ICMCTF 2025 Session PP2-2-WeA: HiPIMS, Pulsed Plasmas and Energetic Deposition II

High-power impulse magnetron sputtering (HiPIMS) is a physical vapor deposition (PVD) technique in which short pulses of high instantaneous power are applied to a magnetron cathode to significantly increase the degree of ionization of the film-forming material. This generally results in an improved coating quality including reduced surface roughness, increased density, and increased coverage on complex 3D geometries. In addition, reactive HiPIMS has also been shown to display a reduced hysteresis behavior compared to reactive DC magnetron sputtering. If we can properly control the internal process parameters, this will likely have a great impact on the way compound coatings are being deposited, since it allows for stable operation in the desired transition zone and consequently a dramatically increased deposition rate, while still preserving other inherent advantages of HiPIMS.

In this work we take the first steps towards a more detailed understanding of the reactive HiPIMS process by introducing a novel reactive ionization region model (R-IRM). The R-IRM is based on the established ionization region model (IRM), which has been extended to incorporate an extensive nitrogen reaction set together with all the additional complexities arising from the addition of a reactive gas. We use the R-IRM to study the internal process parameters of reactive HiPIMS discharges that are difficult to investigate experimentally by applying the model to a set of HiPIMS discharges of Ti in various Ar/N₂ mixtures and with different external process parameters. The temporal evolution of the densities of the different plasma species, their fluxes towards the substrate, as well as the ionization and back-attraction probabilities obtained from the model give valuable insights into how key properties influencing film growth, such as the material flux composition and charge state of film-forming ions, are affected by the choice of the external process parameters. We furthermore observe, that with the small relative flow rates of N₂ typically needed to obtain stoichiometric coatings, nitrogen only plays a minor role in the plasma chemistry.

Understanding surface bond structures and how they affect material properties is crucial for optimizing the optical and functional qualities of thin films for decorative and functional applications. Specifically, the objective of this research is to investigate the reasons behind color changes and physical property differences among coatings based on metal carbonitrides. We tested samples obtained by High-Power Impulse Magnetron Sputtering (HiPIMS) and Advanced Controlled Arc (ACA), two advanced techniques frequently used to deposit this type of coatings.

In order to investigate both chemical and structural issues, several analytical techniques will be employed. The bonding structures and the chemical composition of the coatings will be characterized by Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). By combining high-resolution Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS), we will be able to thoroughly analyze both surface and cross-sectional morphologies, giving us important insights on the compositional uniformity and microstructural integrity of the films. Additionally, mechanical performance will be studied by nanoindentation to evaluate hardness and scratch tests to assess adhesive strength. The exact color values in the CIE L* a* b* color space are measured using a colorimeter on the samples right after each batch.

By determining the parameters influencing these differences, we seek to improve the knowledge of the process-structure-properties relation in metal carbonitride films. The study's findings are expected to provide useful insights into the customisation of optical and mechanical properties in industrial applications that require precise control over both the appearance and performance of thin films.

High-power impulse magnetron sputtering (HiPIMS) is an advanced technique for thin film deposition, delivering high target power in short pulses to achieve greater ionization than conventional DC magnetron sputtering. Despite this increase in ionization, many ions still have relatively low energy, so substrate biasing is often used to boost energy transfer to the growing film. For insulating substrates, where direct biasing is impossible, bipolar HiPIMS (alternating negative and positive pulses with a floating substrate) offers a partial solution. However, rapid charging of insulated substrates limits energy transfer. This study aims to optimize bipolar HiPIMS pulse configurations to explore the potential enhancement of energy transfer even for insulating substrates.

Experiments were conducted using a magnetron and a Ti target powered by a DC source and driven by a bipolar HiPIMS pulsing unit. Various pulse configurations (unipolar HiPIMS, bipolar HiPIMS, chopped unipolar, and chopped bipolar HiPIMS) were applied under unbalanced magnetic fields (Fig. 1) with the same average power. In-situ ion mass and energy spectroscopy (MS) analyses were carried out, and the total energy flux to a substrate was measured using a passive thermal probe at a floating and ground potential. Moreover, the depositions on insulating substrates or films with various capacitances were simulated by connecting a defined external capacitor between the probe and the ground. Finally, Ti films were deposited on a floating substrate holder for structural analysis.

