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Fundamentals of High Power Impulse Magnetron Sputtering
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics . Linköping University, The Institute of Technology.
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In plasma assisted thin film growth, control over the energy and direction of the incoming species is desired. If the growth species are ionized this can be achieved by the use of a substrate bias or a magnetic field. Ions may be accelerated by an applied potential, whereas neutral particles may not. Thin films grown by ionized physical vapor deposition (I-PVD) have lately shown promising results regarding film structure and adhesion. High power impulse magnetron sputtering (HIPIMS) is a relatively newly developed technique, which relies on the creation of a dense plasma in front of the sputtering target to produce a large fraction of ions of the sputtered material. In HIPIMS, high power pulses with a length of ~100 μs are applied to a conventional planar magnetron. The highly energetic nature of the discharge, which involves power densities of several kW/cm2, creates a dense plasma in front of the target, which allows for a large fraction of the sputtered material to be ionized.

The work presented in this thesis involves plasma analysis using electrostatic probes, optical emission spectroscopy (OES), magnetic probes, energy resolved mass spectrometry, and other fundamental observation techniques. These techniques used together are powerful plasma analysis tools, and used together give a good overview of the plasma properties is achieved.

from the erosion zone of the magnetron. The peak plasma density during the active cycle of the discharge exceeds 1019 electrons/m3. The expanding plasma is reflected by the chamber wall back into the center part of the chamber, resulting in a second density peak several hundreds of μs after the pulse is turned off.

Optical emission spectroscopy (OES) measurements of the plasma indicate that the degree of ionization of sputtered Ti is very high, over 90 % in the peak of the pulse. Even at relatively low applied target power (~200 W/cm2 peak power) the recorded spectrum is totally dominated by radiation from ions. The recorded HIPIMS spectra were compared to a spectrum taken from a DC magnetron discharge, showing a completely different appearance.

Magnetic field measurements performed with a coil type probe show significant deformation in the magnetic field of the magnetrons during the pulse. Spatially resolved measurements show evidence of a dense azimuthally E×B drifting current. Circulating currents mainly flow within 2 away cm from the target surface in an early part of the pulse, to later diffuse axially into the chamber and decrease in intensity. We record peak current densities of the E×B drift to be of the order of 105 A/m2.

A mass spectrometry (MS) study of the plasma reveals that the HIPIMS discharge contains a larger fraction of highly energetic ions as compared to the continuous DC discharge. Especially ions of the target material are more energetic. Time resolved studies show broad distributions of ion energies in the early stage of the discharge, which quickly narrows down after pulse switch-off. Ti ions with energies up to 100 eV are detected. The time average plasma contains mainly low energy Ar ions, but during the active phase of the discharge, the plasma is highly metallic. Shortly after pulse switch-on, the peak value of the Ti1+/Ar1+ ratio is over 2. The HIPIMS discharge also contains a significant amount of doubly charged ions.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi , 2006.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1014
Keyword [en]
Plasma, Pulsed plasma, High Power Pulsed Magnetron Sputtering, Plasma Characterization
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-7359ISBN: 91-85523-96-8 (print)OAI: oai:DiVA.org:liu-7359DiVA: diva2:22370
Public defence
2006-04-13, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 09:15 (English)
Opponent
Supervisors
Available from: 2006-09-12 Created: 2006-09-12 Last updated: 2013-10-30
List of papers
1. Ionization of sputtered metals in high power pulsed magnetron sputtering
Open this publication in new window or tab >>Ionization of sputtered metals in high power pulsed magnetron sputtering
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2005 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 23, no 1, 18-22 p.Article in journal (Refereed) Published
Abstract [en]

The ion to neutral ratio of the sputtered material have been studied for high power pulsed magnetron sputtering and compared with a continuous direct current (dc) discharge using the same experimental setup except for the power source. Optical emission spectroscopy (OES) was used to study the optical emission from the plasma through a side window. The emission was shown to be dominated by emission from metal ions. The distribution of metal ionized states clearly differed from the distribution of excited states, and we suggest the presence of a hot dense plasma surrounded by a cooler plasma. Sputtered material was ionized close to the target and transported into a cooler plasma region where the emission was also recorded. Assuming a Maxwell–Boltzmann distribution of excited states the emission from the plasma was quantified. This showed that the ionic contribution to the recorded spectrum was over 90% for high pulse powers. Even at relatively low applied pulse powers, the recorded spectra were dominated by emission from ions. OES analysis of the discharge in a continuous dc magnetron discharge was also made, which demonstrated much lower ionization.

