history of thin films - ag...
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HISTORY OF THIN FILMSGROWTH, TECHNIQUES, CHARACTERIZATION
Péter B. BarnaResearch Institute for Technical Physics and Materials Science of HAS
Budapest, Hungary
Autumn School 2005 on Advanced Materials Science and Electron Microscopy
Humbold University of Berlin
Oct. 4th - Oct. 7th, 2005
OUTLINE
HISTORY OF THIN FILMSNumber of publications dealing with thin films is enormously large,impossible to review the investigated problems and results,
but the analysis of the
OUTCOME can be tutorialThe main aim of this lecture is to introduce an attempt for synthesizinga view on the structure evolution of elemental and multicomponent polycrystalline thin films, which could be considered as the key issuewhen thinking about the future of the research and development or evenabout the diagnosis of technology.
FUTURE
Thin films in 20th century
This view is mainly based on the fruitful discussions caried out on this topicduring the last years with Professors J.E. Greene, L. Hultman, I, Petrov and Gy. Radnóczi, as well as with my PhD students Dr. M. Adamik and Dr. A. Kovács.
_____________________________________________________________________
Thin films in 20th century:* kind of material peculiar to condensed phase:
structure can be engineered at atomic levelnew properties
* became a basis of advanced technologies, devices and industries* studied in frame of multidisciplinary research
vacuum sciencesolide state physics and chemistrysurface sciencecrystal growthstatistical/computational physicsadavanced characterization methodes
"Just as rapid advances in vacuum technology were necessary to launch themodern era of thin film technology, it was the phenomenal growth of surfacescience and applications, together with the continued development andincreasing availability of high resolution transmission electron microscopy, that allowed the emerging field of thin films to slowly evolve from a highlyadvanced empirical art, driven by a very real set of economic and socialbenefits, toward an identifiable field of science."(J.E. Greene, J. Vac. Sci. Technol., A 21(2003)S71)
HISTORY End of 19th century - unusual properties of deposits on the walls of glass discharge tubeserosed interest of researchers: optical&electrical properties (P. Drude, Ann. der Physik, 36(1889)532)
1927: - electron diffraction on thin films (Davison - Germer)
1930th- - practical application: high reflectivity surface mirrors on non- conducting substrates1940th - vacuum and thin film (PVD) techniques, devices;
- electron microscopy (Ruska);
1960th- - in situ electron microscopy (Bassett, Pashley, Poppa, Pócza, Honjo) ; - surface decoration (Bassett, Bethge, Distler);- ultrahigh vacuum technique; - surface analytical methodes: Auger spectroscopy, LEED, SEM, ESCA; - structure zone model: compilation of experimental results (Movchan-Demchishin)
1970th - - high resolution (also surface imaging) and analytical TEM ( Halle School); - chemical vapour deposition (CVD); - computer simulation: atom-by-atom structure building (Gilmer&Bennema,
Barna,Thomas et al; Dirks&Leamy)- molecular beam epitaxy (MBE); - CERMET (nanocomposite) resistor films (Neugebauer);
1980th - - atomic resolution surface imaging techniques: STM, AFM (Binning&Röhrer)- atomic layer epitaxy; - electron energy loss analysis - dedicated scanning TEM;
1990th - aberration corrected ultrahigh resolution analytical TEM (Urban);
2000th - advent of in situ techniques (UHV TEM, fast STM, synchrotron)
The pioneering reviews - books
W. Espe and M. Knoll: Werkstoffkunde der Hochvakuumtechnik,(1936)
S. Dushman: Scientific Foundation of Vacuum Techique, (1949)
H. Mayer: Physik dünner Schichten, Teil I (1950) und II (1955)
O. S. Heavens: Optical Properties of Thin Films (1955)
L. Holland: Vacuum Deposition of Thin Films, (1956)
M. Auwärter: Ergebnisse der Hochvakuumtechnik und der Physik dünner Schichten, (1957)
K. L. Chopra: Thin Film Phenomena, (1969)
L. I. Maissel, R. Glang: Handbook of Thin Film Technology, (1970)
H. Mayer: Physics of thin films Parts, I and II, (Complete bibliography), (1972)
B. Lewis, J.C. Anderson: Nucleation and Growth of Thin Films (1978)
Remark: the book of B. Lewis, J.C. Anderson is a comprehensive rewiev of the results on theelementary processes of structure formation revealed partly by in situ TEM experiments.