Unlike standard HiPIMS, bipolar HiPIMS introduces a high-energy peak in the IEDF; with multi-pulse configurations, this peak broadens and the high-energy tail is enhanced. Additionally, time-resolved measurements provide valuable insights, like the evolution of energetic ion flux to the film. Both MS and thermal probe measurements show enhancement of ion and energy fluxes to the substrate for chopped configurations (Fig. 2). Moreover, heat flux varies with capacitance: with a low capacitance, ion acceleration occurs only at the start of each positive pulse before the film surface is fully charged, so the effect on the energy delivered to the film is small. With a high capacitance, ion acceleration is effective throughout the positive pulse regardless of its length, as is the case for a grounded substrate. For medium capacitance, chopping the positive pulse boosts the energy delivered to the film as the substrate discharges during pulse pauses. These effects were also manifested in the structure and stress of the deposited films.

Reactive sputtering of dielectric films poses significant challenges, primarily due to target poisoning, which can lead to arcing, hysteresis, and generally lower deposition rates [1]. RF (radio-frequency, 13.56 MHz) is a stable option for arc-free processes, even though the films can be porous and grow at lower rates than in DC or MF (mid-frequency) mode. HiPIMS (high power impulse magnetron sputtering) is known to deposit dense films, however the tendency for arcing is higher due to the high peak voltages [1].

To provide stable deposition conditions, a hybrid sputtering process is investigated where HiPIMS and RF are simultaneously applied to the same cathode. For this purpose, a Melec SPIK3000A HiPIMS generator is connected alongside an RF generator and a conventional matchbox to the magnetron. An additional filter (Aurion Anlagentechnik GmbH) is necessary to avoid RF reflection into the HiPIMS generator. The radio-frequency can be either applied continuously or by superposition in the on or off-time of the HiPIMS pulses. The film deposition experiments are complemented by plasma diagnostics with energy-resolved mass spectrometry [2] and so-called non-conventional diagnostics as the passive thermal probe [3].

The addition of an RF plasma provides pre-ionization for the HiPIMS pulses, yields to a faster HiPIMS current rise and allows to reduce the process pressure. This phenomenon was already investigated for the superposition of HiPIMS with DC [4] or MF [5]. During reactive sputtering of Al₂O₃ and SiO₂, the addition of RF substantially mitigates arcing, as evidenced by the resulting films, which show a remarkable decrease in droplet density. The deposition rates of the HiPIMS and RF power add up in the superimposed process achieving a higher overall deposition rate.

Proof of principle for a combination of RF and HiPIMS excitation on one magnetron has been established and opens up a new route for arc-free deposition of Al₂O₃ and other oxidic layers. Further investigations will include the influence and optimization of pulse parameters as well as the effect of the ratio between the average HiPIMS and RF power.

[1] A. Anders, J. Appl. Phys. 121, 171101 (2017).

[2] J. Benedikt et al., J. Phys. D: Appl. Phys. 45 (2012) 403001.

[3] H. Kersten et al., Thin Solid Films 377–378 (2000) 585–591.

[4] P. Vašina et al., Plasma Sources Sci. Technol. 16 (2007) 501–510.

[5] W. Diyatmika et al., Surf. Coat. Technol. 352 (2018) 680–689

MAX phases are a unique class of nanolaminated compounds that combine properties of metals and ceramics, offering electrical and thermal conductivity alongside creep, oxidation, and corrosion resistance. Consequently, there is growing interest in synthesizing relatively phase pure MAX phase PVD coatings for a broad range of applications. However, the successful development of MAX-based coatings for next-generation technologies requires a comprehensive understanding of the relationships between the deposition processes, chemical composition and phase formation. Among the various MAX phases, the thin film synthesis of the Ti-Si-C system has been the focus of research for quite some time [1], [2]. Yet, reducing the synthesis temperature to below 650 °C remains a major challenge, as it limits compatibility with metallic substrates and therefore practical use. Regarding this issue, cathodic arc evaporation has great potential due to its elevated ionization degree.

