Thin Film Materials and Coatings Winter Semester 2016/17

Dr. Gunther Richter

Raum 5Q-R11, Tel: 3587

Outline:

1. Basics: Crystallography, Surface Energy, Wulff Shape

2. Vacuum

3. Growth Theories and Models

4. Thin Film Analysis Techniques

5. Physical Vapor Deposition

6. Chemical Vapor Deposition

7. Microstructure Tailoring in Thin film and Nanostructures

Motivation – Thin Film Effect in metallic Films

0,00 0,05 0,10

0,00

0,01

0,02

0,03

0,04

1

23456

7

A

B

C

D

E

F G

a

b

c

de

f

g

Bulge-Testing

Cu/Si Vinci (WC)

Cu/Si Thouless (WC)

Cu/Si Flinn (WC)

Cu/Si Weiss (WC)A Cu/Ag/Si Schmidt (WC)a Cu/Ta/Si Schmidt (WC)

AlxOy/Cu/Si Wiederhirn (WC)

Si3N4/Cu/Si Vinci (WC)

Si3N4/Cu/Si Keller (WC)

SiNx/Cu/Si Shu (WC)

Ti/Cu/Si Xiang (WC)

SiOx/Cu/Si Shen (WC)

1% Al/Cu/Si Weiss (WC)

-Fe/Al2O

3 epi (WC in UHV)

Ag/Si Kobrinsky (WC)

SiOx/Ag/Si Kobrinsky (WC)

Al/Al2O3 epi Dehm (WC)

Al/Si Dehm (WC)

Al/Si Venkatraman (WC)

Al/Si Doerner (WC)

Au/Si Sauter (WC)

Au/W/Si Sauter (WC)

Au/Si Leung (WC)

Si3N4/Au/Si Leung (WC)

Cu/Al2O3 epi Edongue (WC)

Cu/Si Balk (WC)

Cu/Si Keller (WC)

Al/Si Korhonen (X)

Al/Si Paszkiet (X)

SiNx/Al/Si Paszkiet (X)

Au/polyimide single Gruber (X)

Au/polyimide Gruber (X)1 Cu/polyimide Hommel (X)

Cu/Ta/polyimide Gruber (X)

Ta/Cu/Ta/polyimide Gruber (X)

Nix model for Al/Si

von Blanckenhagen model for Al

Nix model for Cu/Si

Nix model for Cu/polyimide

von Blanckenhagen model for Cu

Cu Onuseit (B)

20 nm1000 nm

Wafer curvature

Models

No

rma

lize

d R

T flo

w s

tre

ss

/G

[ ]

1/h [nm-1]

Stress [MPa]

X-Ray

fcc metals

Fe/Al2O

3

Scaling of flow stress with inverse film thickness

Beispiel: Korrelation Mikrostruktur - mechanische Eigenschaften

polycrystalline Cu

10 µm

600nm Cu on (0001) -Al2O3

polycrystalline

epitaxial

-100

0

100

200

300

400

0 100 200 300 400 500

flow

str

ess

[MP

a]

temperature [°C]

epitaxial Cu

50 µm

Mikrostruktureffekt auf die thermischen Fließspannung dünner Cu Schichten

Motivation

• Electronic Materials

• Magnetoelectronics (Tunneling magnetoresistance)

• HT Superconductors

• Thermal Barrier Coatings

2 cm

200 nm

20 Å

ZrO2

Al2O3

Flugzeugturbine

Turbinenschaufel

Gefüge der Wärmedämmschicht

Atomare Struktur

Thin Films: “Examples”

microchip

IBM

micromirrors

Lucent 10 µm 100 µm

Motivation – Thin Film Effect in metallic Films

0,00 0,05 0,10

0,00

0,01

0,02

0,03

0,04

1

23456

7

A

B

C

D

E

F G

a

b

c

de

f

g

Bulge-Testing

Cu/Si Vinci (WC)

