Magnetron Cathode Research Articles

Characterization of energetic and thermalized sputtered tungsten atoms using tuneable diode-laser induced fluorescence in direct current magnetron discharge

In this study a tuneable diode-laser induced fluorescence (TD-LIF) technique (λ0 = 407.4358 nm) is used to determine the atoms' velocity distribution function (AVDF) of energetic and thermalized sputtered tungsten (W) atoms in direct current magnetron discharge. The AVDF is characterized by probing the plasma above the centre of the target racetrack along the magnetron cathode axis in an argon–helium (Ar–He) mixture. Quantitative absorption measurements corroborated by deposition on silicon substrates are used to calibrate the TD-LIF relative measurements. Density, flux, temperature, AVDF and the flux velocity distribution function are derived from fitting the TD-LIF signals with four Gaussians (thermalized atoms) and four (energetic atom) functions (Stepanova and Dew 2004 Nucl. Instrum. Methods Phys. Res. B 215 357) taking into account the natural abundance and resonance wavelength shifts of the four main isotopes. Measurements show transport improvement for W atoms and an increase of the ratio of Ar ions to Ar neutrals with the increase of the percentage of He. All measurements are performed at 0.4 Pa and 100 W. The mean velocity of energetic W atoms typically ranges from 1900 to 2200 m s−1. The densities of thermalized and energetic atoms are in the same order of magnitude (∼109 cm−3) and their corresponding fluxes are several tens of times higher for energetic atoms (∼1015 cm−2 s−1).

Analytical model and measurements of the target erosion depth profile of balanced and unbalanced planar magnetron cathodes

The erosion depth profile of planar targets in balanced and unbalanced magnetron cathodes with cylindrical symmetry is measured along the target radius. The magnetic fields have rotational symmetry. The horizontal and vertical components of the magnetic field B are measured at points above the cathode target with z = 2 × 10−3 m. The experimental data reveal that the target erosion depth profile is a function of the angle θ made by B with a horizontal line defined by z = 2 × 10−3 m. To explain this dependence a simplified model of the discharge is developed. In the scope of the model, the pathway lengths of the secondary electrons in the pre-sheath region are calculated by analytical integration of the Lorentz differential equations. Weighting these lengths by using the distribution law of the mean free path of the secondary electrons, we estimate the densities of the ionizing events over the cathode and the relative flux of the sputtered atoms. The expression so deduced correlates for the first time the erosion depth profile of the target with the angle θ. The model shows reasonably good fittings to the experimental target erosion depth profiles confirming that ionization occurs mainly in the pre-sheath zone.

A modular bipolar power supply for high-power ion-plasma installations

The circuitry solutions, design, and main parameters of a modular pulse bipolar power-supply unit for high-power ion-plasma facilities are described. The modular principle of designing power supplies provided their application in various processes. The results of tests of the developed device as the power supply of a magnetron sputtering system with a power of 60 kW and a high-voltage power supply of the substrate bias voltage with a power of up to 40 kW are presented. The efficiency of applying bipolar pulses for preventing arcing at the magnetron cathode is experimentally demonstrated.

Ionization fraction of the sputtered metal flux in a hollow cathode magnetron

Results from studies of the parameters of a novel type of plasma source—a hollow cathode magnetron—are presented. The magnetron operates at a gas pressure of 5–20 mTorr, the discharge power being in the range of 0.5–4 kW. At discharge powers exceeding 2 kW, a plasma flow with a density of higher than 1011 cm−3 and length of up to 30 cm forms at the magnetron output. Using a grid quartz crystal microbalance, the ionized copper flux fraction was measured as a function of the gas pressure, discharge power, and distance from the target. At gas pressures of higher than 15 mTorr, the degree of ionization at a distance of 31 cm exceeds 50%.

Ionized sputtering with a pulsed hollow cathode magnetron

A hollow cathode magnetron has been operated with a HiPIMS power supply at duty cycles around 1%, and the non-reactive sputtering of several target materials such as copper, aluminum and carbon has been investigated. Systematically varying pulse length, frequency, discharge voltage, pressure and geometry of the magnetic field, waveforms of discharge voltage and current have been recorded. Beyond a material-specific voltage level, the pulse current always shows a runaway behavior stopped only at current densities above 10A/cm2 due to the limits of the power supply. Furthermore, the plasma has been characterized by time-averaged and time-resolved optical emission spectroscopy as well as by energy-resolved ion mass spectroscopy. The optical spectra showed the contribution of self-sputtering and the portion of metal ions rising with elapsing time during the pulse. Measurement of ion energy distribution functions of different species mostly revealed a low (below 30eV) and a high (around 100eV) energy part. Moreover, the portion of singly and doubly charged target ions is increased with the pulsed discharge current. Deposited layers show a dense, fine-grained structure, indicating a high degree of ionization of the layer-forming particles.

