High performance pulsed magnetron sputtering

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The Hochenergieimpulsmagnetronsputtern ( English high power impulse magnetron sputtering , HiPIMS, or high power pulsed magnetron sputtering , HPPMS) is a special magnetron sputtering for the deposition of thin films .

HiPIMS uses very high target power densities of a few kW · cm −2 in short pulses of a few tens of microseconds with a low duty cycle (on-off ratio) of less than 10%. A characteristic feature of the HiPIMS is the high degree of ionization of the sputtered donor material and the high rate of molecular gas dissociation . In the conventional DC sputtering process , a higher ionization of the deposited target material can be achieved by increasing the cathode power. Limits result from the higher thermal load on the cathodes and the substrates to be coated . This is where HiPIMS comes in: Since the pulses only act on the target material for a very short time and are followed by a relatively long “off time”, the average cathode power is low (1–10 kW). In this way, the target material can cool down during the off times and the process is stable.

HiPIMS plasma discharge

Scheme of the magnetron sputtering process

HiPIMS plasma is generated by a glow discharge , whereby the current density of the discharge can reach up to 6 A · cm −2 , while the discharge voltage is kept constant at a few hundred volts. The discharge is distributed homogeneously on the cathode surface of the chamber. HiPIMS generates a high plasma density of 10 13 ions per cubic centimeter, which contain high proportions of target metal ions. The main ionization mechanism is electron impact, which is balanced by charge exchange and diffusion. The ionization rates depend on the plasma density.

The degree of ionization of the metal vapor is a decisive function of the peak current density of the discharge. At high current densities, sputtered ions can be ionized up to 5 times with a charge. The formation of target ions with simple ionization is responsible for a possible secondary electron emission , which has a higher emission coefficient than the kinetic secondary emission in conventional glow discharges. The generation of possible secondary electron emission can improve the current of the discharge.

HiPIMS is typically operated in short pulse mode (impulses) with a low pulse duty factor in order to avoid overheating of the target and other system components. With each pulse, the discharge goes through several phases:

  • Electric breakdown
  • Gas plasma
  • Metal plasma
  • Stable phase that can be reached when the density of the metal plasma is high enough to effectively dominate the gas plasma.

A negative voltage (bias voltage) applied to the substrate influences the energy and direction of movement of the positively charged particles hitting the substrate. Since the pulses only act on the target material for a very short time in the range of a few hundred microseconds (1 microsecond = 1 millionth of a second) and this is followed by a relatively long “off time”, the average cathode power is low (1–10 kW ). In this way, the target can cool down during the off times and the process is stable.

The discharge maintained by the HiPIMS is a high-current glow discharge that is transient or quasi-stationary . Each pulse remains as a glow until a certain point in time, after which it changes into an arc discharge . If the pulse length is kept below this certain period of time, the discharge will continue stably for an indefinite period.

Applications

HiPIMS is used for:

  • the adhesion-improving pretreatment of the substrate before layer deposition (etching of the substrate)
  • Deposition of thin layers with high microstructure density

Substrate pretreatment

Before the deposition of thin layers on mechanical components such as vehicle parts, metal cutting tools or decorative fittings, a substrate pretreatment in a plasma environment is required. The substrates are exposed to a plasma and subjected to a high negative voltage of a few hundred volts. This creates a high-energy ion bombardment that removes any contamination. If the plasma contains metal ions, these can be implanted, that is to say introduced, into the substrate to a depth of a few nanometers (cf. ion implantation ). HiPIMS is used to generate plasma with a high density and a high proportion of metal ions. If you look at the layer / substrate contact surface in cross section, you can see a clean contact surface. Epitaxial or atomic layers typically lie between the crystal of a nitride layer and the crystal of a metal substrate when HiPIMS is used for pretreatment. HiPIMS was first used by AP Ehiasarian in February 2001 for the pre-treatment of steel substrates.

