Magnetron Magnetic Field Research Articles

On double-layer and reverse discharge creation during long positive voltage pulses in a bipolar HiPIMS discharge

Time-resolved Langmuir probe diagnostics at the discharge centerline and at three distances from the target ( 35mm , 60mm , and 100mm ) was carried out during long positive voltage pulses (a duration of 500μs and a preset positive voltage of 100V ) in bipolar high-power impulse magnetron sputtering of a Ti target (a diameter of 100mm ) using an unbalanced magnetron. Fast-camera spectroscopy imaging recorded light emission from Ar and Ti atoms and singly charged ions during positive voltage pulses. It was found that during the long positive voltage pulse, the floating and the plasma potentials suddenly decrease, which is accompanied by the presence of anode light located on the discharge centerline between the target center and the magnetic null of the magnetron’s magnetic field. These light patterns are related to the ignition of a reverse discharge, which leads to the subsequent rise in the plasma and the floating potentials. The reversed discharge is burning up to the end of the positive voltage pulse, but the plasma and floating potentials have lower values than the values from the initial part of the positive voltage pulse. Secondary electron emission induced by the impinging Ar+ ions to the grounded surfaces in the vicinity of the discharge plasma together with the mirror configuration of the magnetron magnetic field are identified as the probable causes of the charge double-layer structure formation in front of the target and the ignition of the reverse discharge.

Real-time monitoring of plasma synthesis of functional materials by high power impulse magnetron sputtering and other PVD processes: towards a physics-constrained digital twin

Plasma synthesis of thin films by physical vapour deposition (PVD) enables the creation of materials that drive significant innovations in modern life. High value manufacturing demand for tighter quality control and better resource utilisation can be met by a digital twin capable of modelling the deposition process in real time. Optical emission spectroscopy (OES) was combined with process parameters to monitor all stages of both high power impulse magnetron sputtering and conventional magnetron sputtering processes to provide a robust method of determining process repeatability and a reliable means of process control for quality assurance purposes. Strategies and physics-based models for the in-situ real-time monitoring of coating thickness, composition, crystallographic and morphological development for a CrAlYN/CrN nanoscale multilayer film were developed. Equivalents to the ion-to-neutral ratio and metal-to-nitrogen ratios at the substrates were derived from readily available parameters including the optical emission intensities of Cr I, N2 (C–B) and Ar I lines in combination with the plasma diffusivity coefficient obtained from the ratio of substrate and cathode current densities. These optically-derived equivalent parameters identified the deposition flux conditions which trigger the switch of dominant crystallographic texture from (111) to (220) observed in XRD pole figures and the development of coating morphology from faceted to dense for a range of magnetron magnetic field configurations. OES-based strategies were developed to monitor the progress of chamber evacuation, substrate cleaning and preventative chamber wall cleaning to support process optimisation and equipment utilisation. The work paves the way to implementation of machine learning protocols for monitoring and control of these and other processing activities, including coatings development and the use of alternative deposition techniques. The work provides essential elements for the creation of a digital twin of the PVD process to both monitor and predict process outcomes such as film thickness, texture and morphology in real time.

The influence of pressure and magnetic field on the deposition of epitaxial TiBx thin films from DC magnetron sputtering

Magnetron sputter deposition of TiBx thin films from a TiB2 target typically results in highly overstoichiometric films due to differences in sputtered-atom ejection angles and gas-phase scattering during transport to the substrate. This study investigates the effects of the magnetron magnetic field strength at the substrate position and the Ar sputtering pressure on the resulting film composition and crystalline quality. It is shown that the B/Ti atomic ratio can be reduced from 2.7 to 2.1 by increasing the Ar pressure from 5 mTorr to 20 mTorr, a trend consistent with previous work. Despite the use of a relatively high Ar pressure, a change to a stronger outer magnetic pole leads to, dense TiB2.1 films of high crystal quality, as shown by X-ray diffraction, scanning transmission electron microscopy, and specific resistivity of 32 μΩcm. For epitaxial films deposited at 900 °C on Al2O3(001), a TiB2[110]//Al2O3[100] orientational relationship were obtained.

