High Power Impulse Magnetron Sputtering Process Research Articles

The Enhanced Performance of Oxide Thin-Film Transistors Fabricated by a Two-Step Deposition Pressure Process.

It is usually difficult to realize high mobility together with a low threshold voltage and good stability for amorphous oxide thin-film transistors (TFTs). In addition, a low fabrication temperature is preferred in terms of enhancing compatibility with the back end of line of the device. In this study, α-IGZO TFTs were prepared by high-power impulse magnetron sputtering (HiPIMS) at room temperature. The channel was prepared under a two-step deposition pressure process to modulate its electrical properties. X-ray photoelectron spectra revealed that the front-channel has a lower Ga content and a higher oxygen vacancy concentration than the back-channel. This process has the advantage of balancing high mobility and a low threshold voltage of the TFT when compared with a conventional homogeneous channel. It also has a simpler fabrication process than that of a dual active layer comprising heterogeneous materials. The HiPIMS process has the advantage of being a low temperature process for oxide TFTs.

Dielectric properties of hafnium oxide film prepared by HiPIMS at different O2/Ar ratios and their influences on TFT performance

High-k hafnium oxide (HfO2) film was prepared by high power impulse magnetron sputtering (HiPIMS). The influences of oxygen supply on the plasma state, film properties and TFT performance were investigated. The films are near-stoichiometric and preferentially (−1 1 1)-orientated. When the oxygen supply increased from 1% to 3%, the excitation/ionization rate of the plasma species increased, leading to higher crystallinity, higher density, and lower oxygen vacancy defect concentration of the film, therefore improving the dielectric properties of the film. When the oxygen supply further increased to 5%, the excitation/ionization rate decreased, thereby leading to lower crystallinity, lower density, and higher oxygen vacancy defect concentration of the film, therefore deteriorating the dielectric properties of the film. The film deposited at 3% oxygen supply exhibited the best dielectric properties with the highest k value of 24 and the highest breakdown-electric field (4.7 MV/cm), which should be attributed to the high crystallinity, high density and low oxygen vacancy defect concentration of the film. Finally, transparent thin film transistors (TFTs) with ITO gate electrode, HfO2 gate dielectric layer and indium-gallium-zinc oxide channel were fabricated on flexible colorless polyimide substrate at full room temperature by all HiPIMS process. The fixed positive charges and k value of HfO2 film have significant effects on the TFT performance. The best TFT exhibited good electrical performance, featuring a remarkably low subthreshold swing of 0.13 V/decade. It also exhibited fair stability against bending and gate bias stress.

A comparative study on the hardness, stress and surface free energy of HfN films grown by HIPIMS and direct-current magnetron sputtering

HfN films with rocksalt structure have been grown by high-power impulse magnetron sputtering (HIPIMS) with various duty cycles, in a comparison with direct-current magnetron sputtering (dcMS) process. Such two sputtering processes yield the quite close compositions. Increasing the duty cycle from 7.5 % to 9 % and 11 % in HIPIMS process, a compressive stress rises up from 1.5 to 1.9 and 2.1 GPa, which is much smaller than the value of 3.8 GPa from dcMS. The hardness of such low-stressed HfN films has been identified to be 25.5–25.9 GPa, which agrees well with the theoretical one of 22.5 GPa by the density functional theory without the consideration of stress. In addition, the surface free energy of 26.3–29.0 mJ/m2 has been determined in HfN films grown by HIPIMS, much lower than that of 31.5 mJ/m2 of the films grown by dcMS.