OUTCOMEDevelopment of* a resource of scientific knowledge onpreparation, structure evolution and structure - property causality of thin films
* advanced and sophisticated thin film preparation devices
and methods based on advances in vacuum technology
* advanced characterization devices and methods
as a consequence of theseTHIN FILMS HAVE TAKEN A PROMINENT PART in
* revolutionary development of new active and passive elements,
devices and industries;
* metamorphosis of society to "information society"
TOPICS OF INVESTIGATIONS AND THE CAUSALITY
TECHNOLOGYPREPARATION METHOD
- material(s)- source- parameters
TECHNOLOGYPREPARATION METHOD
- material(s)- source- parameters
APPLICATIONAPPLICATION
PHYSICAL and CHEMICAL PROPERTIES
PHYSICAL and CHEMICAL PROPERTIES
TECHNOLOGYSTRUCTURE EVOLUTIONself organizing process
controlled by technology parameters- nucleation- crystal growth- grain growth - restructuring- surface chemical interactions- phase formation, transformation
TECHNOLOGYSTRUCTURE EVOLUTIONself organizing process
controlled by technology parameters- nucleation- crystal growth- grain growth - restructuring- surface chemical interactions- phase formation, transformation
STRUCTURE• phase state• morphology of grains and
surfaces• structure of crystals• orientation of crystals, texture• chemical composition• homogeneity• substrate - film interface
STRUCTURE• phase state• morphology of grains and
surfaces• structure of crystals• orientation of crystals, texture• chemical composition• homogeneity• substrate - film interface
Relationships investigated generallyRelationships to be understoodfor tailoring film
CausalityRoute of tailoring
Important aspect of technology: evolution of the material structure
The main aspect of thin film technology is that the "selforganizing" structure evolution takes place
by an atom-by-atom adding processat temperatures far from thermodynamic equilibrium
which allow the controlled synthesis of
metastable phasesartificial structures: multilayers, nanocomposites
Further possibility to control the structure evolution and structure is the co-deposition of minute amount of active additives, an example: aluminiumdeposition
Cross-section In-plane
Physically separated microcrystals inCoCrTa recording media (Sinclair, 1992)
FePt recording media doped with SiO2 (Sáfrán et.al. Thin Solid Films, in print)
cross section
Tailoring of nanocomposite structures by codepiting inhibitor additive
Operation of oxygen asinhibitor additive at thedeposition of Al films
Grain morphology and texture of Al films depositedat TS = 0,3 Tm
as a function of
Koxygen = Joxygen/JAl
the incident Oxygen (Joxygen) to
Aluminium (JAl)) flux ratioP.B. Barna, M. Adamik, Thin Solid Films, 317(1998)27
P.B. Barna, M. Adamik, Thin Solid Films, 317(1998)27; I. Petrov, P.B. Barna, L. Hultman, J.E. Greene, J. Vac. Sci. Technol.,21(2003)S117)
STRUCTURE EVOLUTIONself organizing process
realized infundamental phenomena
nucleationadatom migration
crystal growthadatom self surface diffusion
grain growthbulk diffusion
can be described by thepathway of structure evolutioncourse of the fundamental phenomena
temperature dependence
derivedstructure zone models
related to thermally activatedatomic processes
basis for the evaluationof experimental results
Fundamentals of the self organising nature of thin film growth
concretestructuralconditions
at any instantstructural
preconditions
STRUCTURE EVOLUTIONself organizing process
determined by the
controlled by
TECHNOLOGYPARAMETERS
- electronic structure ofconstituent atoms
types of crystal structure
- thermodynamics- kinetics
phase statematerial structure
Role of kinetics: diffusion-limited two-dimensional aggregation of atoms
Au deposition on Ag(111) M. Klaua, Proc. 2nd Colloqiumon Thin Films, ed. E. Hahn, Budapest, 1967, p. 152.
