Target Power Density Research Articles

Modulated pulse power sputtered chromium coatings

Cr coatings were deposited using continuous dc magnetron sputtering (dcMS) and modulated pulse power sputtering (MPP) techniques in a closed field unbalanced magnetron sputtering system at equivalent average target powers. It was found that MPP sputtering exhibited higher deposition rates than in dcMS when the average target power density was above 14Wcm−2 for the Cr coating depositions. Plasma diagnostics confirmed a significant increase in the numbers of both target material (Cr) and gas (Ar) ions in the MPP plasma as compared to the dc plasma. The substrate peak current densities measured in the MPP depositions (104–324mAcm−2) have been increased by over a factor of 50 to those in the dcMS conditions (2–5.5mAcm−2). The enhanced ion flux bombardment from the highly ionized MPP plasma led to the formation of denser microstructure and finer grain size in the MPP Cr coatings than in the dcMS Cr coatings. In addition, MPP sputtered Cr coatings exhibited improved hardness and adhesion.

Carbon and Tungsten Sputtering in a Helium Magnetron Discharge

This paper reports on carbon and tungsten deposition on a heated silicon substrate under He <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> bombardment in a magnetron-sputtering device. The discharge was operated at constant pressure of 1.33 Pa for two discharge-current intensities (200 and 600 mA) and target power density up to 40 Wmiddotcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> . The deposited films were characterized by scanning electron microscopy, atomic force microscopy, and X-ray diffractometry. The topography and cross section revealed the influence of the target power density on the surface roughness, grains' size, and thickness of the deposited films.

Electron energy distributions and plasma parameters in high-power pulsed magnetron sputtering discharges

We report on the results obtained using time-resolved Langmuir probe measurements in high-power pulsed dc magnetron sputtering discharges. Time evolutions of the electron energy distribution and the local plasma parameters were investigated at a substrate position of 100 mm from a planar target of 100 mm diameter during a high-rate deposition of copper films. The average target power density in a pulse was 500 W cm−2 at a repetition frequency of 1 kHz, a voltage pulse duration of 200 µs and an argon pressure of 1 Pa. The electron energy distributions with two energy groups and sharply truncated high-energy tails were observed during a pulse. After a fast rise in a 50 µs initial stage of the pulse, the kinetic temperature of electrons, defined using the mean electron energy, remained in the range from 10 500 to 12 200 K till the pulse termination. The temperature of weakly populated hot electrons decreased rapidly in the initial stage of the pulse approaching the kinetic temperature approximately 100 µs after a pulse initiation. High plasma densities, being in the range 1 × 1012–2 × 1012 cm−3 for 100 µs, were achieved at the substrate position with a 50 µs delay after establishing the 125 µs steady-state discharge regime with the target power density of 650–680 W cm−2 during a pulse. The plasma potential slowly increased from 0.5 to 3.5 V during the pulse and 25 µs after its termination.

X線法によるポリイミド基板スパッタ銅薄膜の変形挙動の評価

Copper thin films were fabricated by RF-magnetron sputtering under target power densities of 0.5 and 5W/cm^2. The polyimide film was used as a substrate to apply a plastic deformation to the copper thin film. Average grain sizes of the copper films obtained at 5W/cm^2 were 125nm and 230nm. On the other hand, the sizes at 0.5W/cm^2 were about 50nm. Load-controlled and strain controlled cyclic deformation tests were conducted on the polyimide films where the copper films deposited. Stress, full width at half maximum (FWHM) of diffraction profile, crystallite size, and microstrain of the copper films were measured during the deformation tests using X-ray method. In the load-controlled tests, the crystallite size decreased with applied strain during loading period, although the applied strain hardly affect crystallite size during unloading. On the other hand, the microstrain during unloading period was sensitive to the applied strain: the microstrain increased after initial rapid decrease. In the strain-controlled tests, the X-ray stress averaged over a strain cycle decreased with strain cycles. This is because the copper film was subjected to large plastic deformation which can cause internal compressive stress during unloading. The averaged value of the FWHM decreased also with strain cycles. This decrease in the FWHM was consistent with texture development during cyclic loading. On the other hand, the changes in the crystallite size and the microstrain during cyclic loading were insignificant.