Thermal stability of nanoscale metallic multilayers

Metallic nanolayered thin films/foils, in particular Ni/Al multilayers, have been used to promote joining. The objective of this work is to evaluate the thermal stability of nanoscale metallic multilayers with potential for joining applications. Multilayers thin films with low (Ti/Al and Ni/Ti), medium (Ni/Al) and high (Pd/Al) enthalpies of exothermic reaction were prepared by dual cathode magnetron sputtering. Their thermal stability was studied by: i) differential scanning calorimetry combined with X-ray diffraction (XRD), ii) in-situ XRD using cobalt radiation, and iii) in-situ transmission electron microscopy. It was possible to detect traces of intermetallic or amorphous phases in the as-deposited short period (bilayer thickness) multilayers, except for the Ti/Al films where no reaction products that might be formed during deposition were identified. For short periods (below 20nm) the equilibrium phases are directly achieved upon annealing, whereas for higher periods intermediate trialuminide phases are present for Ti/Al and Ni/Al multilayers. The formation of B2-NiTi from Ni/Ti multilayers occurs without the formation of intermediate phases. On the contrary, for the Pd–Al system the formation of intermediate phases was never avoided.The viability of nanoscale multilayers as “filler” materials for joining macro or microparts/devices was demonstrated.

Chemical vapor deposition of a-CNx:H films for electron field emission using band supermagnetron plasma

A supermagnetron plasma apparatus with two band magnetron cathodes, which can form uniform magnetron plasma under a stationary magnetic field (about 160 G), was used to deposit a-CNx:H films at N2 gas concentrations of 0 and 70%. A high deposition rate of about 85±5 nm/min was obtained at a low dc self-bias voltage, between -20 and -62 V. The optical band gap could be controlled between 1.1 and 3.8 eV. The double-layer a-CNx:H films with optical band gaps of 2.2 eV (upper layer; N2 0%) and 1.5 eV (lower layer; N2 70%) formed on p-Si substrate showed a low-threshold-emission electric field of 9 V/μm.

Corrosion Resistance of CrSiN Coatings by Cathodic Arc Deposition with Different Arc Currents

Bipolar plate with multiple functions is one of the essential components of the PEMFC (Proton Exchange Membrane Fuel Cells) stacks. Recently, metallic bipolar plates, particularly different grades of stainless steels, have been increasingly considered due to relatively low cost, good corrosion resistance, sufficient stiffness and excellent flexibility in thin forms, and easy manufacturability [1-3]. However, the major concerns with the use of stainless steel alloys as bipolar plates are their corrosion resistance and interfacial electrical resistance under long operation conditions. Development of advanced ternary nitride coatings such as chromium silicon nitride (CrSiN) has attracted significant industrial interest in recent years [4-11]. Si addition of CrN to form CrSiN films were prepared by cathode arc ion deposition technique and magnetron sputter technique, in order to improve the characterizations of the coatings from structure to corrosion behaviors. It is reported that with the additional element of Si, the hardness and corrosion resistance of the CrSiN coatings can be greatly improved compared to that of the CrN coating. A direct link between the microstructure and mechanical properties of CrSiN coatings with varying Si contents was established [8]. With increasing Si content, the structure of CrSiN coating exhibited the transformation from a columnar-grained structure to a nanocomposite structure, consisting of CrN nanocrystallites embedded in an amorphous matrix. A maximum hardness of 26.6 GPa was found for CrSiN coating with Si content of about 6.7 at.%, while that of pure CrN was 19.4 GPa [6]. Up to now, the CrSiN is yet thoroughly investigated.