Substrate bias during pretreatment requires high voltages which require appropriately developed arc detection and suppression technology. Dedicated DC substrate bias units provide the most versatile option as they maximize substrate etch speeds, minimize substrate damage, and operate in multiple cathode systems. An alternative is to use two HiPIMS power sources that have been synchronized in a master / slave configuration: one to generate the discharge and one to generate a pulsed substrate bias.

Thin film deposition

Thin layers that are deposited by HiPIMS at a discharge current density of greater than 0.5 A · cm −2 have a dense columnar structure with no gaps. The deposition of copper layers by HiPIMS was first reported by V. Kouznetsov; for filling 1 µm vias with an aspect ratio of 1: 1.2.

Chromium nitride thin layers (CrN thin layers) were first deposited by HiPIMS from AP Ehiasarian in February 2001. The examination of these layers using transmission electron microscopy showed a dense microstructure without any major damage. The layers also had a high degree of hardness , good corrosion resistance and a low sliding wear coefficient. These research results paved the way for the first industrial use of the technology in January 2004 at Sheffield Hallam University , Great Britain, in collaboration with Advanced Converters , Warsaw, Poland (now Hüttinger Electronics , Poland). The first HiPIMS coating systems came onto the market in 2006. The commercialization that followed made the technology available to a wider scientific audience and led to further developments in numerous areas. At the AMB 2010, CemeCon AG from Würselen presented HPN 1, the first series coating materials based on the HiPIMS process and has since been offering HiPIMS technology on an industrial scale.

The following materials, among others, were successfully deposited by HiPIMS:

advantages

The joint electron microscopy laboratory (GFE) at RWTH Aachen University offers a wide range of options for material analysis . The picture shows the surface topography and the crystal structure of the HiPIMS coating HPN1 from CemeCon AG, Würselen on a hard metal substrate at 10,000 times magnification in the scanning electron microscope

Advantages of HiPIMS layers are, in particular, a denser layer morphology and an increased ratio of hardness to the E-module of the layer compared to conventional PVD layers. While comparable conventional, nano-structured (Ti, Al) N layers have a hardness of 25 GPa and an elastic modulus of 460 GPa, the hardness of the new HiPIMS layer is over 30 GPa with an elastic modulus of 368 GPa. The ratio of hardness and modulus of elasticity is a measure of the toughness properties of the layer. A high degree of hardness with a relatively small modulus of elasticity is beneficial, as is the case with the HiPIMS layer. In addition to the denser layer structure, a completely new material composition is responsible for the extremely high thermal stability of the HiPIMS layer. In addition, the coating process enables the layer adhesion to be doubled compared to previous layers. This is an advantage when working with sharp cutting edges in an interrupted cut, for example with superalloys . HiPIMS layers on cutting tools are able to process difficult-to-cut materials, such as nickel-based alloys and stainless austenitic steels, more economically - with significantly increased cutting parameters and much less tool wear.