Ti-Al-C Based MAX Phase Coating As Corrosion Protection for Ferritic Bipolar Plates

Metallic bipolar plates in fuel cells have the advantages of high electrical conductivity, low permeability to the reactants and gases, and easy manufacturability. However, resistance to corrosion under long term operation conditions limits their practical use in the fuel cell. Owing to the importance of corrosion stability, materials such as austenitic stainless steels, Ni-based alloys and coated titanium or stainless steel plates are currently being used in bipolar plates, although ferritic steels would be cost effective. A pinhole-free anticorrosion coating can help in application of the ferritic steels in fuel cells. MAX phase materials offer excellent corrosion stability and high electronic conductivity and have been successfully tested for corrosion protection of metallic bipolar plates. In the current work, Ti-Al-C-based MAX phase coatings were prepared using high power impulse magnetron sputtering (HiPIMS). The HiPIMS process was in some cases also combined with plasma immersion ion implantation (PIII) to study the influence of the high energetic ion implantation process on the structure and performance of the resulting MAX phase layer. The deposited samples were annealed at 800 °C for 2 h in Ar atmosphere. The structure and composition of the coatings produced were studied with X-ray photoelectron spectroscopy, atom probe tomography and transmission electron microscopy. The corrosion performance of the layers was studied using a scanning flow cell coupled with inductively coupled plasma mass spectroscopy.

Influence of Voltage, Pulselength and Presence of a Reverse Polarized Pulse on an Argon–Gold Plasma during a High-Power Impulse Magnetron Sputtering Process

This work aims to provide information about the deposition of gold via bipolar high-power impulse magnetron sputtering (HIPIMS) in order to identify suitable process parameters. The influences of voltage, pulse length and the kick-pulse on an argon–gold plasma during a bipolar high-power impulse magnetron sputtering deposition process were analysed via optical emission spectroscopy (OES) and oscilloscope. The voltage was varied between 700 V and 1000 V, the pulse length was varied between 20 µs and 100 µs and the process was observed once with kick-pulse and once without. The influence of the voltage on the plasma was more pronounced than the influence of the pulse width. While the intensity of several Au I lines increased up to 13-fold with increasing voltages, only a less-than linear increase in Au I brightness with time could be identified for changes in pulse length. The intensity of excited argon is only minimally affected by changes in voltages, but follows the evolution of the discharge current, with increasing pulse lengths. Contrary to the excited argon, the intensity emitted by ionized argon grows nearly linearly with voltage and pulse length. The reverse polarised pulse mainly affects the excited argon atoms in the plasma, while the influence on the ionized argon is less pronounced, as can be seen in the the spectra. Unlike the excited argon atoms, the excited gold atoms appear to be completely unaffected by the kick-pulse. No ionization of gold was observed. During the pulse, a strong rarefaction of plasma takes place. Very short pulses of less than 50 µs and high voltages of about 1000 V are to be preferred for the deposition of gold layers. This paper offers a comprehensive overview of the gold spectrum during a HIPIMS process and makes use of optical emission spectroscopy as a simple measuring approach for evaluation of the reverse polarized pulse during a bipolar process. Future uses of the process may include the metallization of polymers.

Low-density HiPIMS favored ultrathick and compact chromium coatings on Zircaloy-4 alloys

Protective metallic coatings are receiving increasing attention to modify the anti-corrosion and oxidation resistance of zirconium-based fuel cladding tubes under harsh high-temperature steam/air oxidation conditions. In this work, ultrathick (∼20 μm) and compact Cr coatings with (001) preferential orientation were deposited on Zircaloy-4 (Zry-4) alloy by high power impulse magnetron sputtering (HiPIMS) technique. The growth characteristics of the Cr coatings were investigated as a function of the discharge plasma species, including Cr+, Cr*, Ar+, and Ar*, which were controlled by the different discharge modes during HiPIMS process. The results showed that, when the discharge feature was changed from the ‘low voltage direct current magnetron sputtering (DCMS)-like’ mode into a ‘low density HiPIMS’ mode, a rapid increase of Cr+ content in the substrate vicinity was obtained by time-integral optical emission spectra (OES), indicating a remarkably enhanced incident energy flux to the deposited Cr coating. The generalized temperature increment of the Cr coating growing surface calculated from the OES, was ∼100 K and was mainly affected by the incidence of Cr* atoms. A simplified collision model based on the non-penetrating ions/atoms assumption was also proposed to calculate the transferred energy from the incident energetic species and thus understand the predominant effect of HiPIMS Cr plasma on the achieved nanocrystalline Cr coating with ultra-thick and dense structure, which is still quite challenging for the DCMS deposition process.