The Magnetized Plasma Effect on Cathode Fall Thickness for Helium Gas Discharge

Our previous study showed that the thickness of the cathode fall region in magnetized DC argon plasma was about 3.3mm has been investigated using two different methods, namely: the axial potential distribution and the current density distribution along the glow discharge regions. The present study demonstrates the same measurements but carried out for Helium gas discharge at the edge and center of the cathode surface for the same characteristic of the DC (cold cathode) magnetron sputtering unit. The Ia–Va characteristic curves of the glow discharge and the axial potential distribution and the current density distribution have been investigated. Under the influence of magnetic field, the thickness of the cathode fall region for he discharge is about 2.5mm for the two methods in pressure (P) range of 1-4mbar. Apparently for helium gas discharge, a reduction of the cathode fall thickness (about 20%) has been found in the presence of a magnetic field at the center of the cathode and (about 37%) at the edge, furthermore stronger electric field at the edge of the cathode fall, and hence high rates of sputtering are expected. Keyword: DC glow discharge; cathode fall thickness; helium gas discharge; magnetic field PACS number; 52.25.Xz. Original Research Article Physical Science International Journal, 4(8): , 2014 1089

Determination of cathode fall thickness in magnetized dc plasma for argon gas discharge

The thickness of the cathode fall region (dc) in magnetized dc argon plasma has been investigated using two different methods, namely the axial potential distribution and the current density distribution along the glow discharge regions. The measurements have been carried out at the edge and center of the cathode surface. Dc (cold cathode) magnetron sputtering unit has been used. The radial and axial distributions of the magnetic field B, the Ia–Va characteristic curves of the glow discharge and the axial potential distribution and the current density distribution have been investigated. The thickness of the cathode fall region was between 2 and 3.3 mm for the two methods in pressure (P) range of 0.53–4 mbar. It is concluded that a noticeable reduction of the cathode fall thickness (about 33%) has been found in the presence of a magnetic field and at the center of the cathode and stronger electric field at the edge of the cathode fall, and hence high rates of sputtering are expected.

Rarefaction windows in a high-power impulse magnetron sputtering plasma

The velocity distribution function of the sputtered particles in the direction parallel to the planar magnetron cathode is studied by spatially- and time-resolved laser-induced fluorescence spectroscopy in a short-duration (20 μs) high-power impulse magnetron sputtering discharge. The experimental evidence for the neutral and ionized sputtered particles to have a constant (saturated) velocity at the end of the plasma on-time is demonstrated. The velocity component parallel to the target surface reaches the values of about 5 km/s for Ti atoms and ions, which is higher that the values typically measured in the direct current sputtering discharges before. The results point out on the presence of a strong gas rarefaction significantly reducing the sputtered particles energy dissipation during a certain time interval at the end of the plasma pulse, referred to as “rarefaction window” in this work. The obtained results agree with and essentially clarify the dynamics of HiPIMS discharge studied during the plasma off-time previously in the work: N. Britun, Appl. Phys. Lett. 99, 131504 (2011).

Deposition of hematite Fe2O3 thin film by DC pulsed magnetron and DC pulsed hollow cathode sputtering system

Semiconducting hematite Fe2O3 thin films were fabricated by means of reactive sputtering in a high power DC pulsed magnetron (HIPIMS) and in a DC pulsed hollow cathode plasma jet sputtering system. Fused silica slides (quartz) were used as substrates. Both plasma processes were monitored with the help of a quartz crystal monitor (QCM) that was also fitted with magnetic field electron suppression filter and biased collecting electrode. This set up measured the deposition rate and the ratio of ionized to neutral fluxes of depositing particles on the substrate during the coating process. The deposition methods were compared in terms of the properties of produced films such as crystalline structure, optical absorption and surface topography. The as-deposited hematite Fe2O3 thin films (without annealing) and after their thermal treatment (with annealing) were examined.

Magnetic dipole discharges. III. Instabilities

Instabilities in a cross-field discharge around a permanent magnet have been investigated. The permanent magnet serves as a cold cathode and the chamber wall as an anode. The magnet is biased strongly negative and emits secondary electrons due to impact of energetic ions. The electrons outside the sheath are confined by the strong dipolar magnetic field and by the ion-rich sheath surrounding the magnet. The electron energy peaks in the equatorial plane where most ionization occurs and the ions are trapped in a negative potential well. The discharge mechanism is the same as that of cylindrical and planar magnetrons, but here extended to a 3-D cathode geometry using a single dipole magnet. While the basic properties of the discharge are presented in a companion paper, the present focus is on various observed instabilities. The first is an ion sheath instability which oscillates the plasma potential outside the sheath below the ion plasma frequency. It arises in ion-rich sheaths with low electron supply, which is the case for low secondary emission yields. Sheath oscillations modulate the discharge current creating oscillating magnetic fields. The second instability is current-driven ion sound turbulence due to counter-streaming electrons and ions. The fluctuations have a broad spectrum and short correlation lengths in all directions. The third type of fluctuations is spiky potential and current oscillations in high density discharges. These appear to be due to unstable emission properties of the magnetron cathode.