On the carbon and tungsten sputtering rate in a magnetron discharge

Magnetron discharge as sputtering source can serve as an alternative tool for the study of the plasma-wall interaction, with applications for ITER divertor. The present work reports on the influence of the target power density and the nature of the projectile on the erosion of C and W targets. The experimental results concern the sputtering rate of carbon and tungsten targets of a d.c. magnetron discharge in argon and helium atmosphere, at different gas pressures in the range of 10–100mTorr and discharge power densities up to 40Wcm−2 while the discharge current intensity was used as control parameter. In this investigation, carbon and tungsten sputtering rates were measured using two conventional methods based on gravimetric mass loss and profilometry. Target erosion profiles were compared with the profiles of the ion energy flux bombarding the target, calculated from a 2D fluid model.

Characteristics of sputtered amorphous carbon films prepared by a closed-field unbalanced magnetron sputtering method

We discuss the tribological performance of sputtered amorphous carbon (a-C) films deposited by closed-field unbalanced magnetron (CFUBM) sputtering with a graphite target using a mixture of helium (He) and argon (Ar) as sputtering gases. We investigated the effects of the graphite target power density on the micro-structural and physical properties. In the Raman spectra, the G-peak position moved to the higher wavenumbers. The ID/IG ratio increased with the increase of target power density in the fixed DC bias voltage. This was the result of the structural change in the a-C film that resulted with the increase in sp2 bonding fraction. Also, the maximum hardness of the a-C film was 23 GPa, the friction coefficient was 0.1, and the critical load was 25.9 N on the Si wafer. In addition, the compressive residual stress of the film increased a little with increasing target power density. Consequently, the various properties of a-C films, with an increase of the target power density, were associated with the increase of cross-linked sp2 bonding fraction and the cluster size. The tribological properties of a-C film showed clear dependence on the energy of ion bombardment with the increase of plasma density during film growth.

Pulsed dc self-sustained magnetron sputtering

The magnetron sputtering has become one of the commonly used techniques for industrial deposition of thin films and coatings due to its simplicity and reliability. At standard magnetron sputtering conditions (argon pressure of ∼0.5Pa) inert gas particles (necessary to sustain discharge) are often entrapped in the deposited films. Inert gas contamination can be eliminated during the self-sustained magnetron sputtering (SSS) process, where the presence of the inert gas is not a necessary requirement. Moreover the SSS process that is possible due to the high degree of ionization of the sputtered material also gives a unique condition during the transport of sputtered particles to the substrate. So far it has been shown that the self-sustained mode of magnetron operation can be obtained using dc powering (dc-SSS) only. The main disadvantage of the dc-SSS process is its instability related to random arc formation. In such case the discharge has to be temporarily extinguished to prevent damaging both the magnetron source and power supply. The authors postulate that pulsed powering could protect the SSS process against arcs, similarly to reactive pulsed magnetron deposition processes of insulating thin films. To put this concept into practice, (i) the high enough plasma density has to be achieved and (ii) the type of pulsed powering has to be chosen taking plasma dynamics into account. In this article results of pulsed dc self-sustained magnetron sputtering (pulsed dc-SSS) are presented. The planar magnetron equipped with a 50mm diameter and 6mm thick copper target was used during the experiments. The maximum target power was about 11kW, which corresponded to the target power density of ∼560W∕cm2. The magnetron operation was investigated as a function of pulse frequency (20–100kHz) and pulse duty factor (50%–90%). The discharge (argon) extinction pressure level was determined for these conditions. The plasma emission spectra (400–410nm range) and deposition rates were observed for both dc and pulsed dc self-sustained sputtering processes. The pulse characteristics of the voltage and current of the magnetron source during pulsed dc-SSS operation are shown. The presented results illustrate that a stable pulsed dc-SSS process can be obtained at a pulsing frequency in the range of 60–90kHz and duty factor of 80%–90%.

Highly ionized fluxes of sputtered titanium atoms in high-power pulsed magnetron discharges

High-power pulsed dc magnetron discharges for ionized sputtering of titanium films were investigated. The depositions were performed using a strongly unbalanced magnetron source with a planar titanium target of 100 mm diameter. The repetition frequencies were 1 and 20 kHz at 20% and 50% duty cycles and argon pressures of 0.5 and 5 Pa. Time evolutions of the discharge characteristics were measured at a target power density in a pulse up to 740 W cm−2. Time-averaged mass spectroscopy was carried out at substrate positions of 100 and 200 mm from the target. It was shown that argon ions are predominant (69–81%) in total ion fluxes onto the substrate. The Ti+ and Ar+ ion energy distributions with broadened low-energy peaks are extended to higher energies (50 eV relative to the ground potential). The ionized fraction of sputtered titanium atoms in the flux onto the substrate was in the range from 60% to 99%.

