Cathodic Arcs: From Fractal Spots to Energetic Condensation

555 Pages·2009·11.27 MB·English

by  André Anders (auth.)

Springer Series on
atomic, optical, and plasma physics 50
Springer Series on
atomic, optical, and plasma physics
TheSpringerSeriesonAtomic,Optical,andPlasmaPhysicscoversinacomprehensive
manner theory and experiment in the entire .eld of atoms and molecules and their
interactionwithelectromagneticradiation.Booksintheseriesprovidearichsourceof
newideasandtechniqueswithwideapplicationsin.eldssuchaschemistry,materials
science,astrophysics,surfacescience,plasmatechnology,advancedoptics,aeronomy,
andengineering.Laserphysicsisaparticularconnectingthemethathasprovidedmuch
ofthecontinuingimpetusfornewdevelopmentsinthefield.Thepurposeoftheseriesis
tocoverthegapbetweenstandardundergraduatetextbooksandtheresearchliterature
withemphasisonthefundamentalideas,methods,techniques,andresultsinthefield.
47 SemiclassicalDynamicsandRelaxation
By:D.S.F.Crothers
48 TheoreticalFemtosecondPhysics
AtomsandMoleculesinStrongLaserFields
ByF.Großmann
49 RelativisticCollisionsofStructuredAtomicParticles
ByA.VoitkivandJ.Ullrich
50 CathodicArcs
FromFractalSpotstoEnergeticCondensation
ByA.Anders
51 ReferenceDataonAtomicPhysicsandAtomicProcess
ByB.M.Smirnov
Vols.20–46oftheformerSpringerSeriesonAtomsandPlasmasarelistedattheendofthebook
Andre´ Anders
Cathodic Arcs
From Fractal Spots to Energetic Condensation
With 262 Figures and 25 Tables
1 3
Andre´ Anders
PlasmaApplicationsGroup
LawrenceBerkeleyNationalLaboratory
Berkeley,CA
USA
[email protected]
ISSN:1615-5653
ISBN:978-0-387-79107-4 e-ISBN:978-0-387-79108-1
DOI:10.1007/978-0-387-79108-1
LibraryofCongressControlNumber:2008929568
#2008SpringerScienceþBusinessMedia,LLC
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InmemoriamIngmarKleberg(1971–2003).
Ingmar wrote an excellent PhD thesis on cathode spot processes, a significant
contributiontothephysicsofarcspotoperationandretrogrademotion.Hewas
a good friend whose time ended abruptly in a tragic accident. He is fondly
rememberedbyhismanyfriends.
Preface
Nottoolongago,afterwatchingDisney’sHerculesmovie,mythen-6-year-old
daughtertestedmebyasking,‘‘Dad,didyouknowthattherearefourelements:
Earth,Water,Air,andLightning?’’Becauseshedidnotusethecommonterms
Earth, Water, Air, and Fire, it struck me that the Greeks may have had an
appreciation for phases: just replace ‘‘element’’ by ‘‘phase,’’ and you will see
theparalleltothemodernterminology:solid,liquid,gas,andplasma!
Althoughtheplasmaphaseisbyfarthemostprevalentintheuniverse(well,
set aside the mysterious dark matter), we have little experience with it in our
daily life. Most plasmas we encounter are man-made, be it the plasma in
fluorescent discharge lamps, plasma displays, or in a welder’s arc. In this
book, a very special case of discharge plasma is explored, the plasma formed
atelectrodes.
Cathodicarcplasmadepositionisoneoftheoldestandatthesametimeone
ofthemodern,emergingdepositiontechnologies.Thisisanapparentlycontra-
dictorystatement.Iwillspanaviewfrommorethanacoupleofcenturiesagoto
recentresearchinthehopetotranspireexcitement,providebackgroundknow-
ledge,andreviewimportantprogress.
Although cathodic arc plasma deposition belongs to the family of physical
vapor deposition (PVD) techniques, I deliberately call it plasma deposition to
emphasize an important feature: energetic condensation of plasma ions, as
opposedtocondensationofatomsfromtheneutralvaporphase.Thesynthesis
of films from ions, each carrying substantial kinetic and potential energy, can
leadtofilmpropertiesthatareunique.
As the name suggests, cathodic arcs are determined by cathode processes.
Indeed,cathodeprocessesarequitedifferentthanprocessesinother,less‘‘vio-
lent’’formsofdischarges.Thecurrentdensitiesandassociatedpowerdensitiesat
cathodespotsareextremelyhigh,andthisistruedespitethecharacteristiclow
cathode fall voltage of typically only 20V. The electron emission processes
involve non-stationary stages and phase transitions, ultimately leading to the
destructionoftheelectronemissioncenter.Thephasetransitionfromthesolid
vii
viii Preface
cathode material to plasma is precisely what enables operation of the arc
discharge and what makes cathodic arc plasmas and the films deposited so
special.
