www.DRAFT.ugent.be

Dual magnetron sputtering of mixed oxides

D. Depla

Linköping(SE) 8 and 9 December 2011

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2

Simulation of metal transport: SIMTRA

Experimental set-up

Compositional control

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eExperimental set-up

3

•Unbalanced magnetrons

•Metallic Mg and Al, Cr, Ti, Y and Zr targets

•Id Mg = Cr = 0.5 A

•Id Al = Ti = 0.7 A

•Id Y = Zr = 0.8 A

•P = 0.8 Pa

•Substrate tilted 45°

Film thickness:

1 µm on Si with nativeoxide layer

Mg

M

substra

te

Local O2 inlet

M. Saraiva, H. Chen, W.P. Leroy, S. Mahieu, N. Jenanathan, O. Lebedev, V. Georgieva, R. Persoons, D. Depla,

Plasma Process. Polym. 6 (2009) 751-754

M. Saraiva, V. Georgieva, S. Mahieu, K. Van Aeken, A. Bogaerts, D. Depla, J. Appl. Phys. 107 (2010) 034902

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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Choice for the local oxygen inlet

0.36

0.34

0.32

0.30

Pre

ss

ure

[P

a]

6543210O2 [sccm]

Mg & Al Mg Al

a)

500

450

400

350

300

250

200

150

Dis

ch

arg

e V

olt

ag

e [

V]

6543210O2 [sccm]

Mg (Mg & Al) Al (Mg & Al) Mg Al

b)

Well knownhysteresisbehaviour prevent to deposit fullyoxidized layers at high deposition rate

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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� Substrate� Target � Gas flow

Output of RSD

1.0

0.8

0.6

0.4

0.2

0.0

target condition

543210oxygen flow (sccm)

metal fraction chemisorption compound fraction

1.0

0.8

0.6

0.4

0.2

0.0

substrate con

dition

543210oxygen flow (sccm)

compound fraction

4

3

2

1

0

flow (sccm

)

43210oxygen flow (sccm)

flow to substrate flow to target flow to pump total flow

Just before the critical point, i.e. where the deposition rate is high the substrate is not fully oxidized

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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Typical deposition conditions

20

18

16

14

12

10

8

09121316192125273241

20

18

16

14

12

10

850403020100

7

6

5

4

3

2

4952525254545758605959

20

18

16

14

12

10

8

1008175736558504133220

target position Mg target position Cr oxygen flow

Mg concentration (%)

Cr concentration (%)

O concentration (%)

targ

et-s

am

ple

dis

tanc

e (

cm)

ox

yge

n flo

w (s

ccm

)

Mg metal ratio (%)

com

po

sitio

n

Changing target-substrate distance, and adjusting the oxygenflow allows to deposit fully oxidized thin films with a wide varietyin composition

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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543210

Mg/M

210

543210

210543210

210(dM/dMg)

2

543210

210543210

210

Al Cr Ti Y Zr

A simple approach…

= =

∼

22Mg Mg Mg M

M M Mg2M

AX R d d

CBX R dd

Works quite well, but we can do better…

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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Description : SIMTRA

Mean free path

High energy

Intermediate

Thermal

Initia lisationDescription of the starting position-erosion profile (experimental or simulation)-energy distribution: SRIM or Thompson-nascent distribution: experimental/SRIM/analytical

Does the pathintersect with a

predefined surface?

NoYes

m lnXλ = −λ

m

g

1

nλ =

σs

m

g r

v

n vλ =

σ

m

sg

g

1

mn 1

m

λ =

σ +

M Horkel, K Van Aeken, C Eisenmenger-Sittner, D Depla, S Mahieu, W P Leroy

J. Phys. D: Appl. Phys. 43 (2010) 075302 (7pp)

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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eDescription : SIMTRA

NoDoes the pathintersect with a

predefined surface?

Description a collision

com com 2R 2

2

com

1(E ,p) 2p dr

V(r) pr 1

E r

∞

θ = π −

− −

∫

G o back to the mean free path calculation

Yes

Deposition

A new atom leaves

K. Van Aeken, S. Mahieu, D. Depla

J. Phys. D.:Appl. Phys. 41 (2008) 205307 (6pp)

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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Magnetron 1: Al target

Magne tron 2 : Mg target

Substrate

Composition

Mg/(Mg+Al)

Mg

AlSIMTRA: the result

100

80

60

40

20

0

composition

SIM

TRA

100806040200

composition EPMA

Al Cr Ti Y Zr

Seems simple but is quitecomplicated as one needs a gooddescription of the nascentangular distribution, and the right value for the sputter yield

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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11

Compositional influence

The properties

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Properties

34567

1.52

1.56

1.62

1.65

4.2

3.0

1.8

0.6

0 20 40 60 80 100Mg/(Mg+Al)

H(GPa)

nR a (n

m)

Roughness (optical profilometry)

Refractive index (at 550 nm)

Hardness (nanoindentation)

System : Mg(Al)O

For Mg(Al)O the behaviour is not linear. Origin?