Magnetic control of nonlinear electron resonance heating in a capacitively coupled radio frequency discharge

In magnetized capacitively coupled radio frequency (RF) plasmas operated at low pressure, the magnetic asymmetry effect (MAE) provides the opportunity to control the discharge symmetry, the DC self-bias, and the ion energy distribution functions at boundary surfaces by adjusting a magnetic field, that is oriented parallel to the electrodes, at one electrode, while leaving it constant at the opposite electrode. This effect is caused by the presence of different plasma densities in regions of different magnetic field strength. Here, based on a balanced magnetron magnetic field configuration at the powered electrode, we demonstrate that the magnetic control of the plasma symmetry allows to tailor the generation of high frequency oscillations in the discharge current induced by the self-excitation of the plasma series resonance (PSR) through adjusting the magnetic field adjacent to the powered electrode. Experimental current measurements performed in an argon discharge at 1 Pa as well as results of an equivalent circuit model show that nonlinear electron resonance heating can be switched on and off in this way. Moreover, the self-excitation of the PSR can be shifted in time (within the RF period) and in space (from one electrode to the other) by controlling the discharge symmetry via adjusting the magnetic field.

Effect of magnetic field on the formation of Cu nanoparticles during magnetron sputtering in the gas aggregation cluster source

AbstractReliable production of nanoparticles (NPs) by magnetron sputtering in a gas aggregation source (GAS) is of great interest because of many potential applications. The size, shape, or structure of NPs can be tuned by the operational parameters of the GAS. In this study, fabrication of copper (Cu) NPs is investigated dependent on the magnetron magnetic field (MF)–a not much studied parameter. Decrease of the MF from 83 to 35 mT results in changes in the shape and size distribution of the NPs. MF also strongly affects the NPs deposition rate (DR). Electromagnetic trapping of the NPs in the vicinity of the magnetron target is proposed to be responsible for the changes in DR and polydispersity. The highest DR was reached at 45 mT.

In-flight modification of Ni nanoparticles by tubular magnetron sputtering

A tubular magnetron (TMG) was used for in-flight deposition of Cu over Ni nanoparticles (NPs) pre-synthesized in a planar magnetron-based gas aggregation cluster source. The amount of deposited copper was driven by the magnetron current and magnetic field of the TMG. The structure of the resultant NPs was investigated by transmission electron microscopy (TEM), scanning transmission electron microscopy, x-ray diffraction (XRD) and small angle x-ray scattering. Alloying of Cu and Ni was observed in all the cases, yet with the formation of a copper-enriched shell in the case with higher Cu content. XRD and TEM analyses showed that plasma-NP interactions led to the disappearance of Ni crystal lattice defects. For a certain range of the magnetron currents, spontaneous pulsing of the NPs deposition rate was observed which was accompanied by the changes in the NP size distribution and chemical composition. The phenomenon was attributed to the cycle trapping, growth and release of the NPs inside and from the TMG. Such cycle instabilities led to the formation of NP deposits with high polydispersity.

Optical properties of diamond like carbon films containing copper, grown by high power pulsed magnetron sputtering and direct current magnetron sputtering: Structure and composition effects

In the present study chemical composition, structure and optical properties of hydrogenated diamond like carbon films containing copper (DLC:Cu films) deposited by reactive magnetron sputtering were studied. Different modes of deposition — direct current (DC) sputtering and high power pulsed magnetron sputtering (HIPIMS) as well as two configurations of the magnetron magnetic field (balanced and unbalanced) were applied. X-ray diffractometry, Raman scattering spectroscopy, energy-dispersive X-ray spectroscopy and atomic force microscopy were used to study the structure and composition of the films. It was shown that by using HIPIMS mode contamination of the cathode during the deposition of DLC:Cu films can be suppressed. In all cases oxygen atomic concentration in the films was in 5–10at.% range and it increased with the copper atomic concentration. The highest oxygen content was observed in the films deposited employing low ion/neutral ratio balanced DC magnetron sputtering process. According to the analysis of the parameters of Raman scattering spectra, sp3/sp2 bond ratio decreased with the increase of Cu atomic concentration in the DLC films. Clear dependence of the extinction, absorbance and reflectance spectra on copper atomic concentration in the films was observed independently of the method of deposition. Surface plasmon resonance effect was observed only when Cu atomic concentration in DLC:Cu film was at least 15at.%. The maximum of the surface plasmon resonance peak of the absorbance spectra of DLC:Cu films was in 600–700nm range and redshifted with the increase of Cu amount. The ratio between the intensities of the plasmonic peak and hydrogenated amorphous carbon related peak at ~220nm both in the extinction and absorbance spectra as well as peak to background ratio of DLC:Cu films increased linearly with Cu amount in the investigated 0–40at.% range. Reflectance of the plasmonic DLC:Cu films was in 30–50% range that could be important in practical optical applications of DLC:Cu films.