Cu/Si Thouless (WC)

Cu/Si Flinn (WC)

Cu/Si Weiss (WC)A Cu/Ag/Si Schmidt (WC)a Cu/Ta/Si Schmidt (WC)

AlxOy/Cu/Si Wiederhirn (WC)

Si3N4/Cu/Si Vinci (WC)

Si3N4/Cu/Si Keller (WC)

SiNx/Cu/Si Shu (WC)

Ti/Cu/Si Xiang (WC)

SiOx/Cu/Si Shen (WC)

1% Al/Cu/Si Weiss (WC)

-Fe/Al2O

3 epi (WC in UHV)

Ag/Si Kobrinsky (WC)

SiOx/Ag/Si Kobrinsky (WC)

Al/Al2O3 epi Dehm (WC)

Al/Si Dehm (WC)

Al/Si Venkatraman (WC)

Al/Si Doerner (WC)

Au/Si Sauter (WC)

Au/W/Si Sauter (WC)

Au/Si Leung (WC)

Si3N4/Au/Si Leung (WC)

Cu/Al2O3 epi Edongue (WC)

Cu/Si Balk (WC)

Cu/Si Keller (WC)

Al/Si Korhonen (X)

Al/Si Paszkiet (X)

SiNx/Al/Si Paszkiet (X)

Au/polyimide single Gruber (X)

Au/polyimide Gruber (X)1 Cu/polyimide Hommel (X)

Cu/Ta/polyimide Gruber (X)

Ta/Cu/Ta/polyimide Gruber (X)

Nix model for Al/Si

von Blanckenhagen model for Al

Nix model for Cu/Si

Nix model for Cu/polyimide

von Blanckenhagen model for Cu

Cu Onuseit (B)

20 nm1000 nm

Wafer curvature

Models

No

rma

lize

d R

T flo

w s

tre

ss

/G

[ ]

1/h [nm-1]

Stress [MPa]

X-Ray

fcc metals

Fe/Al2O

3

Scaling of flow stress with inverse film thickness Scaling of flow stress with inverse film thickness ??

1µm

40°

substrate

Epitaxial, single crystalline multilayers

Tobias Schmidt, Department Arzt

Ag/Ni/Si(100) Multilayers

Influence of microstructure on

mechanical properties:

Polycrystal single crystal

Bulk thin film

FIB

Composite materials

Cornelia Schurr, Department Arzt

Cu/CNT/Cu/Si

Carbon nano tubes display extraordinary properties

Fabrication of composites with defined

microstructure and composition

FIB

2.2 Wachstumsmodi: Inselwachstum

100 nm

35 nm Pt (Inseln) auf (100)SrTiO3: Inselwachstum, Koaleszenz, Keimbildung

TEM Hellfeldaufnahme AFM Aufnahme (Bildgröße 1 mm x 1mm)

Polli (2000)

N. Yun Jin-Phillipp , Department Dosch

Nano particles

polycrystalline

film

epitaxial

layer

R

1/T

Rh/-Al2O3(0001)

• island density: f(TS, R)

• oxidization is function of island facetts

well defined growth conditions required

HRTEM

Island Layer

Max-Planck-Institut für Metallforschung; ZWE Dünnschichtlabor

Pr:Einbau - Au_4f

Arb

itra

ry U

nit

s

100 98 96 94 92 90 88 86 84 82 80

Binding Energy (eV)

DE= 1.0 eV

Mg-k XPS Si 2p

Au 4f7/2 Au 4f5/2

as derived

650°C

700°C

750°C

800°C

Au/SiOx/Si Surfaces

• Au and Si form eutectica (chemical shift)

