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