Further information

Web links

Individual evidence

  1. ↑ a b Werner Kölker: Hand in hand with research and development. In: CemeCon Facts. No. 36, pp. 10–11 ( cemecon.de  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. PDF).@1@ 2Template: Dead Link / www.cemecon.de  
  2. ↑ a b c Arutiun P. Ehiasarian, R. New, W.-D. Munz, L. Hultman, U. Helmersson, V. Kouznetsov: Influence of High Power Densities on the Composition of Pulsed Magnetron Plasmas . In: Vacuum . 65, No. 2, 2002, pp. 147-154. doi : 10.1016 / S0042-207X (01) 00475-4 .
  3. ↑ Werner Kölker: More design freedom in the layered construction. In: CemeCon Facts No. 36, pp. 14–15 ( cemecon.de  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. PDF ).@1@ 2Template: Dead Link / www.cemecon.de  
  4. ↑ Arutiun P. Ehiasarian, JG Wen, I. Petrov: Interface microstructure engineering by high power impulse magnetron sputtering for the enhancement of adhesion . In: Journal of Applied Physics . 101, No. 5, 2007, S. item 054301, 10 pp .. doi : 10.1063 / 1.2697052 .
  5. ↑ a b E. Broitman, Czigány, Zs .; Greczynski, Greczynski, G; Böhlmark, J; Cremer, R .; Hultman, L .: Industrial-scale deposition of highly adherent CNx films on steel substrates . In: Elsevier (Ed.): Surface and Coatings Technology . 204, No. 21-22, 2010, pp. 3349-33576. doi : 10.1016 / j.surfcoat.2010.03.038 .
  6. ↑ V. Kouznetsov, K. Macak, J. Schneider, U. Helmersson, I. Petrov: A novel pulsed magnetron sputter technique Utilizing very high target power densities . In: Surface and Coatings Technology . 122, No. 2-3, 1999, pp. 290-293. doi : 10.1016 / S0257-8972 (99) 00292-3 .
  7. ↑ Patent US6296742 : Method and apparatus for magnetically enhanced sputtering. (Priority date December 9, 1997). ‌
  8. ↑ a b Arutiun P. Ehiasarian, W.-D. Munz, L. Hultman, U. Helmersson, I. Petrov: High Power Pulsed Magnetron Sputtered CrNx Films . In: Surface and Coatings Technology . 163-164, 2003, pp. 267-272. doi : 10.1016 / S0257-8972 (02) 00479-6 .
  9. ↑ AP Ehiasarian, Bugyi, R .: Industrial size high power impulse magnetron sputtering . In: Society of Vacuum Coaters (Ed.): 47th Ann. Techn. Conf. Proc. Society of Vacuum Coaters . 2004, Dallas, TX, 2004, ISSN  0737-5921 , pp. 486-490.
  10. ^ YP Purandare, Ehiasarian, A ..; Hovsepian, P.Eh.;: Deposition of nanoscale multilayer CrN / NbN physical vapor deposition coatings by high power impulse magnetron sputtering . In: AVS (Ed.): J. Vacuum Sci. Technol. A . 26, No. 2, 2008, pp. 288-296. doi : 10.1116 / 1.2839855 .
  11. ↑ P. Eh Hovsepian, Reinhard, C.; Ehiasarian, AP ;: CrAlYN / CrN superlattice coatings deposited by the combined high power impulse magnetron sputtering / unbalanced magnetron sputtering technique . In: Elsevier (ed.): Surf. Coat. Technol. . 201, No. 7, 2006, pp. 4105-10. doi : 10.1016 / j.surfcoat.2006.08.027 .
  12. ↑ S. Konstantinidis, JP Dauchot, M. Hecq: Titanium oxide thin films deposited by high-power impulse magnetron sputtering . In: Thin Solid Films . 515, No. 3, 2006, pp. 1182-1186. doi : 10.1016 / j.tsf.2006.07.089 .
  13. ↑ S. Konstantinidis, A. Hemberg, JP Dauchot, M. Hecq: Deposition of zinc oxide layers by high-power impulse magnetron sputtering . In: J. Vac. Sci. Technol. B . 25, No. 3, pp. L19-L21. doi : 10.1116 / 1.2735968 .
  14. ^ V. Sittinger, F. Ruske, W. Werner, C. Jacobs, B. Szyszka, DJ Christie: High power pulsed magnetron sputtering of transparent conducting oxides . In: Thin Solid Films . 516, No. 17, 2008, pp. 5847-5859. doi : 10.1016 / j.tsf.2007.10.031 .
  15. ↑ J. Alami, P. Eklund, J. Emmerlich, O. Wilhelmsson, U. Jansson, H. Högberg, L. Hultman, and U. Helmersson: High-power impulse magnetron sputtering of Ti – Si – C thin films from a Ti3SiC2 compound target . In: Elsevier BV (Ed.): Thin Solid Films . 515, No. 4, December 5, 2006, pp. 1731-1736. doi : 10.1016 / j.tsf.2006.06.015 .
  16. ↑ Stephan Bolz: New coating technology achieves best adhesion. In: CemeCon Facts No. 35, pp. 14–15 ( cemecon.de  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. PDF ).@1@ 2Template: Dead Link / www.cemecon.de