Evidence of 1000 eV positive oxygen ion flux generated in reactive HiPIMS plasma

The arrival of highly energetic (near 1000 eV) positive atomic oxygen ions at the substrate region has been detected in a unipolar reactive high-power impulse magnetron sputtering process operated with an uncooled copper target in argon–oxygen mixtures. Examination of the ion fluxes from discharge plasma was performed with a magnetic sector mass-spectrometer and an electrostatic energy analyzer. The energy of fast positive O+ ions is close to the value of eV d (e—elementary charge, V d—discharge voltage), which indicates their connection to the well-studied fraction of negative O− ions, which undergo acceleration in the cathode sheath. After switching the oxygen gas supply off, the flux of energetic O+ species decreases gradually as the poisoned target surface layers become depleted of oxygen due to sputtering in pure argon. Presumably, the observed energetic O+ ions originate as a result of low-angle scattering of fast negative O− ions from other charged or neutral species in the plasma followed by electron detachment, ionization, or charge exchange.

Influence of substrate bias voltage on microstructure and mechanical characteristics of TiAlSiN coating deposited by High Power Impulse Magnetron Sputtering (HiPIMS)

Substrate bias voltage has a presumably predominant and significant influence on the microstructural morphology and mechanical properties of HiPIMS deposited coatings. In the present investigation, it has been investigated in depth for a quaternary coating, TiAlSiN coating, which was deposited on the cemented carbide (WC-10 wt% Co) substrates. In this HiPIMS process, a pair of TiAl60 and a pair of TiSi34 targets were used. Four different substrate biases were set, i.e., −60, −90, −120, and −150 V to explore the difference in the coating characteristics. In every case, the substrate bias was also applied in pulsed mode but with an offset of 40 μs to the cathode pulse. Both cathode current and bias current were observed to increase from 87 to 98 A and 19 to 23 A, respectively, with increase of substrate bias voltage. As the bias voltage increased, the surface morphology became finer, and the cross-section morphology turned to be highly denser. The minimum and maximum grain sizes were estimated to be 7.23 nm and 9.90 nm at a substrate bias of −60 V and −150 V, respectively. Variation of Ti content (at.%) was noticed in the range of 28.35 to 30.71 with the increase of bias voltage. The maximum hardness of the coating was recorded to be 42.95 GPa at the bias voltage of −150 V. The adhesion level has been classified under HF1 in all deposition cases, as investigated by Rockwell indentation method, whereas the scratch test results suggest that a load range between 154 and 161 N is required for the complete delamination of the coating. Spallation and edge-chipping were the primary failure mechanisms during the scratching of the TiAlSiN coating.

Transparent Silver Coatings with Copper Addition for Improved Conductivity by Combined DCMS and HiPIMS Process

The demand for transparent conductive coatings has increased over recent years, leading to the development of various technical solutions. One of the approaches is to use metallic coatings very close to their coalescence thickness, so that a good compromise between transparency and conductivity is obtained. In this contribution, a combination of two elements with high potential in this field is used, namely silver and copper. The continuity of silver films on a dielectric transparent substrate is significantly improved by the addition of a copper seed layer that promotes the formation of a continuous layer at smaller effective thicknesses. Two distinct deposition processes are used for the deposition of the two materials, namely HiPIMS (High Power Impulse magnetron sputtering) for copper and DC sputtering for silver. The use of HiPIMS enables a better control of the structure and quantity of deposited material, allowing us to deposit a very small amount of material. The mono-element coatings are characterized from the optical and electrical point of view, and then mixed to form a structure with better transparency, up to 80% in the visible spectrum, good electrical properties, resistivity of ~2 × 10−5 (Ω × cm), and significantly lower surface roughness, down to 0.2 nm.