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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eProperties

Mg(Ti)OAC conductivityFour probe measurement

7

6

5

4

3

band

gap (e

V)

100806040200Mg/(Mg+Ti)

Mg(Cr)OOptical transmission(deposition on MgF2)

10-7

10-6

10-5

10-4

AC cond

uctivity (S

m-1)

100806040200Mg/(Mg+Ti)

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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14

A simple model…

Verification with MD simulations

Crystallinity

And the properties…

Crystallinit y : experimental

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eVegard’s law

inte

nsity

(a.u.)

44424038362θ

100% Mg(x0.01)

83% Mg

73% Mg

69% Mg

61% Mg

54% Mg

All Mg(M)O layers behave as a solid so lution. Hence, a clearshift of the MgO peaks is noticed due to substitution of Mg byM, or stated differently the systems follow the empericalVegard’s law.

MgO (111) MgO (200)

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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Vegard’s law: quantitative

-6

-4

-2

0

2

4

6

8

1012x10

-4

slope

-30 -20 -10 0 10 20 30 40radius change(%)

Mg/Al Mg/Cr Mg/Ti Mg/Y Mg/Zr Zr/Y

3.2

3.1

3.0

2.9

2.8

806040200

Al Cr Ti Y Zr

O-O

distanc

e [Å]

M/(Mg+M) (%)

Always good if confirmed…

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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eCrystall inity

0.6

0.4

0.2

706050403020100

0.6

0.4

0.2

706050403020100

0.6

0.4

0.2

7060504030201000.6

0.4

0.2

7060504030201000.6

0.4

0.2

706050403020100M/(M+Mg) %

crystallinity (a

.u.) Mg(Al)O Mg(Cr )O

Mg(Ti)O Mg(Y )O

Mg(Zr)O

Integrating the total intensity of the Mg(M)O (200) pole figureCalibration with MgO powder toovercome defocussing effectTaking into account the film thicknessTaking into account the scatteringfactors

Not yet : density effects

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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Verification with MD simulations…

1818

MgO (0% M)

20%Cr40%Cr 50%Cr 60%Cr

(a)

Cr2O3

Mg(C r)O

V Georgieva, M Saraiva, N Jehanathan, O Lebelev, D Depla and A Bogaerts, J. Phys. D: Appl. Phys. 42 (2009)

065107 (8pp)

MD simulations shows the same transition…

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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eWhat does this learn us?

The structure is ionic. Therefore, as a first approximation, enthalphychanges (driven by Coulomb forces) are probably not so important.

Substitution of Mg by M introduces metal vacancies. Hence, we empty filled octahedral position. So we have a mixture of filled and empty sites. Entropy plays an essential role.

MgOThe structure is a densest packing of O2- anionsThe Mg2+ cations fill the octahedralpositions.

Can we calculate this?

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

Formation enthalphy per MO unitMgO : -601.6 kJ/moleTiO2 : -472.0 kJ/moleAl2O3 : -558.6 kJ/moleY2O3 : -635.1 kJ/moleCr2O3: -379.9 kJ/mole

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A s im ple m odel

Let us put some hard spheres in a box. When their numberincreases, the number of possibilities to arrange themdecreases. Or stated, withincreasing packing density the entropy decreases.But … the densest packing is notrandom but well ordered. Howdoes nature makes it possible toreach this densest packing?

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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eThe hard sphere phase diagram

A first order transition occurs at a packing density between0.494 and 0.545. Here the hard spheres arrange from anamorphous (liquid state) to the crystalline state. Why?The role of the open space between the spheres and the filledspace by the sphere is switched. In the crystalline state the open space is randomly arranged.

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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-25

-20

-15

-10

-5

0

∆S/(N.k)

0.60.40.20.0

packing dens ity

Entropy

∆∆∆∆S, the entropy of the crystal relative to an ideal gas at the same volume and temperature

(1)

(2)

(2) Speedy approximation: ( ) ( ) ( )PV NkT 3 1-z -a z-b z-c=

( )

2 3

3

1+ +PV NkT

1

η η − η=

− η

(1) Carnahan and Starling approximation

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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eMgO structure

MgOThe structure is a densest packing of O2-

anionsThe Mg2+ cations fill the octahedralpositions.

When replacing Mg2+ by M3+ cationsvacancies are formed. Hence, we increasethe open space. However this does notchange the packing density of the O2-

anions.

