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The time-dependent plasma discharge ionization region model (IRM) has been under continuous development during the past decade and used in several studies of the ionization region of high-power impulse magnetron sputtering (HiPIMS) discharges. In the present work, a complete description of the most recent version of the IRM is given, which includes improvements, such as allowing for returning of the working gas atoms from the target, a separate treatment of hot secondary electrons, addition of doubly charged metal ions, etc. To show the general applicability of the IRM, two different HiPIMS discharges are investigated. The first set concerns 400 mu s long discharge pulses applied to an Al target in an Ar atmosphere at 1.8 Pa. The second set focuses on 100 mu s long discharge pulses applied to a Ti target in an Ar atmosphere at 0.54 Pa, and explores the effects of varying the magnetic field strength. The model results show that Al2+-ions contribute negligibly to the production of secondary electrons, while Ti2+-ions effectively contribute to the production of secondary electrons. Similarly, the model results show that for an argon discharge with Al target the contribution of Al+-ions to the discharge current at the target surface is over 90% at 800 V. However, at 400 V the Al+-ions and Ar+-ions contribute roughly equally to the discharge current in the initial peak, while in the plateau region Ar+-ions contribute to roughly 2/3 of the current. For high currents the discharge with Al target develops almost pure self-sputter recycling, while the discharge with Ti target exhibits close to a 50/50 combination of self-sputter recycling and working gas-recycling. For a Ti target, a self-sputter yield significantly below unity makes working gas-recycling necessary at high currents. For the discharge with Ti target, a decrease in the B-field strength, resulted in a corresponding stepwise increase in the discharge resistivity., Funding Agencies|Icelandic Research Fund [130029]; Swedish Government Agency for Innovation Systems (VINNOVA) [2014-04876]

The combined processes of self-sputter (SS)-recycling and process gas recycling in high power impulse magnetron sputtering (HiPIMS) discharges are analyzed using the generalized recycling model (GRM). The study uses experimental data from discharges with current densities from the direct current magnetron sputtering range to the HiPIMS range, and using targets with self-sputter yields Y-SS from approximate to 0.1 to 2.6. The GRM analysis reveals that, above a critical current density of the order of J(crit) approximate to 0.2 A cm(-2), a combination of self-sputter recycling and gas-recycling is generally the case. The relative contributions of these recycling mechanisms, in turn, influence both the electron energy distribution and the stability of the discharges. For high self-sputter yields, above Y-SS approximate to 1, the discharges become dominated by SS-recycling, contain few hot secondary electrons from sheath energization, and have a relatively low electron temperature T-e. Here, stable plateau values of the discharge current develop during long pulses, and these values increase monotonically with the applied voltage. For low self-sputter yields, below Y-SS approximate to 0.2, the discharges above J(crit) are dominated by process gas recycling, have a significant sheath energization of secondary electrons and a higher T-e, and the current evolution is generally less stable. For intermediate values of YSS the discharge character gradually shifts between these two types. All of these discharges can, at sufficiently high discharge voltage, give currents that increase rapidly in time. For such cases we propose that a distinction should be made between unlimited runaway and limited runaway: in unlimited runaway the current can, in principle, increase without a limit for a fixed discharge voltage, while in limited runaway it can only grow towards finite, albeit very high, levels. For unlimited runway Y-SS amp;gt; 1 is found to be a necessary criterion, independent, Funding Agencies|Svensk-Franska Stiftelsen; Icelandic Research Fund [130029]; Swedish Government Agency for Innovation Systems (VINNOVA) [2014-04876]

Sustaining a plasma in a magnetron discharge requires energization of the plasma electrons. In this work, Ohmic heating of electrons outside the cathode sheath is demonstrated to be typically of the same order as sheath energization, and a simple physical explanation is given. We propose a generalized Thornton equation that includes both sheath energization and Ohmic heating of electrons. The secondary electron emission yield gamma(SE) is identified as the key parameter determining the relative importance of the two processes. For a conventional 5 cm diameter planar dc magnetron, Ohmic heating is found to be more important than sheath energization for secondary electron emission yields below around 0.1., Funding Agencies|Swedish Research Council (VR) [621-2014-4882]; Icelandic Research Fund [130029]; Swedish Government Agency for Innovation Systems (VINNOVA) [2014-04876]