Keyword
ionisation, excited states, sputter deposition, plasma deposition, plasma diagnostics
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13974 (URN)10.1116/1.1818135 (DOI)
Available from: 2006-09-12 Created: 2006-09-12 Last updated: 2017-12-13
2. Measurement of the magnetic field change in a pulsed high current magnetron discharge
Open this publication in new window or tab >>Measurement of the magnetic field change in a pulsed high current magnetron discharge
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2004 (English)In: Plasma Sources Science and Technology, ISSN 0963-0252, Vol. 13, no 4, 654-661 p.Article in journal (Refereed) Published
Abstract [en]

In this paper we present a study of how the magnetic field of a circular planar magnetron is affected when it is exposed to a pulsed high current discharge. Spatially resolved magnetic field measurements are presented and the magnetic disturbance is quantified for different process parameters. The magnetic field is severely deformed by the discharge and we record changes of several millitesla, depending on the spatial location of the measurement. The shape of the deformation reveals the presence of azimuthally drifting electrons close to the target surface. Time resolved measurements show a transition between two types of magnetic perturbations. There is an early stage that is in phase with the axial discharge current and a late stage that is not in phase with the discharge current. The later part of the magnetic field deformation is seen as a travelling magnetic wave. We explain the magnetic perturbations by a combination of E × B drifting electrons and currents driven by plasma pressure gradients and the shape of the magnetic field. A plasma pressure wave is also recorded by a single tip Langmuir probe and the velocity (~103 m s−1) of the expanding plasma agrees well with the observed velocity of the magnetic wave. We note that the axial (discharge) current density is much too high compared to the azimuthal current density to be explained by classical collision terms, and an anomalous charge transport mechanism is required.

National Category
Physical Sciences Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13975 (URN)10.1088/0963-0252/13/4/014 (DOI)
Available from: 2006-09-12 Created: 2006-09-12 Last updated: 2013-10-30
3. Spatial electron density distribution in a high-power pulsed magnetron discharge
Open this publication in new window or tab >>Spatial electron density distribution in a high-power pulsed magnetron discharge
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2005 (English)In: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 33, no 2, 346-347 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
magnetron sputtering, plasma density, pulsed plasmas, thin film deposition
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13976 (URN)10.1109/TPS.2005.845022 (DOI)
Available from: 2006-09-12 Created: 2006-09-12 Last updated: 2017-12-13
4. The ion energy distributions and ion flux composition from a high power impulse magnetron sputtering discharge
Open this publication in new window or tab >>The ion energy distributions and ion flux composition from a high power impulse magnetron sputtering discharge
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2006 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 515, no 4, 1522-1526 p.Article in journal (Refereed) Published
Abstract [en]

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/cm2 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 Ei > 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.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi, 2006
Keyword
Sputtering, HIPIMS, Mass spectometry, Plasma characterization
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-10448 (URN)10.1016/j.tsf.2006.04.051 (DOI)
Note
Original publication: J. Bohlmark, M. Lattemann, J. T. Gudmundsson, A. P. Ehiasarian, Y. Aranda Gonzalvo, N. Brenning & U. Helmersson, The ion energy distributions and ion flux composition from a high power impulse magnetron sputtering discharg, 2006, Thin Solid Films, (515), 4, 1522-1526. http://dx.doi.org/10.1016/j.tsf.2006.04.051. Copyright: Elsevier B.V., http://www.elsevier.com/Available from: 2007-12-17 Created: 2007-12-17 Last updated: 2017-12-14
5. Investigation of high power impulse magnetron sputtering pretreated interfaces for adhesion enhancement of hard coatings on steel
Open this publication in new window or tab >>Investigation of high power impulse magnetron sputtering pretreated interfaces for adhesion enhancement of hard coatings on steel
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2006 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 200, no 22-23, 6495-6499 p.Article in journal (Refereed) Published
Abstract [en]