Thus, a variety of Ti-Si-C coatings have been grown by arc evaporating metallic targets (Ti or TiSi) in reactive plasma atmospheres (Ar, SiH₄ & C₂H₂ or Ar & C₂H₂) at 550 °C in an industrial coating plant. To improve adhesion to metallic substrates and to prevent element diffusion between the coating and the substrate, a thin Ti interlayer was applied. The first challenge was the adjustment of the reactive gas flow rates in order to maintain the narrow stoichiometric window during film growth and ensure the formation of Ti-C and Si nanolayers. Final confirmation of the selected deposition approaches was provided by the precise determination of elemental composition using elastic recoil detection analysis (ERDA) and Rutherford backscattering spectrometry (RBS). Subsequently, the focus was on the phase characterization of the Ti-Si-C MAX phases and its most competitive phases (e.g. TiC and Ti₅Si₃C) through various laboratory and synchrotron X-ray diffraction (XRD) techniques, such as BBXRD, GIXRD, HT-GIXRD and CSnanoXRD. In particular, the high energy X-rays used for transmission nanodiffraction experiments allowed accurate phase identification and provided valuable insights into preferred growth directions. Overall, it has been successfully demonstrated for the first time that Ti-Si-C MAX-based coatings can be synthesized by reactive CAE at temperatures below 650 °C.

[1] J.-P. Palmquist et al., “Magnetron sputtered epitaxial single-phase Ti3SiC2 thin films,” Appl. Phys. Lett., vol. 81, no. 5, pp. 835–837, Jul. 2002.

[2]J. Alami et al., “High-power impulse magnetron sputtering of Ti–Si–C thin films from a Ti3SiC2 compound target,” Thin Solid Films, vol. 515, no. 4, pp. 1731–1736, Dec. 2006.

Plasmonic materials require very high temperatures to manufacture and are not available by conventional methods, this study develops a low temperature process to satisfy this demand.

Typically, plasmonic Titanium Nitride thin films produced via PVD methods are deposited at temperatures between 600-800 °C. The Titanium Nitride films produced for this study were deposited at room temperature, ensuring they are CMOS-compatible and consequently, reducing the energy consumption of the process. Titanium Nitride thin films are ideal for real-world applications, due to their high hardness and corrosive resistance, extending the lifetime of components the films are applied to. This study aims to produce films for photocatalytic applications with longer lifetimes than currently produced photocatalytic materials such as nanoparticles.

Among hard coatings materials, transition metal nitrides proved to be valuable candidates with excellent mechanical properties and both chemical and thermal stabilities. This study proposes to show the interest of Reactive High-Power Impulse Magnetron Sputtering (R-HiPIMS) process to produce Vanadium nitride thin films. Thanks to a high ionization degree of the sputtered metal and to high peak power densities applied to the target during few tens of microseconds pulse, deposited films are dense and homogeneous. The influence of several process parameters (target peak power density, N₂ partial pressure, total gas (Ar + N₂) pressure and pulse parameters) on film microstructure are reported. The obtained structures were investigated by X-ray diffraction (GIXRD and θ-2θ) and both scanning and transmission electron microscopy. Discharge composition and electrical characteristics according to processing parameters were studied by optical emission spectroscopy and Langmuir probe measurements. The VN obtained microstructure depends strongly on processing parameters especially pulse parameters and gas parameters which affect the incoming species energy at the substrate. The VN microstructure formation is discussed with respect to conditions promoting both adatoms mobility on the substrate surface and ionized species into the plasma. Comparison of mechanisms involved during the formation of the microstructure depending on the process parameters is presented as well as characterization of mechanical properties (mechanical and electrical) of deposited layers.