• evaporation of eutectica at T > 750°C

Nano structuring of surface

Surface reactions

Beri Mbenkum, Department Spatz

Structuring

Beri Mbenkum, Department Spatz

AFM

arteficial nanostructures

• Fabrication process: bottom-up/condensation by PVD

• Crystal morphology: needle / prismatic, diameter 20 -200 nm, Length < 300 µm

1.1 Kristallographie

Das Kristallgitter

7 Kristallsysteme

Aufgrund der Symmetrie von Kristallen gibt es 14

Bravais-Gitter, die zur Beschreibung aller

Kristallstrukturen ausreichen. Die Bravais-Gitter

verteilen sich auf 7 Kristallsysteme. So besteht z.B. das

NaCl Gitters aus 2 kubisch flächenzentrierten

Translationsgittern (eines für Na, eines für Cl), die um

½ ½ ½ gegeneinander verschoben sind.

Gittertypen und Achsensysteme

Bravais-lattice

System Primitivität Benennung Achsen/Winkelbedingunge

n

kubisch 1.) einfach-primitv

2.) zweifach-primitv

3.) vierfach-primitv

eckenbesetzt

raumzentriert

allseitig flächenzentriert

a = b = c, = b = g = 90°

tetragonal 4.) einfach-primitv

5.) zweifach-primitv

eckenbesetzt

raumzentriert a = b c, = b = g = 90°

hexagonal 6.) einfach-primitv

7.) dreifach-primitv

7'.) einfach-primitv

eckenbesetzt

2-fach raumzentriert

rhomboeder-eckenbesetzt

a = b /= c, = 120°, g = 90°

rhombisch

8.) einfach-primitv

9.) zweifach-primitv

10.a) zweifach-primitv

10.b) zweifach-primitv

10.c) zweifach-primitv

11.) vierfach-primitv

eckenbesetzt

raumzentriert

(vorder-) flächenzentriert

(seiten-) flächenzentriert

basiszentriert

allseitig flächenzentriert

a b c, = b = g = 90°

(rhomboedrisch) o. Abb. a = b = c, = b = g 90°

monoklin 12.) einfach-primitv

13.) zweifach-primitv

eckenbesetzt

basiszentriert a b c, = g = 90° b

triklin 14.) einfach-primitv eckenbesetzt a b c, b g 90°

Lattice distances

Angle between planes

Stereographic projection

Wulff Net

Winkel zwischen Kristallebenen

Winkel

Surface crystallography

fünf Bravais-Netze zur Beschreibung der

Oberflächengeometrie mit Einheitsvektoren

as und bs

Translation T = m·as + n · bs

Surface tension/stress/energy

Surface energy

Surface energy

Stereographic Projection/Surface

energy

Wulff Shape

Wulff Shape

Wulff Shape

Max-Planck-Institut für Metallforschung

A.D. Polli SrTiO3

Pt

Wulff plot

gF = r{hkl}

Minimize surface energy with

constant volume

Equilibrium shape

Wulff plot

Growth Theory: simple thermodynamic theory

Free energy change DG

radius r*

SIFFV rararaGraG ggg 2

2

2

2

2

1

3

3 DD

gS: Substrate surface energy ai: geometrical factors

gF: Film surface energy

gIF: Interface energy

layer by layer growth

(Frank van den Merwe, FM)

Film Growth Modes

FIFS ggg FIFS ggg

island growth

(Volmer-Weber, VM)

layer plus island growth

(Stransky-Krasanov, SK)

Complete wetting partial wetting

f

Surf

ace e

nerg

y r

atio

M. Ohring,

Materials Science of

Thin Films, 2002

Layer growth can only tolerate small

amounts of misfit (strain energy)

→ strain relaxation by Stransky-Krastanov Growth

Stability Regions of Growth Modes

Winterbottom

Winterbottom II

Winterbottom III

1

2

r

rFSIF ggg

Winterbottom IV

Gas theory

Vacuum

Vacuum

Vacuum

Charakteristische Größen des Vakuums:

Das Vakuum muss ausreichend sein, damit sich die Probe

während der Messung nicht verändert!

