ICMCTF2015 Session F2-1: High Power Impulse Magnetron Sputtering (HiPIMS)

Two features of high-power pulsed magnetron sputtering (HIPIMS) render this technique particularly attractive for growth of transition metal (TM) nitride alloys: (i) the high ionization degree of the sputtered metal flux, and (ii) the time separation of metal- and gas-ion fluxes incident at the substrate.[1] The former implies that ion fluxes originating from elemental targets operated in HIPIMS are distinctly different from those that are obtained during dc magnetron sputtering (DCMS), which helps to separate the effects of HIPIMS and DCMS metal-ion fluxes on film properties. The latter feature allows one to minimize compressive stress due to gas-ion irradiation, by synchronizing the pulsed substrate bias with the metal-rich-plasma portion of the HIPIMS pulse.

We use pseudobinary TM nitride model systems TiAlN, TiSiN, and TiTaN to carry out experiments in a hybrid configuration with one target powered by HIPIMS, the other operated in DCMS mode. [2],[3] This allows us to probe the roles of intense M₁ⁿ⁺ and M₂ⁿ⁺ metal-ion fluxes (n = 1, 2) from HIPIMS-powered targets on film growth kinetics, microstructure, and physical properties over a wide range of M₁M₂N alloy compositions.

TiAlN and TiSiN mechanical properties are shown to be determined by the average metal-ion momentum transfer per deposited atom <p_d>.[4] Irradiation with lighter metal-ions (M₁ = Al⁺ or Si⁺ during M₁-HIPIMS/Ti-DCMS) yields fully-dense single-phase cubic Ti_1-x(M₁)_xN films. In contrast, with higher-mass film constituent ions such as Ti⁺, <p_d> easily exceeds the threshold for precipitation of second phase w-AlN or Si₃N₄.

VO₂ films have recently attracted much attention in microelectronics and optics due to their ultrafast insulator-to-metal phase transition near room temperature [1, 2]. Other vanadium oxides (V₂O₃ and V₂O₅) also exhibit similar properties either below or above room temperature [3] but VO₂ is believed to be the most promising candidate among these oxides to be utilized for various applications.

VO₂ thin films have been previously grown on various substrates by pulsed laser deposition [1], dc (dcMS) and rf magnetron sputtering [4, 5] and reactive bias target ion beam deposition [2] under various O₂ partial pressures [6] and their electrical properties have been extensively studied [1, 2, 4, 5]. To benefit the impact of the highly ionized plasma on the film properties, we have grown vanadium oxide thin films on c-plane sapphire by high power impulse magnetron sputtering (HiPIMS) and dcMS under different O₂ flows. Prior to the film growth, the average power of the HiPIMS plasma was measured for various O₂ flows and pulse repetition frequencies, and the transition of the vanadium target from metal mode to oxide mode was mapped. The growth rate and plasma stability was also determined for each state of the target.

As the O₂ flow increases from 1 to 6 sccm, X-ray diffraction patterns reveal the transition of the epitaxial films from V₂O₃ through VO₂ to V₂O₅ for both HiPIMS and dcMS processes. The increased O₂ flow results in an additional incorporation of oxygen atoms and ions into the films which induced vacancies and epitaxial degradation for the dcMS grown films while the increased O₂ flow has less impact on the quality of the epi-layers in the HiPIMS process. X-ray reflectivity measurements show that the HiPIMS grown films are denser and smoother compared to the dcMS grown films. Atomic force microscopy measurements reveal that at higher O₂ flows, the surface roughness increases drastically in the dcMS grown films while the HiPIMS grown films demonstrate lower surface roughness for elevated O₂ flows compared to dcMS grown films. Therefore, an O₂ flow interval can be found to obtain stoichiometric VO₂ films for each process. The resistivity of VO₂ films grown by HiPIMS and dcMS processes was also measured as a function of temperature and their insulator-to-metal transitions are compared.

[1] M. Nakano et al., Nature. 487 (2012) 459 - 462.

[2] L. Wang et al., Opt. Lett. 37 (2012) 4335.

[3] A. L. Pergament, ISRN Condens. Matter Phys. (2011) 605913.

[4] E. Kusano et al., J. Vac. Sci. Technol. A, 6 (1988) 3.

[5] A. Zimmers et al., Phys. Rev. Lett. 110 (2013) 056601.

[6] S. Kittiwatanakul et al., J. Appl. Phys. 114 (2013) 053703.

Hydrogenated Si_yN_x (0.06 < x < 0.42) coatings were deposited by reactive high power impulse magnetron sputtering (rHiPIMS) using a pure Si target, NH₃/Ar or NH₃/N₂/Armixtures onto Si and steel substrates. The depositions were carried out in an industrial coating system. During coating deposition the pressure and temperature were kept constant at 400 mPa and 150 °C, respectively. For this study, the NH₃-to-Ar flow ratio, the pulse frequency, and the average target power were varied. The processes as well as the coating properties were also addressed theoretically. Synthetic Growth Concept calculations based on Density Functional Theory were conducted in order to assess the availability and role of precursor species during the rHiPIMS processes in NH₃/Ar and N₂/Armixtures. The Si_yN_x properties were studied by elastic recoil detection analysis, X-ray photoelectron spectroscopy, X-ray diffraction, X-ray reflectivity, and nanoindentation as well as Rockwell C tests in order to investigate the H and N contents of the films, their chemical bonding structure, residual stress, density, and mechanical properties, respectively.