Modelling of dcMS and HiPIMS process with hydrocarbon gas admixture

Magnetron sputtering in an argon and hydrocarbon gas mixture is a complex deposition process exhibiting features of both physical vapour deposition and plasma enhanced chemical vapour deposition. The hydrocarbon gas decomposes within the plasma and then it is able to form a carbide phase with the target metal atoms or to be deposited as amorphous carbon. In this paper, a simple model for both the direct current (dcMS) and the high power impulse magnetron sputtering (HiPIMS) processes with hydrocarbon gas admixture is presented. The sputtered target racetrack is divided into metallic, compound, and carbon fractions to take into account both the carbide formation and the carbon deposition. To simulate the HiPIMS process, the back-attraction of ionised sputtered metal particles is incorporated into the model. The model is cross-validated with the previously published experiments which were conducted using the same deposition apparatus allowing for the direct comparison of the dcMS and HiPIMS processes. The simulated results correlate with the measured dependencies of the deposition rate, the carbon content in deposited films, and the racetrack fractions on the acetylene supply rate. The presented model is further successfully validated with the evolution of the racetrack composition calculated by SDTrimSP.

Temporal studies of titanium ionised density fraction in reactive HiPIMS with nitrogen admixture

Temporal evolutions of the ground state number densities of titanium atoms and ions and the ionised density fraction during pulse on-time are experimentally investigated for the high-power impulse magnetron sputtering process in an Ar and Ar/N2 atmosphere. For the study, two distinct pulses with the same pulse length at a constant average power but different pulse off-times were selected. In both conditions, four representative points within the hysteresis curve were chosen, and the time evolutions of sputtered species densities were investigated in both the target and the substrate regions. At the pulse beginning, a high density of residual particles sputtered during the previous pulse is present in both studied regions. In the target region, in conditions of longer pulse off-time and thus higher peak discharge current, 95% of sputtered particles are ionised in metallic, transition and compound regimes. With shorter pulse off-time conditions, and thus a lower peak discharge current, the ionised density fraction is the lowest in the metallic regime; in the transition and compound regimes, it exceeds 80%. In the substrate region, the temporal evolution of sputtered species densities differs from that obtained in the target region. After the pulse ignition, titanium atoms and ions remaining near the substrate from the previous pulse are pushed away. In the metallic regime, the sputtered atoms refill the substrate region already during the pulse on-time in both the low- and high-current conditions. In the high-current conditions, the titanium ions arrive at the substrate together with the sputtered atoms; however, in the low-current conditions, the titanium ion density decreases during the pulse on-time, and the titanium ions arrive later during the pulse off-time. In the transition and compound regimes, both densities steadily decrease during the pulse on-time and the titanium atoms and ions arrive at the substrate during the pulse off-time.

Influence of a short reverse positive HPPMS pulse on the deposition of CrAlN

In conventional high power impulse magnetron sputtering processes (HPPMS) short pulses of a negative voltage are used to maintain the discharge. A new approach to accelerate ionized species towards the substrate position and subsequently improved coating properties is the use of a power supply, which generates a reverse positive pulse immediately after the negative pulse. In the present paper the influence of the frequency f and the pulse on time t on for a CrAlN process on the coating properties is investigated. All experiments were carried out on an industrial scale coating unit. In the present investigations coatings deposited by three different duty cycles are compared. For each duty cycle one coating was deposited using a conventional power supply and one coating using a power supply with a positive pulse. The positive pulse was clearly detected. It was found that the height of the positive pulse depends on the chosen pulse parameters. Furthermore, higher values of the peak power were found when using a power supply with a positive pulse, which should influence the ionization of the sputtered material. Regarding the chemical composition, a decreasing nitrogen content of the coatings was found when using a positive pulse. The investigations of the deposited coatings showed a denser morphology and increased values of the indentation hardness when using a power supply with a positive pulse compared to a conventional power supply. In addition to the higher indentation hardness, even the amount of plastic work showed increasing values for the power supply using a positive pulse compared to the conventional power supply. Furthermore, increased values of the roughness for coatings deposited on cemented carbide were found when using a positive pulse. The coatings deposited on cemented carbide showed a higher adhesion when using a positive pulse. • Higher peak power when using a short reverse positive pulse • Improved mechanical properties when using a positive pulse • Preferred (200) orientation for the use of a short reversed positive pulse and low duty cycles • Improved adhesion when using a positive pulse