But we can have a different point of view…

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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First results

0.0

0.50

1.0

crystallinity

0.70.60.50.4packing density

0.0

0.50

1.0

0.70.60.50.4

0.0

0.50

1.0

0.70.60.50.4

0.0

0.50

1.0

0.70.60.50.4

0.0

0.50

1.0

0.70.60.50.4

Cr

Al Y Zr Ti

We can retrieve from the Vegard’s law the correctionneeded for the latticechange

All systems drop aroundthe same packing density, but there is some spread.

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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eFitting and understanding

1.2

1.0

0.8

0.6

0.4

0.2

0.0

crystallinity

0.700.600.500.40

packing density

Al Cr Ti Y Zr

When using the sphere diameter as a fitting parameter (joining all errors) we notice that all systems behavethe same.

Amorphous Crystalline????

b)b)

In the transitionzone, there is equilibrium: amorphous and crystalline regionsshould be noticed

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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Properties: plotted differently

42

0

R (nm)

0.650.600.550.500.450.401.7

1.6

1.5

n

0.650.600.550.500.450.407

53

H(GPa)

0.650.600.550.500.450.40packing density

Roughness (optical profilometry)

Refractive index (at 550 nm)

Hardness (nanoindentation)

System : Mg(Al)O

As a function of the packing density, we notice a (abrupt) change in the behaviour of each studied property.Clearly (nano)crystallinity plays an essential role.

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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eProperties: plotted differently

7

6

5

4

3

band ga

p (eV)

0.600.500.40

10-6

10-5

10-4

σ (

Sm

-1)

0.600.500.40packing density

Mg(Ti)OAC conductivityFour probe measurement

Mg(Cr)OOptical transmission(deposition on MgF2)

A similar conclusion can be drawn for all Mg(M)O systems.

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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28

How to create?

Biaxial alignment: definition

Biaxial alignment of thin films

Single source

Two sources

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eD ef init ion of biax ial aligned thin f ilms

Biaxial alignment: all crystalhave the same out-of-planeand in-plane orientation. A pole figure will show welldefined poles.

Uni-axial alignment: allcrystals have a the same out-of-plane orientation

A pole figure will show a ring.

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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How to deposit a biaxial aligned thin fi lm?

reactive gas N2/O2

Ar

MagnetronMetallic target

α

Tilt the sample ho lder

For dual reactive magnetron sputtering, the sample is inclinedto each target. What is the influence?

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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eComparison: TiN

Pole figureθθθθ/2θθθθ deposition geometry

a

SEM plan view

{200} pole figure

{200} pole figure

500 nm

500 nm

1. 0

0. 8

0. 6

0. 4

0. 2

0. 0

Cps

(a

.u.)

65605550454035302θ (°)

[ 111]

St .St.

1. 0

0. 8

0. 6

0. 4

0. 2

0. 0

Cps

(a

.u.)

65605550454035302θ (°)

[ 111]

St .St.

S. Mahieu, P. Ghekiere, D. Depla, R. De Gryse, Thin Solid Films 515 (2006) 1229-1249

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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Mechanism?

80

60

40

20

0

angle (°)

20151050energy (eV)

160

120

80

40

0

distance (Å)

9075604530150

angle( °)

40

30

20

10

0

distance (Å)

20151050

energy (eV)

Biased diffusion: atomsarriving at the substratekeep their momentum…

X.W. Zhou, H.N.G. Wadley, Surface Science, 431 (1999) 42–57

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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eMechanism?

Atoms move in a given directionover the surface…

The in-plane orientation definesthe efficiency of a grain tocapture atoms.

capture length

9075604530150in-plane orientation γ

Depending on the crystalhabitus one in-plane orientationovergrows the others.

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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Growth conditions?

substrate substrate substrate

thermal energythermal energy

substrate

thermal energy

Zone IIZone TZone Ic

substrate

allowed

intergrain diffusion, competitive overgrowth

Preferential orientation depends on faceting

Zone Ia&b

most tilted facet

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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eSimulations

0. 030. 02

0. 010. 00

9060300

0. 030. 02

0. 01

0. 00

0. 030. 02

0. 01

0. 00

0. 030. 02

0. 01

0. 00

0. 03

0. 020. 01

0. 00

0. 03

0. 020. 01

0. 00

0. 03

0. 02

0. 010. 00

10°

20°

30°

40°

50°

60°

70°

0. 030. 02

0. 010. 00

-90 -60 -30 0 30 60 90

0. 030. 02

0. 01

0. 00

0. 030. 02

0. 01

0. 00

0. 030. 02

0. 01

0. 00

0. 03

0. 020. 01

0. 00

0. 03

0. 020. 01

0. 00

0. 03

0. 02

0. 010. 00

10°

20°

30°

40°

50°

60°

70°

FWHM: 35°

FWHM: 35°

FWHM: 36°

FWHM: 38°

FWH M: 44°

FWHM: 49°

FWHM: 59°

How does the particlearrive at the substrate?