Deposition rate enhancement in HiPIMS without compromising the ionized fraction of the deposition flux

We systematically investigate and quantify different physical phenomena influencing the deposition rate, aD, of Nb coatings prepared by high power impulse magnetron sputtering (HiPIMS), and propose a straightforward approach for deposition rate enhancement through the control of the magnetron's magnetic field. The magnetic field strength at the target surface, B, of a 50 mm diameter magnetron was controlled by the application of paramagnetic spacers with different thicknesses in between the magnetron surface and the target. We found that lowering B achieved by the application of a 2.8 mm thick spacer led to an increase in aD by a factor of ∼4.5 (from 10.6 to 45.2 nm min−1) when the discharge was operated at a fixed average pulse target power density (2.5 kW cm−2). However, the ionized fraction of the deposition flux onto the substrate was found to be comparable, despite a large difference in B-dependent discharge characteristics (magnetron voltage and discharge current). We show that the decrease in aD commonly observed in HiPIMS (ranging from 33% to 84% in comparison with dc magnetron sputtering in the presented experiments) is governed by different physical processes, depending on the value of B: for high B, the back-attraction of the target ions towards the target is the dominant effect, while for low B the ion back-attraction, the sub-linear dependence of the sputtering yield on the ion energy, and the variation in material transport effects are all important. Finally, we offer a theoretical background for the observed results, demonstrating that the here-presented conclusions may be applicable to HiPIMS discharges using different metal targets and different inert gases.

Voluminous high-density plasma generator based on high-current pulsed magnetron discharge

Results of investigations into the spatial and temporal parameters of the voluminous plasma generated by two high-current pulsed magnetron sputtering systems operating in balanced and unbalanced regimes are presented. It is demonstrated that the plasma filling the vacuum chamber comprises two components: the plasma drifting from the region of magnetron magnetic traps and the plasma generated by oscillating electrons directly in the chamber volume. For the balanced magnetron magnetic field configuration, the plasma in the centre of the vacuum chamber with volume of ~10 L has concentration of (1–2)⋅1013 cm−3 for magnetron discharge current amplitude of 350 A. The application of the unbalanced magnetic field configuration allows the plasma concentration in the central part of the vacuum chamber to be increased to ~6⋅1013 cm−3.

Design and characterization of 2.45 GHz electron cyclotron resonance plasma source with magnetron magnetic field configuration for high flux of hyperthermal neutral beam

A 2.45 GHz electron cyclotron resonance (ECR) source with a magnetron magnetic field configuration was developed to meet the demand of a hyperthermal neutral beam (HNB) flux on a substrate of more than 1x10(15) cm(-2) s(-1) for industrial applications. The parameters of the operating pressure, ion density, electron temperature, and distance between the neutralization plate and the substrate for the HNB source are specified in a theoretical analysis. The electron temperature and the ion density are measured to characterize the ECR HNB source using a Langmuir probe and optical emission spectroscopy. The parameters of the ECR HNB source are in good agreement with the theoretically specified parameters.

Plasma potential measurement in 2.45 GHz electron cyclotron resonance plasma with a magnetron magnetic field configuration

A 2.45 GHz electron cyclotron resonance (ECR) plasma source with a magnetron magnetic field configuration has been developed for the generation of high flux of hyperthermal neutral beams (HNB). The plasma potential in ECR plasma is required to obtain the HNB energy. In this study, the axial profile of the plasma potential was deduced from the ion kinetic energy distribution (IED) which was measured using an ion energy analyzer. It was found that the IED was broadened with a full width half maximum (FWHM), representing the difference between the maximum plasma potential and the minimum plasma potential.