This book is written in the hope to be useful to the experts, practitioners,
students, and newcomers alike. It is assumed that the reader is familiar with
basic concepts of plasma physics and thin films. Thereare manyexcellenttext
booksandreviewarticlesinthefield,andthereforethebasicsaredevelopedhere
onlyastheydirectlyapplytocathodicarcsandthefilmsproduced.Eachchapter
contains an extensive list of references for further reading, and a very brief
introductiontoplasmasandsheathsisgiveninAppendixA.
Writing this book had its challenges. For one, our understanding is still far
fromcomplete,despitetheimpressiveprogressseeninexperimentaltechniques
andtheoreticalmodeling.Yet,itturnedouttobedifficulttodeterminewhatis
really secured knowledge based on accepted, self-consistent data and what are
just hypotheses, even if plausible. The reasons for this difficulty are twofold.
First,arcdatascatterappreciablyduetothenatureofthecathodespotphenom-
ena, and second, some theories contradict each other, even when each is self-
consistentandin‘‘good agreementwithexperimentalobservations,’’asusually
claimed. The underlying problem in modeling is the choice of the simplifying
assumptions,whicharenecessarytomakeduetothecomplexcharacterofthearc
phenomena.Therefore,insomeinstances,Ifailedinmydesiretoproduceatext
bookthatwouldbeacceptabletoallexpertsinthefield.SometimesIneededto
diverttoreviewingwhathasbeendoneandleaveituptothereaderandfurther
researchtoselectthemostappropriatedescriptionofthenatureofcathodicarcs
andthefilmsproduced.AlthoughIbelievethatthereviewportionsarerelatively
extensiveandinclusive,thereiscertainlyworkthathasbeenoverlookedorisnot
sufficientlyappreciated.Iwillnotclaimtohaveproduceda‘‘balancedview.’’
There was the temptation to be as comprehensive and accurate as possible,
whichmayhaveledtoahugebooknobodycouldreadandthatmayhavenever
beenfinished.Perhapsallauthorsrealizeatsomepointthatitisimpossibletodo
a perfect job. Periods of productive work flow were interrupted by times of
distractionandprocrastination.Whywritinganotherarcbook?Therehasbeen
a number of great books, and why could or should I add to this line of work?
Havingaspecialinterestinhistory,Ilookwithadmirationataseriesofbooksby
Joseph Priestley (1767), Vasilii Petrov (1803), Hertha Ayrton (1902), Clement
Child(1913),IgorKesaev(1964,1968),VadimRakhovskii(1970),JamesLafferty
(1980), Gennady Mesyats and Dmitry Proskurovsky (1989), and, last but not
least, the edited Handbook by Raymond Boxman, David Sanders, and Phil
Martin (1995). Each of them represented the state of knowledge and added
substantially to the work of their predecessors. Not to count the numerous
important publications that did not result in a book but became much cited
classicsinthefield.Sincethefieldisvitalandmuchknowledgehasbeenaddedin
recent years, there appeared to be a lack of systematic presentation, and so
I hope toprovidea modern view on thefieldof cathode arcs andthe coatings
madewithcathodicarcplasma.
Preface ix
A book like this one would not be possible without the input by many
colleagues and friends. Here is the perfect opportunity to express my sincere
gratitudefortheirgeneroushelpinfindingthenecessarysupplyofinformation,
diagrams, illustrations, photographic material, raw data, etc. The list of the
many dear colleagues is long, and if I listed them here, some may still be
forgotten. So, I will only mention a few representative names of those who
deservespecialrecognition.IwillstartwithIngmarKleberg,ayoungfriendof
mine whose very untimely death in a mountaineering accident shocked us all.
SomeresultsofhisthesiscanbefoundinChapter3.Idedicatethisbooktohim.
Next,Ishouldstressthatthisworkwasgreatlyinfluencedbythethinkingofmy
formermentors,BurkhardJu¨ttnerandErhardHantzsche,withwhomIspenta
veryproductivetimeinthe1980sinEastBerlinbeforetheBerlinWallfell.From
themIlearnedaboutexplosiveplasmaformationandthespecialroleofcathode
surfaceconditionsthatleadtovariousarcmodesandspottypes.Specialthanks
go to Ian Brown, Berkeley, who introduced me to the world of charge state
analysisandapplicationofarcplasmastothinfilmsandmultilayers.Ianisalso
one of the pioneers of combining arc plasmas and pulsed bias, enabling the
synthesisofveryspecialsurfaces.Hisworkplantedaseedforthetechniqueof
stress control via atomic scale annealing with high-energy ions. Othon Mon-
teiro, former staff scientist of the Plasma Applications Group, contributed
greatly, especially on the issues of energetic condensation and metallization of
semiconductorstructures.MuchofthedataIwasabletocollectcamethrough
thehelpofthetechnicalstaffofthePlasmaApplicationsGroup(thankstoyou,
BobMacGill,MichaelDickinson,JoeWallig,TomMcVeigh)andthevisitorsof
the Plasma Applications Group at Berkeley Lab; many of them have become
distinguished researchers in the field. Just to name a few: Efim Oks (Russia),
Gera Yushkov (Russia), Marcela Bilek (Australia), Jochen Schneider (Ger-
many), Jochen Schein (Germany), Michael Keidar (USA), Johanna Rose´n
(Sweden),SunnieLim(Australia),EungsunByon(Korea),andJoakimAnders-
son(Sweden).
