HISTORY OF THIN FILMS

Microsoft PowerPoint - as2005_talk_13_Barna.pptHISTORY OF THIN FILMS GROWTH, TECHNIQUES, CHARACTERIZATION
Péter B. Barna Research 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
OUTLINE
HISTORY OF THIN FILMS Number 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 tutorial The main aim of this lecture is to introduce an attempt for synthesizing a view on the structure evolution of elemental and multicomponent polycrystalline thin films, which could be considered as the key issue when thinking about the future of the research and development or even about the diagnosis of technology.
FUTURE
Thin films in 20th century
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Thin films in 20th century: * kind of material peculiar to condensed phase:
structure can be engineered at atomic level new properties
* became a basis of advanced technologies, devices and industries * studied in frame of multidisciplinary research
vacuum science solide state physics and chemistry surface science crystal growth statistical/computational physics adavanced characterization methodes
"Just as rapid advances in vacuum technology were necessary to launch the modern era of thin film technology, it was the phenomenal growth of surface science and applications, together with the continued development and increasing availability of high resolution transmission electron microscopy, that allowed the emerging field of thin films to slowly evolve from a highly advanced empirical art, driven by a very real set of economic and social benefits, 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 tubes erosed 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 substrates 1940th - 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 the elementary processes of structure formation revealed partly by in situ TEM experiments.
OUTCOME Development of * a resource of scientific knowledge on preparation, 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 these THIN FILMS HAVE TAKEN A PROMINENT PART in
* revolutionary development of new active and passive elements,
devices and industries;
TECHNOLOGY PREPARATION METHOD
- material(s) - source - parameters
TECHNOLOGY PREPARATION METHOD
- material(s) - source - parameters
controlled by technology parameters - nucleation - crystal growth - grain growth - restructuring - surface chemical interactions - phase formation, transformation
TECHNOLOGY STRUCTURE EVOLUTION self 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 generally Relationships to be understood for tailoring film
Causality Route of tailoring
Important aspect of technology: evolution of the material structure
The main aspect of thin film technology is that the "self organizing" structure evolution takes place
by an atom-by-atom adding process at temperatures far from thermodynamic equilibrium
which allow the controlled synthesis of
metastable phases artificial structures: multilayers, nanocomposites
Further possibility to control the structure evolution and structure is the co- deposition of minute amount of active additives, an example: aluminium deposition
Cross-section In-plane
Physically separated microcrystals in CoCrTa 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 as inhibitor additive at the deposition of Al films
Grain morphology and texture of Al films deposited at TS = 0,3 Tm
as a function of
the incident Oxygen (Joxygen) to
Aluminium (JAl)) flux ratio P.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 EVOLUTION self organizing process
realized in fundamental phenomena
grain growth bulk diffusion
can be described by the pathway of structure evolution course of the fundamental phenomena
temperature dependence
basis for the evaluation of experimental results
Fundamentals of the self organising nature of thin film growth
concrete structural conditions
determined by the
types of crystal structure
Role of kinetics: diffusion-limited two-dimensional aggregation of atoms
Au deposition on Ag(111) M. Klaua, Proc. 2nd Colloqium on 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 edge diffusion (D1) (A.Barna, P.Thomas, et al., Thin Solid Films, 48, (1978) 163)
Variation of the shape with the edge migration distance (D1) of adatoms:
a) D1 = 0
c) D1 = 4
f) D1 = 8
DISCUSSION IS FOCUSSED on * fundamental phenomena and path-way of structure evolution which 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 by simulation and physical experiments
"Crystal growers have been moving inexorably closer to being able to deposite layers and hence to control film properties on an atom-by-atom basis. We are nearing 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
prepared by
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 (mostly not controlled and known)
material
enviroment
source
substrate
Effect of contamination on the nucleation density and orientation of Au crystals on NaCl cleaved surfaces
carbon contamination of the surface developed during heat treatement of NaCl: affected: nucleation density and orientation M. Krohn, Á. Barna, Proc. 2nd Colloqium on Thin Films, ed: E. Hahn, Akadémiai Kiadó, Budapest, 1967, p.45
clean contaminated
Krohn-Bethge high purity deposition
dependence of Au nucleation density on the level of contamination during deposition M.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
9.5x10-10 1.9x10-9
"In conclusion, we have demonstrated that all aspects of homoepitaxial growth on 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 contamination effects, at first." (P.B. Barna, Proc. 9th International Vacuum Congress, Madrid, 1983, p. 382)
"when reactive surfaces are under study, data from apparently well-characterized samples 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 are likely to be particularly large. When this is the case, it is unclear what inferences to draw 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 representative for 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 the total pressure of active gases in the preparation system ( e.g. water vapour, oxygen, CO, etc.) should be less than 10-10 Pa.