a-Ge islands grown on cleaved NaCl (100) surface. Computer simulation of growth on a square lattice considering limited edgediffusion (D1) (A.Barna, P.Thomas, et al., Thin Solid Films, 48, (1978) 163)
Variation ofthe shapewith the edgemigrationdistance (D1) of adatoms:
a) D1 = 0
c) D1 = 4
f) D1 = 8
DISCUSSION IS FOCUSSED on* fundamental phenomena and path-way of structureevolutionwhich can make possible
- to understand* the formation mechanisms of various structures* operation of additives/contaminants* interpretation of experimental results
- tailoring designed structures to achieve the specified properties- selection and tailoring the adequate preparation method and
parameters- diagnosis of thechnolgy
* aspects and problems of the preparation of thin film structures bysimulation and physical experiments
"Crystal growers have been moving inexorably closer to being able to depositelayers and hence to control film properties on an atom-by-atom basis. We arenearing an era in which it will be possible to deposite"designer" materials with a specified set of properties." (J.E. Greene, MRS Bulletin, 26(2001)777)
mono crystal polycrystal amorphous
elementalmono phase
prepared by
MC/MD simulationphysical experiments
multicomponentmono or poly phase
prepared by
(MC/MD simulation) physical experiments
contamination contamination
deviation fromstoichiometry
Types of thin films and preparation modes
Aspects and problems of the preparation of thin film structures by simulation and physical experiments
Preparation by simulation experiments:Kinetic Monte Carlo (MC) and molecular dynamic (MD)
- related to idealized systems: species, building the structure, are known- present direct insight into the behaviour of adatoms and atomic interactions
- but: high amount of data of activation barriers are required
- crucial is the knowledge of the correct potentials
Preparation by physical experiments:conditions are far from idealized system: contamination- substrate contamination ( bulk, adsorbed gases)
- deposition takes place in an environment:
co-depositing environmental impurity species (mostlynot controlled and known)
material
enviroment
source
substrate
Effect of contamination on the nucleation density and orientation ofAu crystals on NaCl cleaved surfaces
carbon contamination of the surfacedeveloped during heat treatement ofNaCl: affected: nucleation density andorientationM. Krohn, Á. Barna, Proc. 2nd Colloqium on Thin Films, ed: E. Hahn, Akadémiai Kiadó, Budapest, 1967, p.45
clean contaminated
[111] [001] + random
Krohn-Bethgehigh puritydeposition
dependence of Au nucleation density on thelevel of contamination during depositionM.Kroh, H.Bethge, Thin Solid Films, 57(1979)227
Effect of additives on the monolayer growth: epitaxial Pt film(Poelsema et al.: Acta Phys. A, 53(1991)369)
Kox~10-3 Kox~10-2 Kox>10-1 Kox~ 10-3
Effect of oxygen on the surface growth morphology of Al films (TS = 3000 C) (Barna et al.: phys. stat. sol. a., 55, (1979) 427 )
truncation by step bunching
Effect of CO adsorption on the growth of Pt on Pt(111) surface at 400 K (M. Kalff, G. Comsa, Th. Michely, PRL 81(1998)1255) (STM topograhs, scan size 1700 X 2500 Å.)
< 5x10-12
"clean"1x10-10 4.7x10-10
Parcial pressure of CO during deposition, mbar
9.5x10-10 1.9x10-9
"In conclusion, we have demonstrated that all aspects of homoepitaxial growthon Pt(111) are influenced by minute amounts of adsorbed CO."
Conclusions on impurity effects" Experiencing the development of unusual structural features one has to search for contaminationeffects, at first." (P.B. Barna, Proc. 9th International Vacuum Congress, Madrid, 1983, p. 382)
"when reactive surfaces are under study, data from apparently well-characterizedsamples may be governed by contaminant effects. The reason is that gas species from the ambient tend to adsorb at defects, such as island edges, where their effects arelikely to be particularly large. When this is the case, it is unclear what inferences todraw from agreement of simulations with experiment." (P. J. Feibelman, PR B 60(1999)4972.
"The experiments presented indicate also that in order to obtain results representativefor a clean growth system, impurity atom to deposit atom impingement rates(Kimp/dep = Nimp/Ndep) of 10-4 or below may be necessary. This is substantially less than previously anticipated." (M. Kalff, G. Comsa, Th. Michely, PRL 81(1998)1255)
That means: for clean system at 1 monolayer/s deposition rate thetotal pressure of active gases in the preparation system ( e.g. watervapour, oxygen, CO, etc.) should be less than 10-10 Pa.