Our theoretical results suggest that 16 different film forming species are prevalent in the Si/NH₃/Ar discharge. Most important species for the film formation were predicted to be dimers such as NH, Si₂, SiH, and SiN, trimers like N₂H and SiNH as well SiNH₂ and N₂H₂ molecules. While the former category of plasma species is highly reactive, trimers and XNH₂ molecules contribute to Si_yN_x film formation not only by their comparatively high amount of dangling bonds, but also by their high cohesive energies, providing cohesive and adhesive strength of the coating. The experimental results show that the reactive Si_yN_x deposition process and film properties are strongly influenced by the NH₃-to-Ar flow ratio, the pulse frequency as well as the average target power. The pulse frequency was found to be a powerful tool to tailor the composition of the Si_yN_x films and thus, their mechanical properties. Consequently, the chemically enhanced rHiPIMS discharge of Si in NH₃/Ar atmosphere suggests an improved control of the thin film properties.

Plasma enhanced magnetron sputtering (PEMS) is an improved version of the DC magnetron sputtering (DCMS) technique by introducing an extra global plasma generated by an electron source, e.g. hot filaments, to enhance the Ar ionization. Deep oscillation magnetron sputtering (DOMS) is a new high power impulse magnetron sputtering (HiPIMS) technique that uses large voltage oscillation packets to achieve high power pulses for sputtering. As compared to conventional DC and pulsed DC magnetron sputtering (PDCMS), the PEMS and DOMS techniques aim at increasing the plasma ionization degree and hence the ion flux, thereby improving the structure and properties of the coating. It is important to understand the characteristics of these processes and their capabilities/limits for coating depositions. In this study, thick TiSiCN nanocomposite coatings were reactively deposited in a closed field unbalanced magnetron sputtering system by sputtering metal Ti targets using DCMS, PDCMS, PEMS, DOMS, or the hybrid of PEMS+DOMS technique in a reactive gas mixture containing argon, nitrogen and trimethylsilane. The PEMS process showed the highest mean substrate current density mainly contributed from low energy Ar ions. The DOMS process showed high peak substrate current density in the pulses mainly contributed from ionized metal target ions with a distribution of ion energies. The deposition rate, ion current density on the substrate, process temperature, and the process stability will be compared. More importantly, the microstructure, residual stress, mechanical and tribological properties of the TiSiCN nanocomposite coatings deposited by these techniques will also be reported.

High power impulse magnetron sputtering (HIPIMS) is a newly developed coating technology, characterized by its ultra-high peak current and peak power density to achieve unique thin film properties, such as high hardness, good adhesion and tribological performance. In this study, a hybrid coating system consisting with high power impulse magnetron sputtering (HIPIMS) and radio frequency (RF) sputtering was used to deposit CrVN coatings with various V contents. The phase of the coatings was analysis by X-ray diffractometer (XRD). The microstructures of thin films were examined by the field-emission scanning electron microscopy (FE-SEM). Atomic force microscopy (AFM) was used to characterize the surface morphology. The nanoindentation was used to evaluate the hardness properties of thin films. The scratch tests, Daimler- Benz Rockwell-C (HRC-DB) adhesion tests and pin-on-disk wear tests were used to evaluate the adhesion and tribological properties of thin films, respectively. Effects of vanadium concentration, duty cycle and pulse frequency of HIPIMS system on the microstructure and mechanical properties of CrVN thin films were discussed in this work.

Despite the tremendous potential of oxide semiconductors, further advancements have been hampered by a lack of hole-transporting (p-type) oxides with similar or comparable transport characteristics to their n-type counter parts. In responding to the diversifying and active field of oxide semiconductor materials recently, the titanium monoxide (TiO) having great potential for thin-film transistor (TFT) is elucidated its optical and electrical properties. In particular, rock-salt type γ-TiO is deposited on an unheated flexible substrate . High power impulse magnetron sputtering (HIPIMS), known to provide high density plasma, was used as the sputter power generator. Substrate bias voltage and thermal annealing effect were evaluated. Experimental results reveal that the as-prepared TiO film obtained very high density. The saturation mobility, the electrical conductivity and the optical transmittance are dependent on the output waveform of the HIPIMS generator. The properties of the TFT device using TiO layer as the channel layer are also explored.

The Super Imposed Pulse Power Technology ( SIPP Technology) offers significant advantages in HiPIMS technology.

The Combination of unipolar pulse HiPIMS plasma with a synchronized DC-plasma using a single magnetron allows a higher deposition rate compared to a conventional HiPIMS pulse sequence only. The influence and the different rise pulse current time (di/dt) of the high pulse power using the classic single HiPIMS pulse, or the high pulse package mode, will be presented by the measured OES system of the related thin film structures.

This study will present circuit applications and resulting of micro structure and

properties of the deposited coatings using an industrial PVD equipment. The coatings are deposited from a metallic Ti target in a reactive mode with Ar-N₂ and Ar-N₂-CH₄ as gas mixtures, respectively under different target power and gas pressure.