ITO-free silver-doped DMD structures: HiPIMS transparent-conductive nano-composite coatings for electrochromic applications

Nanocomposites of dielectric/metal/dielectric (DMD) materials that are both optically transparent and electrically conductive are of great interest for an array of modern optoelectronic applications, including electrochromic and energy storage devices. Here we report for the first time the creation of ITO-free DMD nanocomposite structures that are composed of only three layers: (Ag-doped WO3)/(Ag)/(WO3). We employed high power impulse magnetron sputtering (HiPIMS) as a new technology to deposit the internal WO3 layer and the external Ag/WO3 nanocomposite. High rates of silver ionization in the HiPIMS process and energetic arrival of silver ions on the negatively biased DMD structure enabled their penetration into the external tungsten oxide layer, forming a nanocomposite structure in a single-step process. We provided evidence that this unique structure pushes the performance of transparent-conductive DMD materials beyond their intrinsic limits. To optimize the surface plasmon resonance effect and thus the electrochromic performance of the structures, we changed the size of silver nanoclusters through vacuum post-annealing in the same sputtering chamber at varied temperatures. The optimized Ag-WO3/Ag/WO3 structure was transparent (average transmittance = 75.89 ± 0.05% in the wavelength range of 300–700 nm) and electrically conductive (sheet resistance = 23.6 ± 0.8 Ω/□). Moreover, it showed favorable electrochromic characteristics with high coloration efficiency (32.1 cm2 C−1), fast switching speed, and excellent long-term stability for at least 2000 cycles. The mechanisms of improvement in the electrochromic performance of such bifunctional structures underpinned by surface plasmon resonance, as modulated by the size and average distance of silver nanoclusters, are elucidated. The versatile new approach using HiPIMS for the fabrication of transparent-conductive nanocomposite coatings on ITO-free substrates holds great potential to manufacture next-generation optoelectronic materials such as electrochromic devices.

Effects of Input Power Ratio of AlCr/Ti Target on the Microstructural and Mechanical Properties of AlTiCrN Coatings Synthesized by a High-Power Impulse Magnetron Sputtering Process

In this study, five AlTiCrN nitride coatings were deposited via high-power impulse magnetron sputtering (HiPIMS). The AlTiCrN coatings were synthesized with high contents of Al or Ti and a lower fraction of Cr, using Ti and Al70Cr30 targets with five different input power ratios. Electron probe microanalyzer results revealed that the increased rate of Ti contents in the coatings can be divided into two regions due to the difference of power densities for HiPIMS (>0.5 kW/cm2) and modulated pulsed power (MPP) (<0.5 kW/cm2). The deposition rate and thickness of the coatings depended on the sputtering yield of two metal targets under HiPIMS and MPP modes. The grain size of the coatings decreased from 60 to 40 nm as the input power ratios of the AlCr/Ti targets decreased due to their lower thickness values and lower Al content. Selected area electron diffraction patterns and X-ray diffraction results revealed that the TiN and AlTiN phases can be found in the coating containing higher Ti content, whereas the AlN, CrN, and AlCrN phases were observed in the coating with a higher Al concentration. Nevertheless, decreasing the concentration of Ti had a detrimental effect on the mechanical properties of AlTiCrN coatings, due to a promotion in grain size and the formation of AlN, which is softer than TiN. It is noticed that our results differed from those in previous reports, in which a grain refinement effect was observed due to increasing Al content. In this work, the effect of processing the parameters of the HiPIMS and MPP power systems on the grain size and the mechanical property of the coating was also discussed.