Schematic diagram of a computer-controlledmultichamber UHV gas-source molecular-beamepitaxy system(J.E. Greene, MRS Bulletin, 26(2001)777,)
Advanced systems makepossible comprehensiveinvestigation of thin film growth processes
Fundamental phenomena and path-way of structure evolutionelemental system: growth of high purity indium film at Ts = 0,6 Tm, (UHV in situ TEM experiment, J.F.Pócza, Proc. 2nd Coll. on Thin Films, Budapest, 1967)
migration of adatoms on substrateCLUSTERING/NUCLEATION primary
NUCLEATION
GROWTH STAGES
atomic processesFUNDAMENTAL PHENOMENA
self surface diffusionCRYSTAL GROWTH on substrateNUCLEATION primary
ISLAND GROWTH
COALESCENCE 1
COALESCENCE 2
CHANNEL GROWTH
THICKNESS GROWTH
self surface diffusionCRYSTAL GROWTHbulk diffusionCOALESCENCE TYPE I completeNUCLEATION secondary
self surfce diffusionCRYSTAL GROWTH bulk diffusionCOALESCENCE complete/incompleteGRAIN GROWTH abnormalNUCLEATION secondary
self surface diffusionCRYSTAL GROWTHbulk diffusionGRAIN GROWTH abnormal/normal
The elementary atomic processes and related fundamental phenomena ofstructure formation operating in various stages of film growth (elemental film, TS> 0,3Tm)
(P.Barna, in Diagnostics and Application of thin films, Ed. L. Eckertova, I. Ruzicka, IOP, 1992, p.295)
PATH-WAY of STRUCTURE EVOLUTION of ELEMENTAL FILMS in range TS ≥ 0,3 Tm(P.Barna, in Diagnostics and Application of thin films, Ed. L. Eckertova, I. Ruzicka, IOP, 1992, p.295)
STAGES of STRUCTURE EVOLUTIONPHENOMENA
STRUCTURAL PRECONDITIONSactive in the next growth stage
SUBSTRATENUCLEATION
CLUSTERS – NUCLEI random, randomCRYSTAL GROWTH on substrate
INDIVIDUAL SINGLE CRYSTALSprimary- random, secondary- randomCOALESCENCE
completet y p e I liquid like
secondary nucleationt y p e II
incompletePOLYCRYSTALLINE ISLANDSRESTRUCTURING textureCHANNELS
CRYSTAL GROWTH andGRAIN GROWTH in polcrystalline matrix
CONTINOUS POLYCRYSTALLINEtexture
INDIVIDUAL SINGLE CRYSTALSrandom texturerandom texture
secondary nucleation
FILLING THE CHANNELSCRYSTAL and GRAIN GROWTH
AS-GROWN STRUCTUREcolumnar, polycrystallineuniform grain size - texture in cross sectionGB-s: perpendicular to the film plane
TS/Tm0,3Zone T Zone IInucleation
crystal growth
DERIVATION of the STRUCTURE ZONE MODEL of elementary thin filmsgrowing on amorphous substrate
restructuring growth texturecompetitive growth texturerandom
0,1Zone Iadatom migration
on substrate(very limited)
self.surf.diff.(very limited)
nucleation(crystal growth)
adatom migrationon substrate
adatom migrationon substrate
nucleationcrystal growth (competitive)
self.surf.diff. self. surf. diffbulk diffusionGB migration
grain growth (abnormal)
thic
knes
s
TS/Tm0,3Zone T Zone IInucleation
crystal growth
STRUCTURE EVOLUTION IN ZONE T: COMPETITIVE GROWTH OF Aluminium CRYSTALS ON AMORPHOUS SUBSTRATES at TS= 100K
(Simulation experiment: F.H.Bauman, D.L.Chopp, T.Diaz de la Rubia, G.H.Gilmer, J.Greene, H.Huang, S.Kodanbaka, P. O’Sullivan, I.Petrov, MRS Bulletin, 26 (2001) 182)
(111) crystals, (100) crystalsoo1 oriented crystals of low diffusivity (low potential energy) grow fasterthan 111 oriented ones of high surface diffusivity (high potential energy)
Characteristic for Zone T: coalescence (grain growth) does not operate
On amorphous substrates nuclei are randomly oriented, growth competitiontakes place among the crystals of various orientation during film growthdeveloping V-shaped columns and changing texture with film thickness(competitive growth texture).
