sputter deposition process in view of guiding and aligning the deposition flux as well as in the use of “self” ion bombardment during substrate cleaning, film nucleation, and film growth. With high power impulse magnetron sputtering (HIPIMS) a high degree of ionization of the sputtered species are achieved and acceleration in the plasma, also without a substrate bias, result in an energy considerable higher than observed for the deposition species during conventionally sputter deposition. For example, about 50 % of the sputtered Ti has an energy higher than 20 eV. This has consequences for the film nucleation and growth. The industrial relevance of the technique is demonstrated by hysteresis free reactive growth of α-Al₂O₃ at low temperatures and by the growth of dense TiN films at room temperature without the use of a substrate bias. Pulsing a plasma process of course increase the complexity and it is more difficult achieving a thorough understanding and to simulate and predict processes. Efforts in this direction will be reviewed and discussed.
9:40 AM		H2-5 Mechanical and Tribological Properties of TiN Films Prepared by HIPIMS J. Paulitsch (Materials Center Leoben Forschung GmbH, Austria); P.H. Mayrhofer (Montanuniversität Leoben, Austria); M. Schenkel, W.-D. Münz (SVS Vacuum Coating Technologies, Germany) TiN coatings are known for their high hardness and good wear resistance. Many research activities concentrate on the correlation between plasma conditions and microstructure and resulting properties of TiN. Here, especially the energy of the film forming species and the energy and density of bombarding ions have a strong influence on the density, texture development, and properties of the resulting films. Generally the density and the mechanical properties of coatings can be improved by increasing the energy and the density of ions in the plasma. The high power impulse magnetron sputtering (HIPIMS) process is known to allow high ion densities in the plasma. Here we show primary results on structure, mechanical and tribological properties of TiN coatings deposited by the HIPIMS technique, which is also used for the substrate-coating interfacial engineering. Hardness values are obtained by an ultra micro indentation system nanoindenter. Investigations on the film adhesion are obtained by Rockwell indentation tests and with scratch tests. The sliding wear resistance is carried out with a ball on disk tribometer. The wear track is evaluated by optical profilometry. The evaluation of the abrasive wear resistance is obtained by the ball-cratering technique. Structural and phase analyses of the HIPIMS grown TiN coatings are conducted by scanning electron microscopy and X-ray diffraction. Details on the interface regions are carried out by transmission electron microscopy. Our results on TiN deposited films clearly demonstrate that HIPIMS is an innovative process not only for interfacial engineering but also for the deposition itself with a wide range of capabilities.
10:00 AM		H2-6 Modulated Pulse Power Deposition of Carbon, Chromium, Carbon Nitride and Chromium Nitride Coatings R. Chistyakov, B. Abraham (Zond, Inc.); W.D. Sproul (Reactive Sputtering, Inc.); J.J. Moore, J. Lin (Colorado School of Mines) Modulated pulse power (MPP) sputtering is a variation of high power pulse magnetron sputtering that overcomes the rate loss issue through modulation of the pulse shape, intensity, and duration. MPP uses a two-step pulse to create highly ionized plasmas. The first step creates a weakly ionized plasma, and once it is stable the cathode voltage is modulated with an increase of this voltage, resulting in the generation of a strongly ionized plasma. Total pulse time is typically 1-3 milliseconds. The pulse shape and duration and plasma perturbations directly affect the degree of ionization of the sputtered material. In this study, C, Cr and reactive CN_x and CrN films were deposited with the modulated pulse power sputtering approach. The applied voltage pulse shape to the magnetron generated a high power pulse discharge and directly affected the degree of ionization of the sputtered material. Nanometer scale layers of C and reactive CN_x and Cr and reactive CrN films were alternately deposited, and the thickness and structure of each nanolayer was controlled by varying the output voltage pulse shape of the MPP plasma generator. The film structure, orientation, and mechanical properties were analyzed and measured. The results of the film property measurements will be presented.
10:20 AM		H2-7 Properties of (Al,Cr)N and (Al,Cr,Si)N Coatings for Cutting Tools in Demanding Cutting Operations Deposited by HPPMS K. Bobzin (RWTH Aachen University, Germany); R. Cremer, J. Alami (CemeCon AG, Germany); N. Bagcivan, P. Immich, S. Bolz (RWTH Aachen University, Germany) Hard coatings with high oxidation resistance and thermal stability are used for economical machining. In this regard nanostructured (Al,Cr)N and nc-(Al,Cr)N/a-Si₃N₄ films were sputtered on tungsten carbide tools and WC/Co samples by using the HPPMS (High Power Pulse Magnetron Sputtering) technology. The relationship between coating composition, microstructure and applied properties was investigated by using X-ray diffraction, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and nanoindentation. The maximum hardness value was about 40 GPa. For both coatings the Al-content was varied from 50 - 75 at% while the silicon content was between 2 - 8 at% for the (Al,Cr,Si)N. In dependence of the silicon content the grain size varied in a range from 3 - 10 nm. As this study focuses on the oxidation behavior of the deposited coatings, annealing tests were carried out in air at temperatures up to 1200 °C. Furthermore SEM pictures of the cross section have been taken around the cutting edge to determine the deposition rate and the film growth. The coatings morphology has been compared to m. f. (middle frequency)- and d. c. (direct current)-sputtered nanocomposite (Al,Cr,Si)N films indicating enhanced properties due to the application of the HPPMS-technology with regard to denser structure, higher hardness, higher oxidation stability, smoother surface and better thickness uniformity.
10:40 AM		H2-8 Influence of Discharge Current and Target Material on the Ion Energy and Composition of HIPIMS Plasmas Near the Substrate A.P. Ehiassian, A. Vetushka (Sheffield Hallam University, United Kingdom); S. Konstantinidis (Université de Mons-Hainaut, Belgium) High power impulse magnetron sputtering (HIPIMS) plasmas are characterised with a high degree of ionisation of the target material. However, the plasma composition near the substrate has not been studied in detail. In this study we show that the plasmas generated during HIPIMS of Ti and Cr are strongly affected by discharge current, Id and the target material. Langmuir probe measurements of the plasma density showed a linear increase from 1 to 6 x 10¹¹ cm^-3 with Id increasing from 0.4 to 1.8 Acm^-2. The metal ion-to-metal neutral ratio Me¹⁺ : Me⁰ increased significantly from 0.5 to 1 as shown with atomic absorption spectroscopy. At the same time, the Ar ion to metal ion ratio Ar¹⁺ : Me¹⁺ increased strongly at low currents below 1 Acm^-2 and saturated to 2.5 at currents above this value. The ion energy distribution functions measured with energy-resolved mass spectroscopy showed that a high energy tail becomes more dominant as Id is increased. In general this confirmed that the metal ion content in the plasma increases with discharge current. A greater metal ion content accompanied with a higher plasma density were associated with materials with greater sputter yield. The mechanisms governing the ionisation of metal and its diffusion to the substrate are discussed.