A new reactive ionization region model (R-IRM) is developed to describe the reactive Ar/O-2 high power impulse magnetron sputtering (HiPIMS) discharge with a titanium target. It is then applied to study the temporal behavior of the discharge plasma parameters such as electron density, the neutral and ion composition, the ionization fraction of the sputtered vapor, the oxygen dissociation fraction, and the composition of the discharge current. We study and compare the discharge properties when the discharge is operated in the two well established operating modes, the metal mode and the poisoned mode. Experimentally, it is found that in the metal mode the discharge current waveform displays a typical non-reactive evolution, while in the poisoned mode the discharge current waveform becomes distinctly triangular and the current increases significantly. Using the R-IRM we explore the current increase and find that when the discharge is operated in the metal mode Ar+ and Ti+ -ions contribute most significantly (roughly equal amounts) to the discharge current while in the poisoned mode the Ar+ -ions contribute most significantly to the discharge current and the contribution of O+ -ions, Ti+ -ions, and secondary electron emission is much smaller. Furthermore, we find that recycling of atoms coming from the target, that are subsequently ionized, is required for the current generation in both modes of operation. From the R-IRM results it is found that in the metal mode self-sputter recycling dominates and in the poisoned mode working gas recycling dominates. We also show that working gas recycling can lead to very high discharge currents but never to a runaway. It is concluded that the dominating type of recycling determines the discharge current waveform., Funding Agencies|Icelandic Research Fund [130029]; Swedish Government Agency for Innovation Systems (VINNOVA) [2014-04876]

We use an ionization region model to explore the ionization processes in the high power impulse magnetron sputtering (HiPIMS) discharge in argon with a titanium target. In conventional dc magnetron sputtering (dcMS), stepwise ionization can be an important route for ionization of the argon gas. However, in the HiPIMS discharge stepwise ionization is found to be negligible during the breakdown phase of the HiPIMS pulse and becomes significant (but never dominating) only later in the pulse. For the sputtered species, Penning ionization can be a significant ionization mechanism in the dcMS discharges, while in the HiPIMS discharge Penning ionization is always negligible as compared to electron impact ionization. The main reasons for these differences are a higher plasma density in the HiPIMS discharge, and a higher electron temperature. Furthermore, we explore the ionization fraction and the ionized flux fraction of the sputtered vapor and compare with recent experimental work. (C) 2015 AIP Publishing LLC., Funding Agencies|Icelandic Research Fund [130029-053]; Swedish Government Agency for Innovation Systems (VINNOVA) [2014-04876]; Belgian Government through the Pole dAttraction Interuniversitaire (PAI) [P7/34]

The growth of ultra-thin TiN films on single-crystalline MgO(100) substrates by high power impulse magnetron sputtering (HiPIMS) was studied for growth temperatures ranging from 35 degrees C to 600 degrees C. X-ray analysis showed that the films had a textured poly-crystalline structure. Films grown by dc magnetron sputtering (dcMS) were epitaxial at the higher growth temperatures. In-situ resistance measurements, during growth, revealed the coalescence thickness and film continuity thickness. The film grown by HiPIMS at room temperature coalesced at 1.2 +/- 0.1 nm and became structurally continuous at 2.67 +/- 0.15 nm. At 600 degrees C, the coalescence and continuity thicknesses decreased to 0.56 +/- 0.05 nm and 0.82 +/- 0.05 nm, respectively. X-ray reflectivity measurements revealed that the growth rate of the films was roughly constant for all growth temperatures. The film density increased slightly with growth temperature up to 5.3 g/cm(3) at 600 degrees C and the surface roughness of the films decreased from 1 nm to 0.3 nm while the growth temperature increased from 35 degrees C to 600 degrees C. Grazing incident X-ray diffraction measurements showed the presence of [111], [200] and [220] crystallites at all growth temperatures. The smallest [200] and [220] grain sizes appeared at 100 degrees C while the [200] grain size increased by increasing the growth temperature.

