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On the connection between the self-sputter yield and deposition rate in HiPIMS operation On the connection between the self-sputter yield and deposition rate in HiPIMS operation J. T. Guðmundsson1,2, M. Rudolph3, K. Barynova1, J. Fischer4, S. Suresh Babu1, N. Brenning2,4, M. A. Raadu2, H. Hajihoseini5 and D. Lundin4 1 Science Institute, University of Iceland, Reykjavik, Iceland 2 KTH Royal Institute of Technology, Stockholm, Sweden 3 Leibniz Institute of Surface Engineering (IOM), Leipzig, Germany 4 Plasma and Coatings Physics, Linköping University, Sweden 5 Industrial Focus Group XUV Optics, University of Twente, The Netherlands The 49th International Conference on Metallurgical Coatings and Thin Films (ICMCTF), San Diego, California, May 25., 2023 On the connection between the self-sputter yield and deposition rate in HiPIMS operation Introduction – Magnetron sputtering Gudmundsson and Lundin (2020) in High Power Impulse Magnetron Sputtering Discharge, Elsevier, 2020 Magnetron sputtering has been a highly sucessfull technique that is essential in a number of industrial applications In a high power impulse magnetron sputtering (HiPIMS) the discharge is driven by high power pulses of low repetition frequency, and with low duty cycle This results in high discharge current density, increased electron density, and increased ionization of the sputtered species Gudmundsson et al.
(2012) JVSTA 30 030801 Gudmundsson (2020) PSST 29 113001 On the connection between the self-sputter yield and deposition rate in HiPIMS operation Overview Thin ﬁlm deposition The ionization region model (IRM) Deposition rate vs ionized ﬂux fraction Working gas rarefaction Summary On the connection between the self-sputter yield and deposition rate in HiPIMS operation Thin ﬁlm deposition On the connection between the self-sputter yield and deposition rate in HiPIMS operation Thin ﬁlm deposition The ﬁlm mass density is always higher when depositing with HiPIMS compared to dcMS at the same average power The surfaces are signiﬁcantly smoother when depositing with HiPIMS compared to dcMS The ﬁlms typically exhibit better crystallinity, and overall improved ﬁlm properties lower electrical resistivity improved optical properties improved mechanical properties better oxidation resistance From Samuelsson et al.
(2010) SCT 202 591 On the connection between the self-sputter yield and deposition rate in HiPIMS operation Thin ﬁlm deposition TiN as diffusion barriers for copper and aluminum interconnects HiPIMS deposited ﬁlms have signiﬁcantly lower resistivity than dcMS deposited ﬁlms on SiO2 at all growth temperatures Thus, ultrathin continuous TiN ﬁlms with superior electrical characteristics and high resistance towards oxidation can be obtained with HiPIMS at reduced temperatures compared to dcMS From Magnus et al.
(2012) IEEE EDL 33 1045 On the connection between the self-sputter yield and deposition rate in HiPIMS operation Thin ﬁlm deposition There is a drawback The deposition rate is lower for HiPIMS when compared to dcMS operated at the same average power The HiPIMS deposition rates are typically in the range of 30 – 85% of the dcMS rates depending on target material Many of the ions of the target material are attracted back to the target surface by the cathode potential From Samuelsson et al.
(2010) SCT 202 591 On the connection between the self-sputter yield and deposition rate in HiPIMS operation The ionization region model (IRM) On the connection between the self-sputter yield and deposition rate in HiPIMS operation Ionization region model The ionization region model (IRM) is a time-dependent volume averaged plasma chemical model of the ionization region (IR) of the HiPIMS discharge The IRM gives the temporal evolution of the densities of ions, neutrals and electrons The IRM gives also two internal parameters that are of importance αt – ionization probability βt – back-attraction probability Detailed model description is given in Huo et al.
(2017) JPD 50 354003 The deﬁnition of the volume covered by the IRM The IR is deﬁned as an annular cylinder of width wrt = rc2 rc1 and − thickness L = z2 − z1, extends from z1 to z2 axially away from the target From Raadu et al.