Deposition of 3YSZ-TiC PVD Coatings with High-Power Impulse Magnetron Sputtering (HiPIMS)

Optimized coating adhesion and strength are the advantages of high-power impulse magnetron sputtering (HiPIMS) as an innovative physical vapor deposition (PVD) process. When depositing electrically non-conductive oxide ceramics as coatings with HiPIMS without dual magnetron sputtering (DMS) or mid-frequency (MF) sputtering, the growing coating leads to increasing electrical insulation of the anode. As a consequence, short circuits occur, and the process breaks down. This phenomenon is also known as the disappearing anode effect. In this study, a new approach involving adding electrically conductive carbide ceramics was tried to prevent the electrical insulation of the anode and thereby guarantee process stability. Yttria-stabilized zirconia (3YSZ) with 30 vol.% titanium carbide (TiC) targets are used in a non-reactive HiPIMS process. The main focus of this study is a parameter inquisition. Different HiPIMS parameters and their impact on the measured current at the substrate table are analyzed. This study shows the successful use of electrically conductive carbide ceramics in a non-conductive oxide as the target material. In addition, we discuss the observed high table currents with a low inert gas mix, where the process was not expected to be stable.

High Power Impulse Magnetron Sputtering of In2O3/Sn Cold Sprayed Composite Target

High Power Impulse Magnetron Sputtering (HiPIMS) was used for deposition of indium tin oxide (ITO) transparent thin films at low substrate temperature. A hybrid-type composite target was self-prepared by low-pressure cold spraying process. Prior to spraying In2O3 and oxidized Sn powders were mixed in a volume ratio of 3:1. Composite In2O3/Sn coating had a mean thickness of 900 µm. HiPIMS process was performed in various mixtures of Ar:O2: (i) 100:0 vol.%, (ii) 90:10 vol.%, (iii) 75:25 vol.%, (iv) 50:50 vol.%, and (v) 0:100 vol.%. Oxygen rich atmosphere was necessary to oxidize tin atoms. Self-design, simple high voltage power switch capable of charging the 20 µF capacitor bank from external high voltage power supply worked as a power supply for an unbalanced magnetron source. ITO thin films with thickness in the range of 30–40 nm were obtained after 300 deposition pulses of 900 V and deposition time of 900 s. The highest transmission of 88% at λ = 550 nm provided 0:100 vol. % Ar:O2 mixture, together with the lowest resistivity of 0.03 Ω·cm.

Improvement in the Figure of Merit of ITO-Metal-ITO Sandwiched Films on Poly Substrate by High-Power Impulse Magnetron Sputtering

High-power impulse magnetron sputtering (HiPIMS) was used to deposit ITO/Ag/ITO (IAgI) and ITO/Cu/ITO (ICuI) sandwiched films on polyethylene naphthalate substrate at room temperature as flexible transparent conductive materials. The hybrid layers were constructed with 40 nm ITO bottom and top layers, and a 5–20 nm Ag or Cu interlayer. The microstructure and optoelectrical properties were estimated for these films with various thicknesses of the metal interlayer. Thanks to the high-power density and highly ionized plasma in the HiPIMS process, the IAgI and ICuI sandwich structures exhibited good crystallinity and smooth surfaces with high optical transmittance and low sheet resistance. The optimal figure of merit was obtained as 101.16 × 10−3·Ω−1 for the IAgI film and 4.83 × 10−3·Ω−1 for the ICuI film with the metal interlayer thickness of 10 nm, both of which are higher than that from a similar structure reported via sputtering at room temperature. These results indicate that HiPIMS is a promising technique to deposit transparent conductive films onto soft substrates for applications in flexible optoelectronic devices.