Thelistofhelpfulcolleaguescouldgoonandon,buthereIwillconcludeby
thanking my family for understanding that I was busy so many days and
evenings...Loveyou,Christine,Mark,Mika,andGeorge!
Berkeley,California Andre´Anders
Contents
1 Introduction ............................................ 1
2 ABriefHistoryofCathodicArcCoating...................... 7
2.1 Introduction...................................... 7
2.2 CathodicArcsintheEighteenthCentury ............... 8
2.2.1 TheCapacitor:EnergyStorageforPulsed
Discharges................................ 8
2.2.2 Priestley’sCathodicArcExperiments........... 10
2.2.3 ExperimentsLeadingtotheElectrochemical
Battery................................... 15
2.3 CathodicArcsintheNineteenthCentury ............... 17
2.3.1 ImprovementstotheVoltaicPile .............. 17
2.3.2 Davy’sObservationofPulsed
Discharges................................ 18
2.3.3 Petrov’sObservationofContinuousArc
Discharges................................ 19
2.3.4 Davy’sWorkonContinuousArcDischarges..... 22
2.3.5 ElectromagneticInduction ................... 24
2.3.6 Ru¨hmkorffCoilandPulsedDischarges ......... 24
2.3.7 DischargeExperimentsinGasesand‘‘InVacuo’’.. 26
2.3.8 Faraday’sDeflagrator....................... 28
2.3.9 OpticalEmissionSpectroscopy................ 30
2.3.10 Maxwell.................................. 30
2.3.11 Wright’sExperiments:CoatingsbyPulsed
GloworPulsedArc? ........................ 30
2.3.12 Lecher’sArcExperiments:DiscontinuousCurrent
Transfer.................................. 31
2.3.13 Goldstein’sCanalRays...................... 33
2.3.14 Edison’sCoatingPatents..................... 33
xi
xii Contents
2.3.15 CathodicArcIonVelocityMeasurements ....... 34
2.3.16 EarlyProbeExperimentsinArcPlasmas ........ 35
2.4 CathodicArcsintheTwentiethCentury ................ 36
2.4.1 AroundtheYear1905:Einstein,Weintraub,
Stark,andChild............................ 36
2.4.2 TheDecadesUntilWWII .................... 45
2.4.3 SecretWorkDuringWWII................... 46
2.4.4 TheQuestforthe‘‘Correct’’CurrentDensity
andCathodeModel......................... 47
2.4.5 IonVelocities:ValuesandAcceleration
Mechanism................................ 49
2.4.6 CathodicArcDepositionIsEmerging
asanIndustrialProcess...................... 50
2.4.7 Large-ScaleIndustrialUseinthe1980s
and1990s................................. 55
2.4.8 MacroparticleFiltering:EnablingPrecision
CoatingforHigh-TechApplications............ 56
2.5 CathodicArcsattheBeginningoftheTwenty-First
Century.......................................... 59
2.5.1 AdvancesinDiagnosticsandModelingofArc
PlasmaProcesses........................... 59
2.5.2 ImprovementsofCoatingQualityand
Reproducibility,EnablingHigh-Tech
Applications............................... 60
2.5.3 CathodicArcsforLarge-AreaCoatings......... 61
2.5.4 MultilayersandNanostructuresof
Multi-componentMaterialsSystems............ 62
References............................................. 62
3 ThePhysicsofCathodeProcesses ........................... 75
3.1 Introduction...................................... 76
3.2 TheoryofCollectiveElectronEmissionProcesses:
Steady-StateModels................................ 79
3.2.1 ThermionicEmission........................ 79
3.2.2 Field-EnhancedThermionicEmission .......... 82
3.2.3 FieldEmission............................. 84
3.2.4 Thermo-fieldEmission ...................... 86
3.3 RefinementstotheElectricPropertiesofMetalSurfaces ... 87
3.3.1 JelliumModelandWorkFunction............. 87
3.3.2 TheRoleofAdsorbates...................... 90
3.3.3 TheRoleofSurfaceRoughness ............... 94
3.4 TheoryofCollectiveElectronEmissionProcesses:
Non-stationaryModels ............................. 95
3.4.1 Ion-EnhancedThermo-fieldEmission........... 95
3.4.2 TheExistenceofaCriticalCurrentDensity...... 98