Annahme: Im Vakuum gelten die Gleichungen für das freie Gas:

N: Zahl der Atome

im Volumen V

T: Temperatur

kB: Boltzmann-Konstante

Auftreffrate von Restgasatomen auf der Probe:

m: Masse der Gasatome

Faustregel:

TkV

Np B

mT

pb

Tkm

pr

B

2

12/11224 PaKsm Moleküle1063.2 b12/11226 mbarKsm Moleküle1063.2 b

Freie Weglänge der Restgasmoleküle:

22

p

TkB

Herleitung aus der kinetischen Gastheorie:

: „Durchmesser der Restgasmoleküle

Pumpentyp Druckbereich (Pa)

mech. Drehschieberpumpe Atmosphärendruck - ca. 10-1 Pa

Sorptionspumpe Atmosphärendruck - ca. 10-3 Pa

Öldiffusionspumpe 1 Pa - 10-7 Pa

Turbomolekularpumpe 1 Pa - 10-9 Pa

Kryopumpe 10-1 Pa - 10-9 Pa

Ti-Sublimationspumpe 10 Pa - 10-9 Pa

Ionengetterpumpe 10-3 Pa - 10-9 Pa

Zeit zur Bildung einer Monolage Adsorbat:

Abschätzung: in der Kammer herrscht ein Druck von 1·10-6 mbar

r 3·1014/(cm2s) N2 Moleküle bei Raumtemperatur

1 ML = 1015 Atome/cm2 1 ML adsorbiert alle 3 s

Vakuumerzeugung durch Pumpen:

- Reihenschaltung mehrerer Pumpen

- Pumpwirkung durch Kompression, Diffusion, Gettermaterialien oder Kondensation

- Pumpgeschwindigkeit hängt vom Pumpentyp und dem zu pumpenden Gas ab

Übersicht Vakuumpumpen

Drehschieberpumpe

Diffusionspumpe

Ionengetterpumpe

Turbomolekularpumpe

Übersicht Vakuumpumpen

Vapor pressure

Vapor pressure

Evaporation

Evaporation

Film Thickness

Film Overgrowth

Nucleation barrier

Film nucleation

Film nucleation

Film nucleation

Film nucleation

Film nucleation

Coalescence

Adatom density

Ehrlich-Schwoebel-barrier

Microstructure

Critical cluster size

Film nucleation

Film nucleation

Film nucleation

Defect/trap energy

Nucleation Ag/W(110)

Energy values

Influence of T

Energy values II

Critical nuclei size

Step decoration

Step decoration

Stages of film growth

Coalescence

Nucleation and Growth

22 nm Pt 200 nm Pt

Pt on (100) STO (850°C) (AFM-images) (A.D.Polli)

Images: 10 mm 10 mm

Quantification

(island size distribution, number of islands)

• Number of atoms in a critical nucleus i

• Nucleation energy Ei

• Activation energy for adsorption Ea

• Activation energy for diffusion Ed

• Binding energy Adatom - Defect

Parameters: i, Ei, Ed, Ea

Fundamental processes

e.g. J. A. Venables, Introduction to Surfaces and Thin Films, Cambridge University Press 2000

thickening

Surface preparation: SrTiO3(001)

3 mm

Surface preparation: SrTiO3(001)

2 mm

200 eV, 10 min ion etching Annealing 1 h, 800°C

Pd/SrTiO3(001): STM

Tailoring the microstructure

0.0010 0.0015 0.0020 0.0025 0.0030 0.0035

-5.5

-5.0

-4.5

-4.0

-3.5

-3.0

-2.5 (001) - Körner

(001) + (111) - Körner

(111) - Körner

ln(R

) (ln

(nm

/s))

1/T (K-1)

(001) grains

(001) + (111) grains

(111) grains

- Island growth: temperature independent

- Orientation is function of temperature 30 nm

STM

45 nm Pd <60°C

RHEED

{111}Pd || (001)SrTiO3

50 nm

STM

RHEED

(001)Pd || (001)SrTiO3

[100]Pd || [100]SrTiO3

0,00 0,05 0,10 0,15 0,20 0,25 0,30 0,35

4,0x1015

6,0x1015

8,0x1015

1,0x1016

1,2x1016

1,4x1016

TSub

= 600°C

R = 0.0010 nm/s

R = 0.0049 nm/s

R = 0.0083 nm/s

Isla

nd D

ensity

(m-2)

Film Thickness (nm)

Approximaton of Rate Theory:

ia.u.K.