Investigation of reactive HiPIMS + MF sputtering of TiO2 crystalline thin films

A hybrid high-power impulse magnetron sputtering (HiPIMS)+mid-frequency (MF) magnetron sputtering system was used for the deposition of crystalline TiO2 thin films at a low substrate temperature. Ion velocity distribution functions (IVDFs) were measured in a pulsed magnetron discharge at substrate positions depending on the type of plasma excitation and on the working gas mixtures. Several different pulsed discharge configurations were used: (i) HiPIMS, (ii) pulsed bipolar MF with frequency 350kHz and (iii) both HiPIMS+MF connected in parallel to the magnetron cathode. The timing of HiPIMS excitation was set to period time T=10ms with “ON” time TON=100μs. Ti targets were sputtered in three different types of atmospheres: (i) inert pure Ar, (ii) a reactive mixture of Ar+O2 and (iii) a reactive mixture of Ar+O2+N2 with a constant gas pressure p=1Pa. All IVDFs were measured using a time-resolved retarding field energy analyzer (RFEA) located in the substrate position. TiO2 thin films were deposited under identical experimental conditions on silica (SiO2) glass substrate, glass with an indium tin oxide (ITO) electrode and polycarbonate polymer foil. The thin film properties are discussed with respect to the measured plasma parameters. It is shown that the combination of HiPIMS+MF excitation in a reactive atmosphere effectively reduces the delay between the edge of cathode voltage and current onset. The highest ion energy was reached in the case of an inert Ar atmosphere due to the highest ratio of fast Ti+ ions in the overall ion flux. All TiO2 thin films deposited in reactive atmospheres formed pure rutile phase regardless of the excitation mode; however, those films deposited by a HiPIMS+MF excitation mode exhibited the greatest ability to produce a photocurrent. Furthermore, HiPIMS+MF was the best setting for the deposition of crystalline TiO2 on polycarbonate foil because of the low heating flux on the substrate and suitable plasma parameters leading to the formation of the rutile phase.

Optimization of the Heat Treatment and Tribological Properties of 2024 and 7075 Aluminium Alloys

This paper describes two stages of optimization of the properties of 2024 and 7075 aluminium alloys, in particular their resistance to pitting by first T6, T6I6 or T6I4 treatment, and second increase its tribological properties by depositing by RF PACVD method a gradient coating of high adhesion to the substrate. Quantitative microstructural characteristics reveals that it is possible to increase hardness (up to 190HV for 7075 alloy) with relatively high yield strength (520 MPa) and high ultimate elongation (about 20%) by optimizing dispersion of precipitates using two-stage artificial aging process. Next to eliminate forming of thin Al2O3 layer with relatively poor adhesion to the aluminium substrate, gradient a-C: H/Ti layers synthesis hybrid plasma chemical RF PACVD reactor equipped with pulsed magnetron sputtering system was used. Using such configuration enables forming a thick and highly adherent diamond-like carbon layer on aluminium surface with low coefficient of friction (0.05), at a substrate temperature below 470K. Due to application of Ti magnetron cathode it was possible to improve the adhesion strength up to 30mN of diamond-like carbon layer to the covered substrate. Influence of deposition parameters on microhardness profile as well as adhesion and morphology were determined by nanotest and AFM, respectively.

Resonant optical absorption spectroscopy of Ce

Resonant optical absorption of ground state Ce atoms is demonstrated. Ce I resonant emission line at 461.05 nm (Aij = 28 × 108 s−1) corresponding to the transition 4f5d6s2–4f2(1G)5d (2I)6s is utilized. In a magnetron sputtering discharge used as an atomic source, the absolute densities of atomic ground state Ce sputtered in pure Ar and in Ar–O2 (oxidized magnetron cathode) gas mixtures are found to be nearly 2 × 108 cm−3 (pure Ar) and 1 × 107 cm−3 (Ar + O2). The phenomena inherent in reactive sputtering, such as the non-oxidized–oxidized regime transition and the hysteresis of the transition point, are detected. The obtained data are compared with the existing results of a similar absorption analysis performed in the Ti dc magnetron discharges. The discrepancies in the obtained Ce and Ti absolute ground state densities are analysed.