Current Distribution on the Substrate in a Vacuum Arc Deposition Setup

AbstractThe effect of a magnetic field generated by a planar magnetron on the ion current distribution on the substrate has been investigated as a function of the substrate voltage and gas pressure for two configurations of the magnetic field. The probe and the substrate were biased by negative potentials of −60 to −280 V with respect to the grounded anode, in order to collect the saturated ion current and investigate the influence of the magnetron magnetic field on the distribution of the ion flux of the vacuum arc source. It was shown that the planar magnetron placed under the substrate strongly affects the ion current and ion current distribution near the substrate. For a broad pressure range, the maximum ion flux collected by the probe increased by 40%, while the net ion current to the substrate increased by 20%. We have demonstrated that the ion current increased by 18%, and maximum ion current density increased by 40%. The results were explained in terms of the plasma flux interaction with the magnetic field of the magnetron. The setup may be suitable for controlling ion flux density on large substrates.magnified image

Spatial electron density distribution in a high-power pulsed magnetron discharge

The spatial electron density distribution was measured as function of time in a high-power pulsed magnetron discharge. A Langmuir probe was positioned in various positions below the target and the electron density was mapped out. We recorded peak electron densities exceeding 10/sup 19/ m/sup -3/ in a close vicinity of the target. The dynamics of the discharge showed a dense plasma expanding from the "race-track" axially into the vacuum chamber. We also record electrons trapped in a magnetic bottle where the magnetron magnetic field is zero, formed due to the unbalanced magnetron.

Low-energy ion bombardment effects in reactive rf magnetron sputtering of carbon nitride films

Variable unbalanced rf magnetron sputtering of graphite in pure nitrogen and a mixture of nitrogen and helium has been used to prepare carbon nitride films in a wide range of ion bombardment conditions analyzed as to their fluxes and kinetic energies by energy-resolved mass spectrometry and probe measurements. These data were related to the chemical composition, bonding structure, density and Young's modulus of the deposited CN x films which have been studied by several analytical methods. The energy flux density supplied to the growing film by the bombarding positive ions and the bombardment energy per condensing C and N atom were determined to range from below 1×10 −3 to close to 5 Wcm −2 and from about 1 up to 2×10 3 eV, respectively, depending on rf power density, discharge pressure and magnetron magnetic field configuration chosen. With increasing energy flux of the ion bombardment the overall [N]/[C] ratio of the films decreases exponentially from a maximum of about 1 to a final value of nearly 0.3 attributed to a bombardment activated desorption of N atoms as well as to a diminishing formation and/or an increased resputtering of N-H groups. The CN x films were found to consist of an amorphous sp 2/sp 3 hybridized carbon matrix with N substitutions of C atoms and contributions of several C-N and N-H groups. At increasing energy flux density of the ion bombardment the matrix changes from a more graphite-like phase with large sp 2 domains to a predominantly disordered carbon structure. In low-pressure quadrupole magnetic field magnetron sputtering the film density increases with increasing bombardment energy per condensing C and N atom, but remains below that of graphite. This was accompanied by increasing Young's moduli not exceeding 120 GPa.

Radio-frequency-magnetron-sputtered CdS/CdTe solar cells on soda-lime glass

We report the fabrication of an 11.6% efficient, polycrystalline thin-film CdS/CdTe solar cell in which both semiconductor layers were deposited by planar-magnetron-radio-frequency sputtering at 380 °C on commercially available soda-lime float-glass substrates coated with SnO2:F. We show that the magnetron magnetic field is critical to obtaining high cell efficiency. Much stronger photoluminescence and higher electrical conductivity are found in films and cells grown with unbalanced-field magnetrons. The magnetic field dependence is interpreted as arising from the enhanced electron and ion bombardment of the film growth interface when unbalanced magnetrons are used.