(2011) PSST 20 065007 On the connection between the self-sputter yield and deposition rate in HiPIMS operation Ionization region model The temporal development is deﬁned by a set of ordinary differential equations giving the ﬁrst time derivatives of the electron energy the particle densities for all the particles (except electrons) The species assumed in the non-reactive-IRM are cold electrons eC, hot electrons eH argon atoms Ar(3s23p6), warm argon atoms in the ground state ArW, hot argon atoms in the ground state ArH, Arm (1s5 and 1s3) (11.6 eV), argon ions Ar+ (15.76 eV), doubly ionized argon ions Ar2+ (27.63 eV) Metal atoms, sometimes metastable states, metal ion M+, and doubly ionized metal ions M2+ Detailed model description is given in Huo et al.
(2017), JPD 50 354003 On the connection between the self-sputter yield and deposition rate in HiPIMS operation Ionization region model As an example the particle balance equation for the metal ion M+ is dnM+ dt = k c iz,MnenM + k h electron impact ionization iz,MnenM + kP,iznArmnM Penning ionization + kchexc,1nMnAr+ + kchexc,2nM2+nAr charge exchange − k c iz,M+nenM+ − electron impact ionization to create M2+ k h iz,M+nenM+ − M+ + ΓBP ΓRT M+(SIR IR V ion ﬂux out of the ionization region SRT) − On the connection between the self-sputter yield and deposition rate in HiPIMS operation Ionization region model The IRM is a semi-empirical discharge model and requires the measured discharge current and voltage waveforms The IRM has three unknown ﬁtting parameters the ion back-attraction probability for the metal ions βt,pulse and gas ions βg,pulse the potential drop across the IR f = VIR/VD the electron recapture probability r = 0.7 This leaves the (βt,pulse, f ) parameter space to be explored through the model ﬁtting procedure – the blue zones in the ﬁtting map indicate the smallest mean square error Graphite target from Eliasson et al.
(2021) PSST 29 115017 On the connection between the self-sputter yield and deposition rate in HiPIMS operation Ionization region model The ionization probability αt increases with increased discharge voltage The peak discharge current increases with increased discharge voltage Earlier we have argued that the ionization probability depends only on the peak discharge current and increases with increased peak discharge current Rudolph et al.
(2022) JPD 55 015202 The back-attraction probability βt,pulse decreases with increased discharge voltage A discharge with tungsten target From Suresh Babu et al.
(2022) PSST 31 065009 5006007008000.50.60.70.80.91 On the connection between the self-sputter yield and deposition rate in HiPIMS operation Ionization region model W: PSST (2022) 31 065009 Cu: SCT (2022) 442 128189 C: PSST (2021) 30 115017 The temporal evolution of the discharge current composition at the target surface for three different targets With Cu target Cu+ ions dominate, with graphite target Ar+ ions dominate 0204060801001200246810121416010203040506070800510152025(a) On the connection between the self-sputter yield and deposition rate in HiPIMS operation Deposition rate vs ionized ﬂux fraction On the connection between the self-sputter yield and deposition rate in HiPIMS operation Deposition rate – αt and βt We can relate the measured quantities normalized deposition rate FDR,sput and the ionized ﬂux fraction Fti,ﬂux FDR,sput = ΓDR Γ0 = (1 αtβt) − Fti,ﬂux = ΓDR,ions ΓDR,sput = Γ0αt(1 Γ0(1 βt) − αtβt) = αt(1 (1 βt) − αtβt) − − to the internal parameters back attraction probability βt βt = 1 − 1 FDR,sput − FDR,sput(1 and ionization probability αt αt = 1 − FDR,sput(1 Fti,ﬂux) Fti,ﬂux) − − Hajihoseini et al.
(2019) Plasma 2 201 and later reﬁned by Rudolph et al.
(2021) JAP 129 033303 On the connection between the self-sputter yield and deposition rate in HiPIMS operation Deposition rate – Optimization There are two measures of how good a HiPIMS discharge is: the fraction FDR,sput of all the sputtered material that reaches the diffusion region (DR) the fraction Fti,ﬂux of ionized species in that ﬂux There is a trade off between the goals of higher FDR,sput and higher Fti,ﬂux The question that remains: How can we vary the ionization probability αt and maybe more importantly the back-attraction probability βt ?