Correlation between Substrate Ion Fluxes and the Properties of Diamond-Like Carbon Films Deposited by Deep Oscillation Magnetron Sputtering in Ar and Ar + Ne Plasmas

Recently, the use of Ne as a processing gas has been shown to increase the ionization degree of carbon in High Power Impulse Magnetron Sputtering (HiPIMS) plasmas. In this work, time-resolved measurements of the substrate’s current density were carried out in order to study the time evolution of the ionic species arriving at the growing film. The addition of Ne to the plasma resulted in a steep increase of the sp3/sp2 ratio in the films once the Ne contents in the processing atmosphere exceeded 26%. Increasing the Ne content is shown to increase both the total number of C ions generated in the plasmas and the ratio of C/gaseous ions. The time-resolved substrate ion current density was used to evaluate the possibility of substrate biasing synchronizing with the discharge pulses in the HiPIMS process. It is shown that in pure Ar plasmas, substrate biasing should be confined to the time interval between 25 and 40 µs after the pulse starts, in order to maximize the C+/Ar+ ratio bombarding the substrate and minimize the formation of film stresses. However, Ne addition to the processing gas shortens the traveling time of the carbon species towards the substrate, reducing the separation between the gaseous and carbon ion arrival times.

Complementary Metal-Oxide-Semiconductor Compatible Deposition of Nanoscale Transition-Metal Nitride Thin Films for Plasmonic Applications.

Transition-metal nitrides have received significant interest for use within plasmonic and optoelectronic devices because of their tunability and environmental stability. However, the deposition temperature remains a significant barrier to widespread adoption through the integration of transition-metal nitrides as plasmonic materials within complementary metal-oxide-semiconductor (CMOS) fabrication processes. Binary, ternary, and layered plasmonic transition-metal nitride thin films based on titanium and niobium nitride are deposited using high-power impulse magnetron sputtering (HIPIMS) technology. The increased plasma densities achieved in the HIPIMS process allow thin films with high plasmonic quality to be deposited at CMOS-compatible temperatures of less than 300 °C. Thin films are deposited on a range of industrially relevant substrates and display-tunable plasma frequencies in the ultraviolet to visible spectral ranges. Strain-mediated tunability is discovered in layered films compared to that in ternary films. The thin film quality, combined with the scalability of the deposition process, indicates that HIPIMS deposition of nitride films is an industrially viable technique and can pave the way toward the fabrication of next-generation plasmonic and optoelectronic devices.

Effect of substrate bias on microstructure of epitaxial film grown by HiPIMS: An atomistic simulation

The authors explore the combination of high power impulse magnetron sputtering (HiPIMS) and substrate bias for the epitaxial growth of the Cu film on the Cu (111) substrate by molecular dynamics simulation. A fully ionized deposition flux was used to represent the high ionization fraction in the HiPIMS process. To mimic different substrate bias, the authors assumed the deposition flux with a flat energy distribution in the low, moderate, and high energy ranges. The authors also compared the results of the fully ionized flux with results assuming a completely neutral flux, in analogy with thermal evaporation. It is confirmed that in the low energy regime, HiPIMS presents a slightly smoother surface and more interface mixing compared to that of thermal evaporation. In the moderate energy HiPIMS, however, an atomically smooth surface was obtained with a slight increase in the interface mixing compared to low energy HiPIMS. In the high energy regime, HiPIMS presents severe interface mixing with a smooth surface but limited growth due to resputtering from the surface. The results also indicate that fewer crystal defects appear in the film for moderate energy HiPIMS. The authors attribute this behavior to the repetition frequency of collision events. In particular, the high energy HiPIMS suffers from high repetition of collision events that does not allow the reconstruction of the film. While in the low energy HiPIMS, there are not enough events to overcome the island growth. At moderate energy, collision events repeat in a manner that provides enough time for reconstruction, which results in a smooth surface, fewer defects, and limited intermixing.