Deposition of hard coatings in open magnetic field confined plasma

A d.c. glow discharge deposition system is described which allows the independent control of the substrate current density by using several discharge power supplies. The system consists of a magnetron cathode with permanent magnets and a magnetic coil placed behind the magnetron target, three cages with permanent magnets and an auxiliary anode parallel to the magnetron target surface. The magnetron cathode, auxiliary anode and magnetic cages enclose the deposition volume in which the substrates to be treated are placed. An open geometry magnetic field is obtained in the deposition volume by suitable arrangement of the permanent magnets. The main gas discharge in the system is a balanced magnetron discharge obtained by means of a 20 kW power supply. Three additional power supplies are used to unbalance the magnetron magnetic field by adjusting the magnetic coil current, to bias the substrate and to change the potential of the auxiliary anode. The performance of the deposition system was tested during reactive deposition of TiN coatings on HSS steel substrates.

Electron energy distribution function in DC magnetron axially symmetric discharges: evidence of spatial anisotropy

Experimental measurements of the second derivative d2i/dv2 of the probe current i versus probe voltage v were performed in an axially symmetric magnetron sputtering gas discharge plasma in order to determine the electron energy distribution function. The measurements were performed using a cylindrical Langmuir probe oriented in two directions, along and across the discharge axis. The experiments were carried out at a constant argon gas pressure of 3 mTorr and at a constant discharge current of 1 A to a molybdenum cathode. Three different magnetic field configurations in the discharge region were investigated and these were achieved by superimposing an external magnetic field on the original magnetron magnetic field. By varying the magnetic field distribution and, in particular, the respective axial component of the magnetic induction Bz at the probe position, the second derivative d2i/dv2 was significantly altered. Certain differences in d2i/dv2 were also established with the probe oriented in radial and axial directions. A spherical spatial plasma isotropy of the electron energy distribution function was thus found for the opposed superimposed magnetic field (Bz=-31 G) while for both the original (Bz=36 G) and the supporting (Bz=103 G) magnetic field configurations, a plasma anisotropy was established. The degree of anisotropy was quantified by comparison of the respective average electron energies (E) evaluated for each of the three magnetic field configurations. It was found that assumption of spherical isotropy during determination of the electron energy distribution function leads to overestimation of (E) by up to 10% under the experimental conditions used.

Zero-defect sputter deposition metallization method for high volume manufacturing of grafted multilayer thin film modules

Such products as multichip modules, stripline filters, and thin-film hybrid circuits typically require the metallization of ceramic-based substrates and subsequent dielectric layers such as polyimides and benzocyclobutene. When dry etching processes are employed for the dielectric layers, an additional metallization step is required to serve as the etch mask. Therefore, the need for a high-volume zero-defect metallization technique is apparent. An inline DC magnetron sputter deposition process that provides such a metallization technique is discussed. High equipment reliability (>99% up-time), low defect levels (<10 ppm), and the use of 12-mm targets allowing the metallization of 3000 ft/sup 2/ between cathode changes has been achieved. The system is configured to provide layered metal systems with discrete or phased interfaces. Plasma optimization via real-time magnetron control and magnetic field suppression at the beginning of target life has enabled deposit thickness (and sheet resistivity) variation to be automatically controlled to +or-5% over the 435-in/sup 2/ deposition area throughout the life of the targets.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The influence of discharge current on the intrinsic stress in Mo films deposited using cylindrical and planar magnetron sputtering sources

Previous work has shown that the transition pressure, pt, below which large compressive stresses are found in magnetron sputtered metal films deposited at low T/Tm, increases with the discharge current, at least for the case of cylindrical-post magnetrons with magnetic field configurations generated by magnets mounted within the cathode barrels. This paper reports measurements of the internal stress as a function of discharge current for Mo films deposited using a planar magnetron and also a cylindrical-post magnetron having an externally generated magnetic field which permitted the discharge voltage to be varied independent of the current. At each current, coatings were deposited over a sufficient pressure range to identify pt. Transition pressures, determined by stress, resistivity, and optical reflectance measurements, for both the planar and cylindrical magnetrons, exhibited an increase with discharge current, consistent with the previous work. Reducing the cylindrical magnetron magnetic field to increase the discharge voltage at a fixed current consistently yielded higher pt. Strong correlations were seen between pt and the discharge voltage for both the cylindrical and planar magnetrons. It is concluded that the increase in pt with discharge current is significantly influenced by the accompanying increase in discharge voltage and not associated with the concurrent increase in deposition rate per se.