From Brenning et al.

(2020) JVSTA 38 033008 On the connection between the self-sputter yield and deposition rate in HiPIMS operation Deposition rate – Optimization What determines the back-attraction probability ?

How can one inﬂuence the back-attraction probability ?
The back-attraction probability βt,pulse, determined by IRM, versus the self-sputter yield for various target materials The data indicate that the back-attraction probability decreases roughly linearly with increased self-sputter yield Helmersson et al.

(2005) SVC Conf.

Proc.
2005, p. 458 012300.20.40.60.81YSSβt,pulse (a)Cu–Gudmundssonetal.2022C–Eliassonetal.2021Al–Barynovaetal.2023Ti–Rudolphetal.2021W–SureshBabuetal.2022W–SureshBabuetal.2023W–Vavassorietal.2023 On the connection between the self-sputter yield and deposition rate in HiPIMS operation Working gas rarefaction On the connection between the self-sputter yield and deposition rate in HiPIMS operation Working gas rarefaction The sputtered species enter the discharge at considerable energy, which is determined by the cohesive energy of the solid target The interaction between the energetic sputtered particles and the working gas atoms can lead to a reduction in the working gas density – as has been observed experimentally in the HiPIMS discharge The maximum in the degree of working gas rarefaction, determined by the IRM, for various target materials versus the peak discharge current density JD,peak From Barynova et al.
to be submitted 0123020406080100 On the connection between the self-sputter yield and deposition rate in HiPIMS operation Working gas rarefaction HiPIMS discharge with graphite target and JD,peak = 1 A cm−2 Eliasson et al.
(2021) PSST 30 115017 Argon atoms are lost mainly through electron impact ionization by primary and secondary electrons Contributions of kick-out and charge-exchange are negligible Diffusion contributes to a net loss of argon atoms during the pulse, but to a ﬂow into the ionization region after the pulse is off From Barynova et al.
to be submitted On the connection between the self-sputter yield and deposition rate in HiPIMS operation Working gas rarefaction HiPIMS discharge with tungsten target and JD,peak = 0.54 A cm−3 Suresh Babu et al.
(2022) PSST 31 065009 The main contributor to the loss of argon atoms from the IR is kick-out by tungsten atoms sputtered from the target (39 – 48 % contribution) The second most important loss process is electron impact ionization by secondary electrons followed by electron impact ionization by the primary electrons Diffusional reﬁll of argon atoms is the main contributor to adding argon to the IR, while warm and hot argon atoms released from the target to enter the ionization also have a contribution to add argon atoms to the ionization region From Barynova et al.
to be submitted On the connection between the self-sputter yield and deposition rate in HiPIMS operation Working gas rarefaction The relative contributions of the various processes to working gas rarefaction varies greatly depending on the target material ∼ 1 A/cm2 and pg The various contributions versus the atomic mass of the target material for JD,peak Electron impact ionization by primary electrons is rather signiﬁcant for a graphite target, but its role decreases with increased atomic mass 1 Pa ∼ The role of kick-out, or the sputter wind, increases with increased mass of the target atom From Barynova et al.
to be submitted 050100150200020406080100 On the connection between the self-sputter yield and deposition rate in HiPIMS operation Summary On the connection between the self-sputter yield and deposition rate in HiPIMS operation Summary The discharge current composition at the target surface depends on the target material There is an inescapable conﬂict between the goals of higher deposition rate and higher fraction of ionized species in the sputtered material ﬂux The back-attraction probability appears to depend on the self-sputter yield – it is lower for higher self-sputter yield The main contributor to working gas rarefaction for low mass target atoms is electron impact ionization, while for heavy mass target atoms kick-out by the sputtered species is the main contributor On the connection between the self-sputter yield and deposition rate in HiPIMS operation Thank you for your attention tumi@hi.is The slides can be downloaded at http://langmuir.raunvis.hi.is/ tumi/ranns.html ∼ On the connection between the self-sputter yield and deposition rate in HiPIMS operation Further reading J. T. Gudmundsson, Physics and technology of magnetron sputtering discharges, Plasma Sources Science and Technology, 29(11) (2020) 113001 J. T. Gudmundsson, André Anders, and Achim von Keudell, Foundations of physical vapor deposition with plasma assistance, Plasma Sources Science and Technology, 31(8) (2022) 083001 Daniel Lundin, Tiberiu Minea and Jon Tomas Gudmundsson (eds.