Medium frequency magnetron self-sputtering of copper

It is well known that the magnetron self-sustained sputtering (SSS) process can be achieved in the direct current (DC) operation mode (DC-SSS) if certain conditions are fulfilled: high self-sputtering yield of the target material (theoretically Y>1), appropriate magnetron source design, high target power density to ensure high ionization level of the sputtered material. The main disadvantage of the DC-SSS process is the instability related to possibility of an arc formation. The author postulates that magnetron plasma pulsing can minimize this problem. In this paper, voltage and current waveforms of medium frequency (MF) powered magnetron source are analysed. A simple electrical model, explaining dynamics of MF magnetron discharge is presented. The method to achieve MF magnetron SSS process is proposed and experimentally verified. The results of MF magnetron SSS (MF-SSS) process are presented for the first time (to the author's knowledge). The experiments were performed using a planar magnetron source equipped with a copper target of 50 mm in diameter and 6 mm thick. The magnetron source was powered by a resonant (110 kHz) power supply. The target power density during MF-SSS process was about 490 W/cm 2.

Characterization of DC magnetron sputtered diamond-like carbon (DLC) nano coating

Development in vapor deposition techniques over the last two decades has led to the introduction of many advanced coatings for metal-cutting tools. This paper examines the characteristics of multilayer Ti, TiN, and diamond-like carbon (DLC) coatings deposited on standard tool substrates at varying sputtering parameters and conditions, such as power density, partial pressure, substrate temperature, and reactive gases. The characteristics of films were examined using an X-ray diffractometer, Raman microscope, surface profilometer (to measure the thickness of the coating), Rockwell hardness tester (to test adhesion), and a micro hardness tester. The pin-on-disc test setup was used to find the coefficient of friction of the coatings. The results indicated that a graded multilayer coating showed better adhesion to the substrates. It was observed that higher target power density resulted in an increase of micro hardness and crystalline planes of coating. Lattice constant matching among layers of coating, proper substrate preparation, and a sequence of cleaning processes are the crucial factors for the enhancement of adhesion strength.

Optimization of Configuration for Cube-Shaped SOFC Bundles

Solid oxide fuel cells (SOFCs) have serious problems under heating cycle. As a solution for this problem, use of micro- tubular SOFCs is considered for robustness under rapid changes of operating temperature. We fabricated cube-shaped SOFC bundles with following method; Micro-tubular Gd-CeO2(GDC)-NiO anode was fabricated by extrusion, and then was co-fired with GDC electrolyte coated on the surface of the anode tube. La0.6Sr0.4Co0.2Fe0.8O3-x (LSCF) cathode matrices with grooves were also prepared by extruding of a mass with LSCF powder and pore-former. Then, the tubes were arranged in the grooves of LSCF cathode matrices, where the tubes and the matrices were jointed with LSCF pastes. Optimization of the micro tubular cell configuration in cube-shaped SOFC bundles and microstructure of cathode is important to achieve our target power density (2W/cm3). In this study, we considered the configuration of cube-shaped SOFC bundles and investigated the character of single tubular cell and cathode porous matrices.

High-rate low-temperature dc pulsed magnetron sputtering of photocatalytic TiO2films: the effect of repetition frequency

The article reports on low-temperature high-rate sputtering of hydrophilic transparent TiO2thin films using dc dual magnetron (DM) sputtering in Ar + O2mixture on unheated glass substrates. The DM was operated in a bipolar asymmetric mode and was equipped with Ti(99.5) targets of 50 mm in diameter. The substrate surface temperature Tsurfmeasured by a thermostrip was less than 180 °C for all experiments. The effect of the repetition frequency frwas investigated in detail. It was found that the increase of frfrom 100 to 350 kHz leads to (a) an improvement of the efficiency of the deposition process that results in a significant increase of the deposition rate aDof sputtered TiO2films and (b) a decrease of peak pulse voltage and sustaining of the magnetron discharge at higher target power densities. It was demonstrated that several hundreds nm thick hydrophilic TiO2films can be sputtered on unheated glass substrates at aD = 80 nm/min, Tsurf < 180 °C when high value of fr = 350 kHz was used. Properties of a thin hydrophilic TiO2film deposited on a polycarbonate substrate are given.