Simulation of Cu at 0.4Pa

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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R esults : a proof for the proposed

m echanism120

100

80

60

40

20

FWHM(°)

70605040302010

tilt angle (°)

MgO YSZ

14

12

10

8

6

4

2

0

inverse diffusion length (a.u.)

70605040302010

tilt angle (°)

0.8

0.7

0.6

0.5

0.4

0.3

0.2

1/diffus

ion leng

th(a.u.)

0.80.60.40.2total pressure (Pa)

24

22

20

18

FWHM (°)

FWHM for YSZ simulation

25

23

21

19

17

15

FWHM (°)

151311975

Target-Substrate distance (cm)

0.20

0.18

0.16

0.14

0.12

0.10

inverse diffusion leng

th (a.u

.)

FWHM YSZ s imulation

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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eAnd dual magnetron sputtering…

Mg

M

substra

te

Local O2 inlet

For dual magnetron sputtering the substrate is inclined to each source.How does this affects the thin film growth?

To study this behaviour let us deposit MgO with twosources, and changing the target substrate distance.

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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MgO/MgO

18.5cm/14.5cm 16.5cm/14.5cm 14.5cm/14.5cm

12.5cm/14.5cm 10.5cm/14.5cm

MgO/MgO

T-S for one sourcechanges, the otheris fixed.

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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eMg(Al)O

Al:18.5cm/Mg:10.5cm Al:16.5cm/Mg:10.5cm Al:14.5cm/Mg:10.5cm

Behaviour is similar, i.e. two sources result in two sets of 3 poles.But: there is a tilt towards the Al source…

Is this general?

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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YSZ

0 15 30 45 60 75 90

15

30

45

60

75

90

0

15

30

45

60

7590

Polar angle (°)

Azimuthal angle (°)

Low pressure

When bringing the Y sourcecloser, the (200) planes tilt towards the Zr target, i.e. in the direction away fromthe Y target which comescloser.

[200] polefigures

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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eMg(M)O

Mg(Al)O Mg(Cr)O Mg(Ti)O Mg(Zr)O Mg(Y)O

The “doping” element defines the tilt.

Inhomogeneousdistribution of M in MgO

Mg MgMM

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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Mg(M)O

-30

-20

-10

0

10

20

30

tilt ang

le (°)

-35 -25 -15 -5 5 15 25 35

cation radius change (%)

MgMgM M

The tilt angle can berelated to the change in the cation radius, i.e. a Vegard’s law effect

-6

-4

-2

0

2

4

6

8

1012x 10

-4

slop

e

-30 -20 - 10 0 10 20 30 40radius change(%)

Mg/Al Mg/Cr Mg/Ti Mg/Y Mg/Zr Zr/Y

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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eConclusions

Ma gne tro n 1: A l targ et

Magn etron 2: Mg ta rget

Su bstrate

Co mpo si ti onMg/ (Mg +A l)

Mg

Al

Composition control is easy by changing currentand T-S distances. This is what we need forexperimental research, but for industrialapplications a one source approach is the obvious choice.

-6-4

-2

0

2

4

6

8

1 012x1 0

-4

slope

-30 - 20 -1 0 0 1 0 20 30 40radius chan ge (%)

Mg /Al Mg /Cr Mg /Ti Mg /Y Mg /Zr Zr/ Y

For the studied mixed oxides the Vegard’s lawbehaviour is observed.

1.2

1.0

0.8

0.6

0.4

0.2

0.0

crysta

llinity

0 .700.600.500.40

p ac king de nsity

Al Cr Ti Y Zr

A surprising simple model helpsto understand the noticedcrystalline-to-amorphoustransition and the connection tothe properties.

4

20

R (nm)

0.650.600.550.500.450.401.7

1.6

1.5

n

0.650.600.550.500.450.407

53

H(GPa)

0.650.600.550.500.450.40pa ck ing dens ity

Due to the chosen deposition conditions and the inclined substrate the film are biaxial aligned.

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

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Acknowledgments

Marta Saraiva: deposition of mixed oxides

IWT: Growth of Complex Oxides : project number 60030

K. Van Aeken : Development of SIMTRA

Flemish Science Foundation

A. BogaertsV. Georgieva

G. VantendelooN. Jehanathan

R. Persoons

M. HorkelC. Eisenmenger-Sittner

Jérika Lamas: deposition of YSZ

Compositional

control

Properties

Crystallinity

Biaxial

alignment

Conclusions

Acknowledgments

ww

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.ug

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t.b

eThank you

Thank you for listening.