), High Power Impulse Magnetron Sputtering: Fundamentals, Technologies, Challenges and Applications, Elsevier, 2020 PlasmaSourcesScienceandTechnologyPlasmaSourcesSci.Technol.29(2020)113001(53pp)https://doi.org/10.1088/1361-6595/abb7bdTopicalReviewPhysicsandtechnologyofmagnetronsputteringdischargesJTGudmundssonScienceInstitute,UniversityofIceland,Dunhaga3,IS-107Reykjavik,IcelandDepartmentofSpaceandPlasmaPhysics,SchoolofElectricalEngineeringandComputerScience,KTHRoyalInstituteofTechnology,SE-10044,Stockholm,SwedenE-mail:tumi@hi.isReceived18April2018,revised20August2020Acceptedforpublication11September2020Published12November2020AbstractMagnetronsputteringdepositionhasbecomethemostwidelyusedtechniquefordepositionofbothmetallicandcompoundthinﬁlmsandisutilizedinnumerousindustrialapplications.Therehasbeenacontinuousdevelopmentofthemagnetronsputteringtechnologytoimprovetargetutilization,increaseionizationofthesputteredspecies,increasedepositionrates,andtominimizeelectricalinstabilitiessuchasarcs,aswellastoreduceoperatingcost.Thedevelopmentfromthedirectcurrent(dc)diodesputtertooltothemagnetronsputteringdischargeisdiscussedaswellasthevariousmagnetronsputteringdischargeconﬁgurations.Themagnetronsputteringdischargeiseitheroperatedasadcorradiofrequencydischarge,oritisdrivenbysomeotherperiodicwaveformsdependingontheapplication.Thisincludesreactivemagnetronsputteringwhichexhibitshysteresisandisoftenoperatedwithanasymmetricbipolarmid-frequencypulsedwaveform.Duetotargetpoisoningthereactivesputterprocessisinherentlyunstableandexhibitsastronglynon-linearresponsetovariationsinoperatingparameters.Ionizedphysicalvapordepositionwasinitiallyachievedbyaddingasecondarydischargebetweenthecathodetargetandthesubstrateandlaterbyapplyinghighpowerpulsestothecathodetarget.Anoverviewisgivenoftheoperatingparameters,thedischargepropertiesandtheplasmaparametersincludingparticledensities,dischargecurrentcomposition,electronandionenergydistributions,depositionrate,andionizedﬂuxfraction.Thedischargemaintenanceisdiscussedincludingtheelectronheatingprocesses,thecreationandroleofsecondaryelectronsandOhmicheating,andthesputterprocesses.Furthermore,theroleandappearanceofinstabilitiesinthedischargeoperationisdiscussed.Keywords:magnetronsputteringdischarge,dcdiodesputtering,sputtering,dcdischarge,reactivesputtering,physicalvapordeposition,E×Bdischarge(Someﬁguresmayappearincolouronlyintheonlinejournal)OriginalcontentfromthisworkmaybeusedunderthetermsoftheCreativeCommonsAttribution4.0licence.Anyfurtherdistributionofthisworkmustmaintainattributiontotheauthor(s)andthetitleofthework,journalcitationandDOI.1.IntroductionPhysicalvapordeposition(PVD)referstotheformationofacondensiblevaporbyphysicalmechanismsandsubsequentdepositionofthismaterialonasubstrateasathinﬁlmorcoating(Mahan2000,Rossnagel2003,Thornton1988).Thiscanbeachievedbyawiderangeofthinﬁlmdeposition0963-0252/20/113001+53$33.001©2020TheAuthor(s).PublishedbyIOPPublishingLtdPrintedintheUKPlasmaSourcesScienceandTechnologyPlasmaSourcesSci.Technol.31(2022)083001(33pp)https://doi.org/10