ZONE T structur in TiAlNC coating grown on oxidized Si substrateV-shaped columnar morphology and competitive 111 growth texture
FFT111 texture
flat - smooth surface
restructuring growth texturecompetitive growth texturerandom
Conclusions on structure evolution in elemental thin films* correlation exists between grain size, grain morphology, surface
topography and texture, these are developing together* the in-plane size (column diameter) and the orientation of crystals
can be controlled by the temperature* the as-deposited structure has low thermal stability* the possible zones are: Zone I, Zone T and Zone II* in Zones I and II the structure and orientation are uniform along
thickness, crystals penetrate through the film * no grain boundaries parallel to the substrate, i.e. no equiaxed grain
morphology (Zone III ) can existthat means: %
conventional structure zone models compiling experimental resultsare realted to systems contaminated by inhibitor impurity:
Zone III is presentMovchan-Demchishin
1969Thornton
1974
Messier et. al1984
Grovenor et. al1984
Fundamental phenomena and path-way of structure evolutiontwo component system: growth of carbon doped indium film, Ts = 0,6 Tm, (in situ TEM experiment, Pócza et al., Jpn. J. Appl. Phys., Suppl. 2, Part 1.(1974)525)
Nucleation and competitive growth of constituent's phases composition: A1-xBx, x<0,1 : limited mutual solubility, no reaction phase of A1-xsBxs
primary nucleationof A, segregatedBpecies adsorbedadatoms on thegrowth surface ofprimary phase A
constituent A: majoritycomponent
constituent B: additivecomposition: A1-xBx, x<0,1
delayednucleation ofsecondaryphase B ongrowth surface ofprimary phase A
B or A1-xsBxs phases are growing in 3D inclusions
B or A1-xsBxs phases are growing in 2D surfacecovering layer : tissu phase, inhibitor additive,
Tailoring of TiN structure by codepositing Si
3 nm
Modfel of TiSiN nanocomposite structure, S. Veprek, Thin Solid Films 297(1997)145
Changes of TiN structure with increasing Si concentrationJ. Patscheider, Th. Zehnder, M. Diserens, Surf. Coat. Technol., 146-147(2001)201
STRUCTURE ZONE MODEL of oxygen doped aluminium film(P.B. Barna, M. Adamik, in Protective coatings and thin films, (Eds. Y. Paulea, P.B.Barna, Kluver 1997, p.279)
Movchan-Demchishin1969
Thornton1974
Messier et. al1984
Grovenor et. al1984 Barna-Adamik, 1988
The conventional and the derived structure zone models
conventional derivedeffect of inhibitor additive
3-D INCLUSIONS DEVELOPED IN CO-DEPOSITED FILMS
Al-Pt (2 at%) Al-Ni (5 AT%)
Al6Pt as secondary phase
A.Kovács et al., Proc. ICEM15, Durban SA, 2002, p.687
P.B.Barna, in L.Eckertova, T Ruzicka, Diagnostics and Applications of Thin Films, IOP 1992, p.295
Conclusions(P.B. Barna, M. Adamik, Thin Solid Films, 317(1998)27; I. Petrov, P.B. Barna, L. Hultman, J.E. Greene, J. Vac. Sci. Technol.,21(2003)S117)
• The structure evolution in polycrystalline films (both elemental andmulticomponent) can be described by a pathway (characteristic for everymaterials system) on the basis of the same fundamental phenomena ofstructure formation:
nucleation, crystal growth, grain growth
• The operation of every single fundamental phenomenon is related to a thermallyactivated atomic process (temperature dependence of the pathway)
• The atomic processes are: adatom diffusion (Ts > ~ 0,05Tm) (nucleation)self surface diffusion (Ts > ~ 0,1Tm) (crystal growth, coalescence)bulk diffusion (Ts > ~ 0,3Tm) (grain growth)
in multicomponent films additionally:chemical interaction among speciesincludingprocess induced segregation of excessive peciesresulting indelayed nucleation of secondary phase(s)
FUTURE
• Combination of dedicated physical and simulation experiments at carefullydesigned conditions with special attention to possible contamination effects
• Dedicated experiments on model material systems for collecting data on theelementary atomic processes (surface and bulk) controlling the cours of thefundamental phenomena of structure formation
• Comprehensive causality analysis of preparation-structure-properties
• Comprehensive structure analysis (bulk and surface) at atomic resolution
• Extended application of in situ and combinatorial experimental methods