High-power pulsed sputtering using a magnetron with enhanced plasma confinement

High-power pulsed dc magnetron discharges for ionized high-rate sputtering of metallic films were systematically investigated. The depositions were performed using two unbalanced circular magnetrons of different types with a directly water-cooled planar copper target of 100mm in diameter. The repetition frequency was 1kHz at a fixed 20% duty cycle and an argon pressure of 0.5Pa. Time evolutions of the discharge characteristics were measured to provide information on absorption of energy in the discharge plasma and on transfer of arising ions to the substrate at a target power density in a pulse up to 950W∕cm2. Time-averaged mass spectroscopy was performed at the substrate position to characterize ion energy distributions and composition of total ion fluxes onto the substrate. The deposition rate of the copper films formed on a floating substrate at the distance of 100mm from the target was 2.2μm∕min at an average target power density over a pulse period of 96W∕cm2. Very effective ionization of sputtered copper atoms resulted in a strong predominance of copper ions (up to 92%) in total ion fluxes onto the substrate. Trends in measured values of the deposition rate per average target power density and the ionized fraction of sputtered copper atoms in the flux onto the substrate (up to 56%) were explained on the basis of model predictions.

Parametric study of sputtered Sr-deficient SrBi2Ta2O9 thin films

Sr-deficient SrBi2Ta2O9 (SBT) thin films for nonvolatile ferroelectric random access memory applications were deposited by radio-frequency magnetron sputtering on Pt∕Ta∕SiO2∕Si substrates. The effect of deposition parameters on microstructures and chemical composition were studied using x-ray diffraction (XRD), field emission scanning electron microscopy, and x-ray photoelectron spectroscopy (XPS). The composition of the films was dependent on the sputtering conditions. The undesirable pyrochlore phase could be eliminated by adjusting process pressure, target power density, and target-to-substrate distance. The evolution of microstructures at various deposition conditions was attributed to changes in the Bi∕Ta and Sr∕Ta ratios. When Sr became deficient and Bi excessive (Sr0.74Bi2.2Ta2O9+x as determined by XPS), no pyrochlore phase was detected with XRD. Under an electric field of 240kV∕cm, the Sr-deficient SBT film demonstrated a remnant polarization (2Pr) of 11.6μC∕cm2 and a coercive field (2Ec) of 96kV∕cm.

Effect of target power and composition on RE–Fe–B thin films with Cu and Nb buffer and cap layers

We report a systematic study of the structural, morphological, and magnetic properties of RE–Fe–B (RE=rareearth) films codeposited onto thermally oxidized Si substrates. The use of Cu and Nb buffer and cap layers was investigated. The deposition of the samples was performed by magnetron sputtering with the substrates held at 470°C and using various Fe target power densities and fixed RE:Fe:B target power density. This was done in order to vary the growth rate and the Fe content of the films. The simultaneous increase of the deposition rate and Fe content influenced the c-axis texturing of the samples. For the Cu∕RE:Fe:B∕Cu films, as a consequence of the good perpendicular intrinisic coercivity (∼492kA∕m at 10W) and very high remanent polarization (∼1.51T at 110W), very good perpendicular energy products were obtained at 10W (∼133kJ∕m3) and 110W (∼136kJ∕m3). The Nb∕RE:Fe:B∕Nb samples had the best combination of perpendicular energy product and intrinsic coercivity, with values of 150kJ∕m3 and 800kA∕m, respectively, for an iron target power of 20W. This high energy product was retained up to target powers of 50W in spite of the intrinsic coercivity decreasing rapidly with increasing power beyond 20W, because of a marked increase in remanent polarization.

Sputtering Deposition Parameters and Their Interactions in Amorphous Tungsten Oxide Thin Film as Electrochromic Electrode

Amorphous tungsten oxide (a-WO3) thin films were deposited as electrochromic electrodes on ITO coated glass substrates via reactive DC magnetron sputtering from metallic tungsten target. A two-level full-factorial design-of-experiment (DoE) was carried out with the following variables: 1) sputter target power density, 2) total pressure, 3) oxygen to argon flow ratio and 4) deposition time. Characterizations via lithium intercalation in potentiostatic mode were conducted in a wet electrochemical cell. Our work shows that parameters interaction should be considered in optimizing WO3 thin film for electrochromic applications. Work based on a factorial design reduces the number of experiments and allows reaching near-optimized region with small amount of effort.