.1088/1361-6595/ac7f53TopicalReviewFoundationsofphysicalvapordepositionwithplasmaassistanceJonTomasGudmundsson1,2,∗,Andr´eAnders3,4andAchimvonKeudell51SpaceandPlasmaPhysics,SchoolofElectricalEngineeringandComputerScience,KTHRoyalInstituteofTechnology,SE-10044Stockholm,Sweden2ScienceInstitute,UniversityofIceland,Dunhaga3,IS-107Reykjavik,Iceland3LeibnizInstituteofSurfaceEngineering(IOM),Permoserstraße15,04318Leipzig,Germany4FelixBlochInstituteofSolidStatePhysics,LeipzigUniversity,Linn´estraße5,04103Leipzig,Germany5InstituteforExperimentalPhysicsII,Ruhr-UniversityBochum,GermanyE-mail:tumi@hi.isReceived29May2021,revised16June2022Acceptedforpublication7July2022Published19September2022AbstractPhysicalvapordeposition(PVD)referstotheremovalofatomsfromasolidoraliquidbyphysicalmeans,followedbydepositionofthoseatomsonanearbysurfacetoformathinfilmorcoating.Variousapproachesandtechniquesareappliedtoreleasetheatomsincludingthermalevaporation,electronbeamevaporation,ion-drivensputtering,laserablation,andcathodicarc-basedemission.Someoftheapproachesarebasedonaplasmadischarge,whileinothercasestheatomscomposingthevaporareionizedeitherduetothereleaseofthefilm-formingspeciesortheyareionizedintentionallyafterward.Here,abriefoverviewofthevariousPVDtechniquesisgiven,whiletheemphasisisonsputtering,whichisdominatedbymagnetronsputtering,themostwidelyusedtechniquefordepositionofbothmetallicandcompoundthinfilms.Theadvantagesanddrawbacksofthevarioustechniquesarediscussedandcompared.Keywords:physicalvapordeposition,magnetronsputtering,cathodicarcdeposition,ionbeamdeposition,sputtering,pulsedlaserdeposition(Somefiguresmayappearincolouronlyintheonlinejournal)1.IntroductionTheformationofacondensiblevaporbyphysicalmechanismsandsubsequentdepositionofthismaterialontoasubstrateasathinfilmorcoatingisreferredtoasphysicalvapordeposition(PVD)(Mahan2000,Rossnagel2003,Thornton1988).Theformationofavaporreferstoaphasetransitionofthefilm-formingmaterialfromasolidorliquidphaseintoagaseousor∗Authortowhomanycorrespondenceshouldbeaddressed.OriginalcontentfromthisworkmaybeusedunderthetermsoftheCreativeCommonsAttribution4.0licence.Anyfurtherdistributionofthisworkmustmaintainattributiontotheauthor(s)andthetitleofthework,journalcitationandDOI.plasmaphase.PVDisabroadfieldandvariousprocessesareappliedtocreatefilm-formingmaterialandtoachievethinfilmdeposition.Physicalvaporcanbecreatedbyawiderangeoftechniques,whichhaveincommonthattheatomsareremovedfromasolidorliquidsourcebyphysicalmeans,momentumexchangeviathermalevaporation,sublimation,ionsputter-ing,electronbeamandlaserablation,and/orarc-basedemis-sion.Historically,vaporwasdescriptiveforthefilm-formingmaterialinevaporationprocesses,asatomsinavaporcanbecharacterizedbytheequilibriumparametertemperature.However,whendescribingmostmodernPVDtechniques,theterm‘vapor’(thegasphaseofasubstanceatatemperaturelowerthanitscriticaltemperature)issomewhatofamisnomer0963-0252/22/083001+33$33.00PrintedintheUK1©2022TheAuthor(s).PublishedbyIOPPublishingLtdHIGH 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