= 0.85 ± 0.18

iv.K.

= 1.26 ± 0.40

iN i = 1

Ei = 0

p = 0,34 ± 0,07

10-3

10-2

4x1015

6x1015

8x1015

1016

1,2x1016

1,4x1016

log

(nx)

(m-2)

log(Rate) (nm/s)

p(i) = nx (R ) @ TS = constant

Experiment: Rate Dependence

S

Act

0

x

kT

Eexp

D

Rn

pR EAct

p

Ts x

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,810

15

1016

R = 0.0049 nm/s

TS = 500°C

TS = 600°C

TS = 700°C

Isla

nd D

ensity

(m-2)

Film Thickness (nm)

0.00100 0.00105 0.00110 0.00115 0.00120 0.00125 0.00130

35.5

36.0

36.5

37.0

37.5

38.0

EAkt

= (0,63 ± 0,04) eV

ln(n

x)

1/T (K-1)

EAct

= nx(T

S) @ R = constant

S

Act

0

x

kT

Eexp

D

Rn

pR EAct

p

Ts x

Activation Energy Determination

1,00 1,05 1,10 1,15 1,20 1,25 1,30

0,0

5,0x10 -4

1,0x10 -3

1,5x10 -3

2,0x10 -3

2,5x10 -3

Data für R = 0.0049 nm/s 2D-projektion of fit

n x /N

0

1/T (1000/K)

satu

ration isla

nd d

ensity

S

d00x

2/7

0

x

S

a

2/5

0

x1

kT

Eexp

ND

N

n

kT

Eexp

N

nK

Ea = (1.69 ± 0.05) eV ; Ed = (0.64 ± 0.20) eV ; i = 1

Pd/SrTiO3(001): Nucleation

Grain growth and texture

Epitaxial island growth - all island have same crystallographic orientation

- growth of isalnds with minimal interface and surface energy

Polycrystalline layer - Many isalnds with different crystallographic orientation

- Coalescence grain boundaries

- Grain zize is dependand on island nucleation rate I

and island growth rate G

Grain growth and texture

Texture - favoured orientaion between islands/grains relative to the substrate

- Non random orientation

- Fibre texture: d und b constant, random

Grain size

Grain size in polycrystalline thin films:

Simple case:

1. Constant nucleation rate

2. Constant growth rate on surface

Development of Johnson-Mehl structure

d: average grain size

scmI

2

#

s

cmG

3/1

491.1

I

Gd

Reality quite often much more complicated,

but there is a general trend:

Increasing G/I grain size d increases!

Reminder nucleation

How many nuclei form?

(Ohring (1992))

Increase of supersaturation K or

Deposition rate R I increases

Growth velocity?

(z.B. Ohring (1992))

Icrease of substrate temperature T

Growth rate of nucleus G increases

2.4 nucleation and growth

Nucleation and growth (z.B. Ohring (1992))

Increasing G/I grain size d increases

kT

Q*GexpR~

I

G SDn D1

For n > 1 : increasing deposition rate R

Grain size d decreases!

Often seen trend: grain size d increases with

substrate temperature T .