In order to improve the adhesion of hard coatings such as CrN, a surface pretreatment by the novel high power impulse magnetron sputtering (HIPIMS) technique followed by reactive unbalanced d.c. magnetron sputtering deposition was performed using a Cr target. The HIPIMS plasma comprising a high metal ion-to-neutral ratio consisting of single- and double-charged metal species identified by mass spectrometry increased the metal ion flux to the substrate. When applying a negative substrate bias Ub the adhesion was enhanced due to sputter cleaning of the surface and metal ion intermixing in the interface region. This intermixing, resulting in a gradual change of the composition, is considered to enhance the adhesion of the hard coatings on steel substrates. The pretreatment was carried out in an inert gas atmosphere at a pressure of pAr = 1 mTorr, the duration was varied between 25 and 75 min, whereas the negative substrate bias was varied between 400 V and 1200 V. The adhesion was found to depend on the substrate bias as well as on the target power and, for low substrate bias, on the duration of the pretreatment. For CrN the critical load of failure determined by scratch test could be increased in comparison to the values reported for specimens pretreated by conventional Ar etching. The influence of the target peak voltage, the substrate bias as well as pretreatment time on the constitution and morphology of the interface after the pretreatment is discussed applying analytical transmission electron microscopy.

Keyword
Ionized PVD, Pulsed magnetron sputtering, Analytical TEM, Adhesion, Ion implantation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-15030 (URN)10.1016/j.surfcoat.2005.11.082 (DOI)
Note
Original publication: M. Lattemann, A.P. Ehiasarian, J. Bohlmark, P.Å.O. Persson and U. Helmersson, Investigation of high power impulse magnetron sputtering pretreated interfaces for adhesion enhancement of hard coatings on steel, 2006, Surface and Coatings Technology, (200), 22-23, 6495-6499. http://dx.doi.org/10.1016/j.surfcoat.2005.11.082. Copyright: Elsevier B.V., http://www.elsevier.com/ Available from: 2008-10-10 Created: 2008-10-10 Last updated: 2017-12-11
6. Guiding the deposition flux in an ionized magnetron discharge
Open this publication in new window or tab >>Guiding the deposition flux in an ionized magnetron discharge
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2006 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 515, no 4, 1928-1931 p.Article in journal (Refereed) Published
Abstract [en]

A study of the ability to control the deposition flux in a high power impulse magnetron sputtering discharge using an external magnetic field is presented in this article. Pulses with peak power of 1.4 kWcm-2 were applied to a conventional planar magnetron equipped with an Al target. The high power creates a high degree of ionization of the sputtered material, which opens for an opportunity to control of the energy and direction of the deposition species. An external magnetic field was created with a current carrying coil placed in front of the target. To measure the distribution of deposition material samples were placed in an array surrounding the target and the depositions were made with and without the external magnetic field. The distribution is significantly changed when the magnetic field is present. An increase of 80 % in deposition rate is observed for the sample placed in the central position (right in front of the target center) and the deposition rate is strongly decreased on samples placed to the side of the target. The measurements were also performed on a conventional direct current magnetron discharge, but no major effect of the magnetic field was observed in that case.

Place, publisher, year, edition, pages
Amsterdam, Netherlands: Elsevier, 2006
Keyword
thin films, sputtering, IPVD, HIPIMS, HPPMS
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-10441 (URN)10.1016/j.tsf.2006.07.183 (DOI)000242931900112 ()
Note

Original publication: J. Bohlmark, M. Östbye, M. Lattemann, H. Ljungcrantz, T. Rosell, and U. Helmersson, Guiding the deposition flux in an ionized magnetron discharge, 2006, Thin Solid Films, (515), 4, 1928-1931. http://dx.doi.org/10.1016/j.tsf.2006.07.183. Copyright: Elsevier B.V., http://www.elsevier.com/

Available from: 2007-12-14 Created: 2007-12-14 Last updated: 2017-12-14

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