Resonant photon tunneling was investigated experimentally in multilayer structures containing a high-contrast (TiO2/SiO2) Bragg mirror capped with a semitransparent gold film. Transmission via a fundamental cavity resonance was compared with transmission via the Tamm plasmon polariton resonance that appears at the interface between a metal film and a one-dimensional photonic bandgap structure. The Tamm-plasmon-mediated transmission exhibits a smaller dependence on the angle and polarization of the incident light for similar values of peak transmission, resonance wavelength, and finesse. Implications for transparent electrical contacts based on resonant tunneling structures are discussed. (C) 2012 Optical Society of America

The high power impulse magnetron sputtering (HiPIMS) discharge is a recent addition to plasma based sputtering technology. In HiPIMS, high power is applied to the magnetron target in unipolar pulses at low duty cycle and low repetition frequency while keeping the average power about 2 orders of magnitude lower than the peak power. This results in a high plasma density, and high ionization fraction of the sputtered vapor, which allows better control of the film growth by controlling the energy and direction of the deposition species. This is a significant advantage over conventional dc magnetron sputtering where the sputtered vapor consists mainly of neutral species. The HiPIMS discharge is now an established ionized physical vapor deposition technique, which is easily scalable and has been successfully introduced into various industrial applications. The authors give an overview of the development of the HiPIMS discharge, and the underlying mechanisms that dictate the discharge properties. First, an introduction to the magnetron sputtering discharge and its various configurations and modifications is given. Then the development and properties of the high power pulsed power supply are discussed, followed by an overview of the measured plasma parameters in the HiPIMS discharge, the electron energy and density, the ion energy, ion flux and plasma composition, and a discussion on the deposition rate. Finally, some of the models that have been developed to gain understanding of the discharge processes are reviewed, including the phenomenological material pathway model, and the ionization region model., QC 20120619

Thin TiN films were grown on SiO(2) by reactive high power impulse magnetron sputtering (HiPIMS) at a range of temperatures from 45 to 600 degrees C. The film properties were compared to films grown by conventional dc magnetron sputtering (dcMS) at similar conditions. Structural characterization was carried out using X-ray diffraction and reflection methods. The HiPIMS process produces denser films at lower growth temperature than does dcMS. Furthermore, the surface is much smoother for films grown by the HiPIMS process. The [200] grain size increases monotonically with increased growth temperature, whereas the size of the [111] oriented grains decreases to a minimum for a growth temperature of 400 degrees C after which it starts to increase with growth temperature. The [200] crystallites are smaller than the [111] crystallites for all growth temperatures. The grain sizes of both orientations are smaller in HiPIMS grown films than in dcMS grown films., Funding Agencies|University of Iceland|072105003

The temporal variation of the electron energy distribution function (EEDF) was measured with a Langmuir probe in a high power impulse magnetron sputtering (HiPIMS) discharge at 3 and 20 mTorr pressures. In the HiPIMS discharge a high power pulse is applied to a planar magnetron giving a high electron density and highly ionized sputtered vapor. The measured EEDF is Maxwellian-like during the pulse; it is broader for lower discharge pressure and it becomes narrower as the pulse progresses. This indicates that the plasma cools as the pulse progresses, probably due to high metal content of the discharge., Original Publication: J T Gudmundsson, P. Sigurjonsson, Petter Larsson, Daniel Lundin and Ulf Helmersson, On the electron energy in the high power impulse magnetron sputtering discharge, 2009, JOURNAL OF APPLIED PHYSICS, (105), 12, 123302. http://dx.doi.org/10.1063/1.3151953 Copyright: American Institute of Physics http://www.aip.org

We describe a versatile three gun magnetron sputtering system with a custom made sample holder for in situ electrical resistance measurements, both during film growth and ambient changes on film electrical properties. The sample holder allows for the preparation of patterned thin film structures, using up to five different shadow masks without breaking vacuum. We show how the system is used to monitor the electrical resistance of thin metallic films during growth and to study the thermodynamics of hydrogen uptake in metallic thin films. Furthermore, we demonstrate the growth of thin film capacitors, where patterned films are created using shadow masks., QC 20110706