(DG* < QSD)

Exponent n (≈2): dependand on deposition rate

R: deposition rate

DG*: critical nucleation energy (nucleaus with radius r*)

QSD: activation energy for surface diffusion

TEM Hellfeldaufnahme (Querschnitt)

von Pt Inseln auf SrTiO3

Polli (2000)

Grain growth

Normal grain growth Grain boundary migration: lowering total system energy by lowering interface/grain boundary energy

Big grains grow

Small grains shrink

Aberage grain size increases

Growth rate = mobility driving force

driving force: (Energy/Volume)

gbg

r

Grain growth

rm

dt

rdv

gbg

grain growth rate, v

kT

Qmm

gbexp0

Qgb = activation of grain boundary diffusion

r

0r

= average grain boundary energy

= average grain radius

m = average grain boundary mobility

= average starting grain radius

gbg

= curvature

rkT

Q

dt

dr gbgb g

exp~

tkT

Qrr

gb

exp~2

0

2

Grain growth

Driving forece:

Grain boundary energy

Simulation: normal grain growth (Frost (1988))

Stagnation:

Grain boundary grooves

(Mullins (1958)) Microstructure of thin films - average grain size roughly 2 film thickness

r ≈ h (Mullins (1958))

- grain size distribution is log-normal distribution

Frost (1990), Palmer (1987), Gottstein (1999)

Normal grain growth

Grain microstructure in interconnects (Simulation and experiment)

Knowlton (1995)

Normal grain growth in interconnects:

Bamboo structure, gain boundaries „perpendicular“ to interconnect axis

TEM Aufnahme einer Al-Schichten (1% Cu)

Walton (1992)

Abnormal grain growth

Abnormal grain growth: Normal grain growth: stagnation by grain boundary grooves

Additional grain growth abnormal grain growth!

Result: d >> h

Abnormal grain growth

Abnormal grain growth in Ge

(Palmer (1997))

(( h = 30 nm, annealed 1 h @ 900°C)

Growth of (111) grains

Abnormal grain growth in Pd

(Wagner (2001))

( h = 35 nm, annealed 5 min @ 600°C)

Single crystalline (100) thin layer (epitaxial grain growth)

Aufgedampft

und

ausgelagert

Aufgedampft

TEM Hellfeldaufnahme

TEM Hellfeldaufnahme (Querschnitt)

Abnormal Grain Growth

gPd

(111), gPd

(001): A.M. Rodríguez, G. Bozzolo, and J. Ferrante, Surf. Sci. 289 (1993) S.100

SrTiO3

Pd

polykristalline Keime

SrTiO3

Pd

epitaktische Keime

SrTiO3

Pd

polykristalliner Film

SrTiO3

Pd

epitaktischer Film

epitaktische Keime

epitaktische Inseln

Inselwachstum

TSub

=

250°C

<60°C

<60°C

600°C

TSub

=

> 250°C

> 250°C

> 250°C

> 250°C

Glue

Glue epitaxial film epitaxial islands

polycrystalline film

island growth

epitaxial nucleii epitaxial nucleii

polycrystalline nucleii

DF- CTEM

DF- CTEM

gtot(111) = gIF

(111) + gSF(111) > gtot

(001) = gIF(001) + gSF

(001)

gIF(001) = 1.0 Jm-2, gSF

(111) = 1.7 Jm-2, gSF(001) = 2.2 Jm-2

gIF(111) > 1.5 Jm-2

Driving force for abnormal grain growth

Abnormal grain growth

Tfs D

gb

avmin MMW

g

2

gb

i

gb

si/s

hhW

g

gD

g

gD

Strain energy W Surface and interface energy Ws/i

min,iav,ii

min,sav,ss

gggD

gggD

avminfs

is

MMhT

gDgDD

2

2 1

depgg TTT D

W = Ws/i

=> Balance between W - und Ws/i determines texture

Abnormal grain growth

Texture diagram Phasen boundary between (111) and (100) texture

(fcc metals)

Thompson (1995)

DT 2 ~ 1/h

100111

100111

MM

,s,s

gg Result: DT = constant there is a critical thickness hcrit

texture is determined by strain energy

hcrit