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An ionization region model for high-power impulse magnetron sputtering discharges
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
Shanghai Jiao Tong University; University of Iceland.ORCID iD: 0000-0002-8153-3209
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
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2011 (English)In: Plasma sources science & technology (Print), ISSN 0963-0252, E-ISSN 1361-6595, Vol. 20, no 6, 065007- p.Article in journal (Refereed) Published
Abstract [en]

A time-dependent plasma discharge model has been developed for the ionization region in a high-power impulse magnetron sputtering (HiPIMS) discharge. It provides a flexible modeling tool to explore, e. g., the temporal variations of the ionized fractions of the working gas and the sputtered vapor, the electron density and temperature, and the gas rarefaction and refill processes. A separation is made between aspects that can be followed with a certain precision, based on known data, such as excitation rates, sputtering and secondary emission yield, and aspects that need to be treated as uncertain and defined by assumptions. The input parameters in the model can be changed to fit different specific applications. Examples of such changes are the gas and target material, the electric pulse forms of current and voltage, and the device geometry. A basic version, ionization region model I, using a thermal electron population, singly charged ions, and ion losses by isotropic diffusion is described here. It is fitted to the experimental data from a HiPIMS discharge in argon operated with 100 mu s long pulses and a 15 cm diameter aluminum target. Already this basic version gives a close fit to the experimentally observed current waveform, and values of electron density n(e), the electron temperature T(e), the degree of gas rarefaction, and the degree of ionization of the sputtered metal that are consistent with experimental data. We take some selected examples to illustrate how the model can be used to throw light on the internal workings of these discharges: the effect of varying power efficiency, the gas rarefaction and refill during a HiPIMS pulse, and the mechanisms determining the electron temperature.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2011. Vol. 20, no 6, 065007- p.
Keyword [en]
GLOBAL-MODEL, ELECTRON-EMISSION, PLASMAS, ARGON, DENSITIES, ALUMINUM, METALS
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-63269DOI: 10.1088/0963-0252/20/6/065007ISI: 000298139300008Scopus ID: 2-s2.0-82755162844OAI: oai:DiVA.org:kth-63269DiVA: diva2:483463
Funder
Swedish Research Council
Note

QC 20120125

Available from: 2012-01-25 Created: 2012-01-23 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Modeling High Power Impulse Magnetron Sputtering Discharges
Open this publication in new window or tab >>Modeling High Power Impulse Magnetron Sputtering Discharges
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

HiPIMS, high power impulse magnetron sputtering, is a promising technology that has attracted a lot of attention ever since its appearance. A time-dependent plasma discharge model has been developed for the ionization region in HiPIMS discharges. As a flexible modeling tool, it can be used to explore the temporal variations of the ionized fractions of the working gas and the sputtered vapor, the electron density and temperature, and the gas rarefaction and refill processes. The model development has proceeded in steps. A basic version IRM I is fitted to the experimental data from a HiPIMS discharge with 100 μs long pulses and an aluminum target. A close fit to the experimental current waveform, and values of density, temperature, gas rarefaction, as well as the degree of ionization shows the validity of the model. Then an improved version is first used for an investigation of reasons for deposition rate loss, and then fitted for another HiPIMS discharge with 400 μs long pulses and an aluminum target to investigate gas rarefaction, degree of ionization, degree of self sputtering, and the loss in deposition rate, respectively. Through these results from the model, we could analyse further the potential distribution and its evolution as well as the possibility of a high deposition rate window to optimize the HiPIMS discharge.

Besides this modeling, measurements of HiPIMS discharges with 100 μs long pulses and a copper target are made and analyzed. A description, based on three different types of current systems during the ignition, transition and steady phase, is used to describe the evolution of the current density distribution in the pulsed plasma. The internal current density ratio is a key transport parameter. It is reported how it varies with space and time, governing the cross-B resistivity and the energy of the charged particles. From the current ratio the electron cross-B transport can be obtained and used as essential input when modeling the axial electric field, governing the back-attraction of ions.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xii, 52 p.
Series
Trita-EE, ISSN 1653-5146 ; 2012:017
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-94002 (URN)
Presentation
2012-05-25, Seminarierummet, Alfvénlaboratoriet, Teknikringen 31, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note
QC 20120504Available from: 2012-05-04 Created: 2012-05-04 Last updated: 2012-05-07Bibliographically approved
2. Modeling and Experimental Studies of High Power Impulse Magnetron Sputtering Discharges
Open this publication in new window or tab >>Modeling and Experimental Studies of High Power Impulse Magnetron Sputtering Discharges
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

HiPIMS, high power impulse magnetron sputtering, is a promising technology that has attracted a lot of attention, ever since it was introduced in 1999. A time-dependent plasma discharge model has been developed for the ionization region (IRM) in HiPIMS discharges. As a flexible modeling tool, it can be used to explore the temporal variations of the ionized fractions of the working gas and the sputtered vapor, the electron density and temperature, the gas rarefaction and refill processes, the heating mechanisms, and the self-sputtering process etc.. The model development has proceeded in steps. A basic version IRM I is fitted to the experimental data from a HiPIMS discharge with 100 μs long pulses and an aluminum target (Paper I). A close fit to the experimental current waveform, and values of density, temperature, gas rarefaction, as well as the degree of ionization shows the general validity of the model. An improved version, IRM II is first used for an investigation of reasons for deposition rate loss in the same discharge (Paper II). This work contains a preliminary analysis of the potential distribution and its evolution as well as the possibility of a high deposition rate window to optimize the HiPIMS discharge. IRM II is then fitted to another HiPIMS discharge with 400 μs long pulses and an aluminum target and used to investigate gas rarefaction, degree of ionization, degree of self-sputtering, and the loss in deposition rate (Paper III). The most complete version, IRM III is also applied to these 400 μs long pulse discharges but in a larger power density range, from the pulsed dcMS range 0.026 kW/up to 3.6 kW/where gas rarefaction and self-sputtering are important processes. It is in Paper IV used to study the Ohmic heating mechanism in the bulk plasma, couple to the potential distribution in the ionization region, and compare the efficiencies of different mechanisms for electron heating and their resulting relative contributions to ionization. Then, in Paper V, the particle balance and discharge characteristics on the road to self-sputtering are studied. We find that a transition to a discharge mode where self-sputtering dominates always happens early, typically one third into the rising flank of an initial current peak. It is not driven by process gas rarefaction, instead gas rarefaction develops when the discharge already is in the self-sputtering regime. The degree of self-sputtering increases with power: at low powers mainly due to an increasing probability of ionization of the sputtered material, and at high powers mainly due to an increasing self-sputter yield in the sheath.

Besides this IRM modeling, the transport of charged particles has been investigated byiv measuring current distributions in HiPIMS discharges with 200 μs long pulses and a copper target (Paper VI). A description, based on three different types of current systems during the ignition, transition and steady state phase, is used to analyze the evolution of the current density distribution in the pulsed plasma. The internal current density ratio (Hall current density divided by discharge current density) is a key transport parameter. It is reported how it varies with space and time, governing the cross-B resistivity and the mobility of the charged particles. From the current ratio, the electron cross-B (Pedersen) conductivity can be obtained and used as essential input when modeling the axial electric field that was the subject of Papers II and IV, and which governs the back-attraction of ions.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xiii, 75 p.
Series
Trita-EE, ISSN 1653-5146 ; 2013:029
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-126264 (URN)978-91-7501-819-5 (ISBN)
Public defence
2013-09-18, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
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Supervisors
Note

QC 20130830

Available from: 2013-08-30 Created: 2013-08-20 Last updated: 2013-11-07Bibliographically approved

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