Measuring the energy flux at the substrate position during magnetron sputter deposition processes

In this work, the energetic conditions at the substrate were investigated in dc magnetron sputtering (DCMS), pulsed dc magnetron sputtering (pDCMS), and high power impulse magnetron sputtering (HiPIMS) discharges by means of an energy flux diagnostic based on a thermopile sensor, the probe being set at the substrate position. Measurements were performed in front of a titanium target for a highly unbalanced magnetic field configuration. The average power was always kept to 400 W and the probe was at the floating potential. Variation of the energy flux against the pulse peak power in HiPIMS was first investigated. It was demonstrated that the energy per deposited titanium atom is the highest for short pulses (5 μs) high pulse peak power (39 kW), as in this case, the ion production is efficient and the deposition rate is reduced by self-sputtering. As the argon pressure is increased, the energy deposition is reduced as the probability of scattering in the gas phase is increased. In the case of the HiPIMS discharge run at moderate peak power density (10 kW), the energy per deposited atom was found to be lower than the one measured for DCMS and pDCMS discharges. In these conditions, the HiPIMS discharge could be characterized as soft and close to a pulsed DCMS discharge run at very low duty cycle. For the sake of comparison, measurements were also carried out in DCMS mode with a balanced magnetron cathode, in the same working conditions of pressure and power. The energy flux at the substrate is significantly increased as the discharge is generated in an unbalanced field.

Deposition of a-CN<sub>x</sub>:H Films Using Uniform Supermagnetron Plasma under a Stationary Magnet Field

By generating closed-loop electron E × B drift over the front and back surface of a band magnetron cathode, a uniform magnetron plasma can be formed over the front surface. Here, we attempted to generate a uniform supermagnetron plasma under a stationary magnetic field by situating two such band magnetron cathodes face-to-face in parallel. Performing uniform supermagnetron plasma chemical vapor deposition (CVD) with tetraethylorthosilicate (TEOS)/O2 CVD, SiO2 films with good uniformity (±5%) at the central region of the cathode could be achieved under a stationary magnetic field of about 160 G. Using this supermagnetron plasma CVD apparatus, a-CNx:H films were then deposited to investigate their characteristics using isobutane (i-C4H10)/N2 mixed gases. A relatively high deposition rate of about 100 nm/min was obtained. The a-CNx:H films obtained had a hardness of about 25 GPa, higher than that of glass (22 GPa).

From DLC to Si-DLC based layer systems with optimized properties for tribological applications

Diamond-like carbon (DLC) coatings are used in many industrial applications like valvetrain-, fuel injection- and piston-systems. For DLC (a-C:H) coatings, prepared by a magnetron based technique using graphite targets, high indentation hardness values of more than 40GPa were achieved. The wear resistance, the microhardness and the coefficient of friction are shown as a function of the hydrogen concentration in the coatings. In order to reduce the coefficient of friction even more and to increase the operational temperature of the coatings from about 350°C for DLC to near 500°C, a new Si-DLC (a-C:H:Si) based layer system was developed using a special magnetron sputter target configuration. This Si-DLC based layer system combines the benefits of a reduced coefficient of friction with a high wear resistance. The DC magnetron cathode based production method allows the deposition of Si-DLC coatings in a wide range of compositions with 4 to 40at.% Si at low hydrogen contents down to 5at.%. These new Si-DLC based coatings with a silicon concentration around 25at.% Si exhibited under dry conditions friction coefficients with only the half of the value of pure a-C:H. This is rather promising for present and future industrial applications.

The effect of addition of Al in ZrO2 thin film on its resistance to cracking

The paper reports on the structure, mechanical and optical properties of sputtered Zr–Al–O films. The Zr–Al–O films with Zr/Al>1 and Zr/Al<1 were prepared by a reactive sputtering using ac pulse dual magnetrons. The magnetrons were equipped with a target composed of Al plate (∅=50mm) fixed to the magnetron cathode by a Zr fixing ring with inner diameter ∅in. The content of Al in the Zr–Al–O film was controlled by ∅in. It makes possible to control effectively the structure of the Zr–Al–O film determined by a mixture of the crystalline ZrO2 phase and the amorphous Al2O3 phase. The effect of Al content on the structure, mechanical and optical properties of the Zr–Al–O film is investigated in detail. It was found that (i) the Zr–Al–O films with Zr/Al<1 are X-ray amorphous and exhibit low hardness (H≤13GPa), an effective Young's modulus E⁎ resulting in a low H/E⁎<0.1 ratio and low elastic recovery We≤60 and (ii) the Zr–Al–O films with Zr/Al>1 are crystalline and exhibit high hardness (H=18 to 19GPa), an E⁎ satisfying a high H/E⁎≥0.1 ratio, high We up to 78% and strongly enhanced resistance to cracking during bending even for thick films up to 5μm.