The energy distribution of sputtered and ionized metal atoms as well as ions from the sputtering gas is reported for a high power impulse magnetron sputtering (HIPIMS) discharge. High power pulses were applied to a conventional planar circular magnetron Ti target. The peak power on the target surface was 1-2 kW/cm(2) with a duty factor of about 0.5%. Time resolved, and time averaged ion energy distributions were recorded with an energy resolving quadrupole mass spectrometer. The ion energy distributions recorded for the HIPIMS discharge are broader with maximum detected energy of 100 eV and contain a larger fraction of highly energetic ions (about 50% with E-i > 20 eV) as compared to a conventional direct current magnetron sputtering discharge. The composition of the ion flux was also determined, and reveals a high metal fraction. During the most intense moment of the discharge, the ionic flux consisted of approximately 50% Ti1+, 24% Ti2+, 23% Ar1+, and 3% Ar2+ ions., QC 20100525

The growth of ultra-thin, lattice matched, Cr0.7Mo0.3 films on an MgO substrate, in a dc magnetron discharge, was investigated by in situ measurements in order to determine the minimum thickness of a continuous layer. The thickness dependence of the resistivity shows a coalescence thickness of less than two monolayers indicating layer by layer growth of the films. We compare the resistivity of the films to a combination of the Fuchs- Sondheimer and the Mayadas-Shatzkes models, assuming a thickness dependence of grain size. The model indicates that grain size increases with increasing growth temperature., QC 20120125. 12th International Conference on Thin Films, BRATISLAVA, SLOVAKIA, SEP 15-20, 2002

QC 20111222

We report on the creation and propagation of ion-acoustic solitary waves in a high power pulsed magnetron sputtering discharge. A dense localized plasma is created by applying high energy pulses (4-12 J) of length; approximate to 70 mu s, at a repetition frequency of 50 pulses per second, to a planar magnetron sputtering source. The temporal behaviour of the electron density, measured by a Langmuir probe, shows solitary waves travelling away from the magnetron target. The velocity of the waves depends on the gas pressure but is roughly independent of the pulse energy., QC 20120102

We have synthesized Ta thin films on Si substrates placed along a wall of a 2-cm-deep and 1-cm-wide trench, using both a mostly neutral Ta flux by conventional dc magnetron sputtering (dcMS) and a mostly ionized Ta flux by high-power pulsed magnetron sputtering (HPPMS). Structure of the grown films was evaluated by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The Ta thin film grown by HPPMS has a smooth surface and a dense crystalline structure with grains oriented perpendicular to the substrate surface, whereas the film grown by dcMS exhibits a rough surface, pores between the grains, and an inclined columnar structure. The improved homogeneity achieved by HPPMS is a direct consequence of the high ion fraction of sputtered species.

We report on electrostatic probe measurements of a high-power pulsed magnetron discharge. Space- and time-dependent characteristics of the plasma parameters are obtained as functions of the process parameters. By applying high-power pulses (peak power of ~0.5 MW), with a pulse-on time of ~100 µs and a repetition frequency of 20 ms, peak electron densities of the order of ~1019 m− 3, i.e. three orders of magnitude higher than for a conventional dc magnetron discharge, are achieved soon after the pulse is switched on. At high sputtering gas pressures (>5 mTorr), a second peak occurs in the electron density curve, hundreds of microseconds after the pulse is switched off. This second peak is mainly due to an ion acoustic wave in the plasma, reflecting off the chamber walls. This is concluded from the time delay between the two peaks in the electron and ion saturation currents, which is shown to be dependent on the chamber dimensions and the sputtering gas composition. Finally, the electron temperature is determined, initially very high but decreasing rapidly as the pulse is turned off. The reduction seen in the electron temperature, close to the etched area of the cathode, is due to cooling by the sputtered metal atoms.

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 1019 m-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.

Poster presentation. QC 20120125

Poster presentation. QC 20120124