A study of hard diamond-like carbon films in mid-frequency dual-magnetron sputtering

A series of hydrogen-free diamond-like carbon (DLC) films were deposited by a mid-frequency dual-magnetron sputtering under basic conditions of Cr and C target power density between 6 and 18 W/cm 2, bias voltage in a range of − 100 V to − 200 V, and a pure argon atmosphere. Microstructure, microhardness, adhesion, friction and wear properties were investigated for the DLC films to be used as protective films on cutting tools and forming dies, etc. The DLC films exhibited some combined superior properties: high hardness of 30–46 GPa, good adhesion of critical load of 50–65 N, and friction coefficient about 0.1 in air condition. Properties of the magnetron-sputtered carbon films showed a strong dependence on flux and energy of ion bombardment during growth of the films.

Effect of the target power density on the synthesis and physical properties of sputtered nc-C films

Hydrogen-free nanostructured carbon (nc-C) films were synthesized at various graphite target power densities using a closed field unbalanced magnetron sputtering system (CFUBM). The power density of each graphite target was varied from 10 to 30 W/cm 2 in Ar gas atmosphere with a fixed pressure of 0.4 Pa and a substrate bias voltage of−200 V. The aim of this study was to determine the relationship between the microstructure and physical properties of nc-C films as a function of the target power density. The film structures were examined by Raman spectroscopy, X-ray photoelectron spectroscopy and field emission scanning electron microscopy. The physical properties of the nc-C films were evaluated using a nano-indentation tester, a 4-point probe and a residual stress tester. The number of graphitic nano-cluster increased with increasing target power density and a good conductive nanostructured carbon film was obtained. The nc-C film deposited at a target power density of 30 W/cm 2 exhibited the minimum electrical resistivity.

High-rate deposition of copper thin films using newly designed high-power magnetron sputtering source

We have deposited copper (Cu) thin films on Si(100) and glass substrates in the growth temperature range between 573 and 753 K using a pulsed DC magnetron sputtering method. Based on the magnetic field simulation, we have designed and constructed a high-power (120×10 −4 W/m 2) unbalanced magnetron sputtering (UBM) source for high-rate deposition. The maximum deposition rate of the newly developed sputtering source under a target power density of 115×10 −4 W/m 2 we have obtained is 2.8 μm/min. This is five times higher than that using the conventional sputtering method, and the sputtering yield also reached 70% due to low voltage and high-current Cu-accelerated ions. We have also adapted an ion extraction grid between the Cu target and substrate. Although the growth rate was decreased to 2 μm/min, XRD and XPS showed that highly oriented polycrystalline Cu(111) thin films without carbon and oxygen impurities were obtained with lowest electrical resistivity of 2.0×10 −2 μΩm at a target power density of 96.7×10 −4 W/m 2, substrate temperature of 723 K, and working pressure of 1.3×10 −1 Pa. During film deposition, moreover, plasma diagnostics was also carried out in situ by optical emission spectroscopy analysis.

Effect of sputtering target power density on topography and residual stress during growth of nanocomposite nc-TiN/a-SiN x thin films

Nanocrystalline TiN (nc-TiN) has been imbedded in amorphous silicon nitride (a-SiN x ) matrix to form a nanocomposite thin film (nc-TiN/a-SiN x ) via magnetron sputtering. Adjusting Ti and Si 3N 4 target power ratio alters film composition, morphology, microstructure and residual stresses. The effects of silicon nitride target power density on surface morphology and residual stress have been studied. Atomic force microscopy (AFM) shows that the film surface becomes increasingly smoother and the roughness ( R a) drops from about 6 nm down to less than 1 nm as the silicon nitride target power density increases from 1.1 to 5.5 W cm −2. The surface topography is quantitatively described by calculation of two parameters: the interface width ( w) and the lateral correlation length ( ξ). The interface width ( w) describes the vertical growth, and the lateral correlation length ( ξ) characterizes the lateral growth of the surface. The growth-induced residual stress during the sputtering deposition of nc-TiN/a-SiN x nanocomposite thin film increases with sputtering power density, but only reaches about −1 GPa even at the highest experimented Si 3N 4 target power density of 5.5 W cm −2. The growth-induced stress is opposite in sign and roughly equal in quantity to the thermal stress induced by the difference in the coefficient of thermal expansion (CTE) between the films and the silicon wafer substrate. As a result, the magnetron sputtered nc-TiN/a-SiN x nanocomposite films become almost stress-free (as low as 0 to −0.15 GPa residual stress).