Schematic diagram of a computer-controlled multichamber UHV gas- source molecular-beam epitaxy system (J.E. Greene, MRS Bulletin, 26(2001)777,)
Advanced systems make possible comprehensive investigation of thin film growth processes
Fundamental phenomena and path-way of structure evolution elemental 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 substrate CLUSTERING/NUCLEATION primary
NUCLEATION
ISLAND GROWTH
COALESCENCE 1
COALESCENCE 2
CHANNEL GROWTH
THICKNESS GROWTH
self surface diffusion CRYSTAL GROWTH bulk diffusion COALESCENCE TYPE I complete NUCLEATION secondary
self surfce diffusion CRYSTAL GROWTH bulk diffusion COALESCENCE complete/incomplete GRAIN GROWTH abnormal NUCLEATION secondary
self surface diffusion CRYSTAL GROWTH bulk diffusion GRAIN GROWTH abnormal/normal
The elementary atomic processes and related fundamental phenomena of structure 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 EVOLUTION PHENOMENA
STRUCTURAL PRECONDITIONS active in the next growth stage
SUBSTRATE NUCLEATION
INDIVIDUAL SINGLE CRYSTALS primary- random, secondary- randomCOALESCENCE
complete t y p e I liquid like
secondary nucleation t y p e II
incomplete POLYCRYSTALLINE ISLANDS RESTRUCTURING texture CHANNELS
CRYSTAL GROWTH and GRAIN GROWTH in polcrystalline matrix
CONTINOUS POLYCRYSTALLINE texture
secondary nucleation
AS-GROWN STRUCTURE columnar, polycrystalline uniform grain size - texture in cross section GB-s: perpendicular to the film plane
TS/Tm0,3Zone T Zone II nucleation
crystal growth
DERIVATION of the STRUCTURE ZONE MODEL of elementary thin films growing on amorphous substrate
restructuring growth texturecompetitive growth texturerandom
0,1Zone I adatom migration
on substrate (very limited)
grain growth (abnormal)
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) crystals oo1 oriented crystals of low diffusivity (low potential energy) grow faster than 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 competition takes place among the crystals of various orientation during film growth developing V-shaped columns and changing texture with film thickness (competitive growth texture).
ZONE T structur in TiAlNC coating grown on oxidized Si substrate V-shaped columnar morphology and competitive 111 growth texture
FFT111 texture
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 exist that means: %
conventional structure zone models compiling experimental results are realted to systems contaminated by inhibitor impurity:
Zone III is present Movchan-Demchishin
1969 Thornton
Messier et. al 1984
Grovenor et. al 1984
Fundamental phenomena and path-way of structure evolution two 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 nucleation of A, segregated Bpecies adsorbed adatoms on the growth surface of primary phase A
constituent A: majority component
constituent B: additive composition: A1-xBx, x<0,1
delayed nucleation of secondary phase B on growth surface of primary phase A
B or A1-xsBxs phases are growing in 3D inclusions
B or A1-xsBxs phases are growing in 2D surface covering 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 concentration J. 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-Demchishin 1969
Thornton 1974
The conventional and the derived structure zone models
conventional derived effect of inhibitor additive
3-D INCLUSIONS DEVELOPED IN CO-DEPOSITED FILMS
Al-Pt (2 at%) Al-Ni (5 AT%)
Al6Pt as secondary phase
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 and multicomponent) can be described by a pathway (characteristic for every materials system) on the basis of the same fundamental phenomena of structure formation:
nucleation, crystal growth, grain growth
• The operation of every single fundamental phenomenon is related to a thermally activated 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 species including process induced segregation of excessive pecies resulting in delayed nucleation of secondary phase(s)
FUTURE
• Combination of dedicated physical and simulation experiments at carefully designed conditions with special attention to possible contamination effects
• Dedicated experiments on model material systems for collecting data on the elementary atomic processes (surface and bulk) controlling the cours of the fundamental 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