texture development during thin film magnetron sputter...

1

Texture Development during Thin Film Magnetron Sputter Deposition

Diederik Depla, Sigelinde Van Steenberge

Design, Research And Feasibility of Thin FilmsGhent University

Diederik Depla MRS Spring meeting 2015 www.DRAFT.ugent.be

Some history

Structure zone models

Quantification

1

Some history AZO CeO2 HEA Inclined surfaces Conclusions

2


SZM : main focus on microstructure

Thornton, J.A.,Influence of apparatus geometry and depositionconditions on structure and topography of thicksputtered coatings. Journal of vacuum science &technology, 1974. 11(4): p. 666-670

Movchan, B.A. and A.V. Demchishin,Investigation of the structure and properties of thickvacuum- deposited films of nickel, titanium,tungsten, alumina and zirconium dioxide. FizikaMetallov i Metallovedenie, 1969. 28(4): p. 653-60

Grovenor, C.R.M., H.T.G. Hentzell, and D.A. Smith,The development of grain-structure during growthof metallic-films. Acta metallurgica, 1984. 32(5): p.773-781

Different zones for evaporated metal thin films. Main conclusion : dependence on the ratio of the substrate-to-melting temperature T/Tm

Further optimized by Sanders et al. Sanders, J.V., Chemisorption and Reaction onMetallic Films. Vol. 1. 1971, London: Academic PressInc. LTD.

Grain growth during thin film deposition depends on T/Tm

Influence of the deposition conditions, i.e. pressure on the microstructure.New zone.

But … what about quantification and texture ?2



Quantification

Characteristic diffusion length is defined as the typical length adatoms can diffuse before they are capture by existing islands or form a new nucleus

1 6D

LF

Defined by the ratio between the diffusion rate and the flux

For metals the diffusion processes are well defined*.

Process D0 (cm2.s) C

Mass surface diffusion 5x10-4 6

Mass bulk diffusion 0.3 17

Adatom surface hopping 2x10-4 1.5

Vacancy bulk diffusion 0.05 7

Interstitial bulk diffusion 1x10-4 1.5

s,A A

m o,A o,B B m s,B

T CT ln D D C T / T

Surface diffusion starts at T/Tm = 0.1Grain boundary diffusion at 0.3.With the numbers from the table we can quantify the SZM.

12

10

8

6

4

2

0

ln (

grai

nsi

ze (

Å)

)

20151050

Tm/Ts

Al Ni Au Pb Co Pt Cr Ti Cu W

characteristic length L

*Flynn, C.P., Point defect reactions at surfaces and in bulk metals. Physical Review B, 2005. 71(8).085422

m sCT /ToD D e

3


3


Quantification

substrate

substrate

substrate

8x10-8

7

6

5

4

3

2

1

0

L (a

.u.)

181512963N2 flow (sccm)

zone Ic

zone T

zone II

random/zone Ic [111]/zone T [200]/zone T [111]+[200]/zone II [200]/zone II

The energy flux normalisedper arriving atom is the EPA.

1 6D

LF

Measure the energy flux (calorimetric or active probe)

Measure the deposition rate

Mahieu, S. and D. Depla,Reactive sputter deposition of TiN layers:modelling the growth by characterization ofparticle fluxes towards the substrate. Journal ofPhysics D-Applied Physics, 2009. 42(5).053002

a To

kED D e a fraction AEo

EPD D e

4



And texture…

No preferential texture

Preferential orientationdefined by the fastest out-of-plane growth

CrystallinePreferential orientationdefined by the lowest surface energy.

1 6D

LF

Mahieu, S., P. Ghekiere, D. Depla, and R. De Gryse, Biaxial alignment in sputter deposited thin films.Thin Solid Films, 2006. 515(4): p. 1229-1249

Conflict ?

5

4

3

2

1

0

hal

f of t

he

surf

ace

bin

din

g en

ergy

(eV

)

40003000200010000

melting temperature (K)

slope = 0.0012101 K/eV

SBE depends on Tm

5


4


Case study 1 : Deposition of AZO/Hydroxyapatite

Deposition conditions for AZO

EPA

Similarity with hydroxyapatite

6



AZO depositionCircular planar magnetron2 inch diameter cathode

Rotating cylindrical magnetronTube dimensions : 18 cm x 4 cmSupplier : Soleras Advanced CoatingsComposition : AZO (Al 2wt%)

Supplier : K. LeskerComposition : AZO (Al 2 wt%)

Interesting to know :

The negative oxygen ion angular distribution differs strongly between both targets*

*De Gryse, R., J. Haemers, W.P. Leroy, and D. Depla,Thirty years of rotatable magnetrons. Thin Solid Films, 2012. 520(18): p. 5833-5845

140

120

100

80

60

40

20

0

ene

rgy

flux

(mW

/cm

2 )

76543target substrate distance (cm)

Planar AZO Rotatable AZO

1.0

0.8

0.6

0.4

0.2

0.0

dep

ositi

on r

ate

(nm

/s)

12108642target-substrate distance (cm)

Planar AZO target Rotatable AZO target (0.22 A) Rotatable AZO target (0.17 A)

Energy flux is strongly differentDeposition rate comparable

7


5


Experimental values are consistentwith results published by differentresearch groups

Ellmer, K. and R. Mientus, Carrier transport in polycrystalline transparent conductive oxides: A comparative study of zinc oxide and indium oxide.Thin Solid Films, 2008. 516(14): p. 4620-4627

Parameter spaceTemperature Target substratePressureComposition

8



Texture and properties

104

2

4

6

810

5

2

4

6

810

6

2

4

6

810

7

(002

) pe

ak a

rea

norm

alis

ed fo

r th

ickn

ess

3.02.82.62.42.22.0

diffusion length (a.u.)

1

2

3

4

5

678

10

2

3

4

5

678

resistivity (.cm

)

During the initial phase we expect random nucleation. Anevolutionary overgrowth mechanism explains the (002)preferential orientation for thicker films.

Connection to electrical properties : (002) : wellaligned crystals in plane Other directions : grainsare non well aligned

Li, W.J., E.W. Shi, W.Z. Zhong, and Z.W. YinGrowth mechanism and growth habit of oxide crystals. Journal of Crystal Growth, 1999. 203(1-2): p. 186-196

9


6


Similarity with hydroxyapatite

Ivanova, A.A., M.A. Surmeneva, R.A. Surmenev, and D. Depla,Influence of deposition conditions on the composition, texture and microstructure of RF-magnetron sputter-deposited hydroxyapatite thin films. Accepted for publication in Thin Solid Films,

RF deposition of hydroxy-apatite on a moving substrate holder.Deposition conditions : 0.4 Pa (90% Ar, 10% H2O), T-S 40 mm

10

8

6

4

2

0

time

in r

acet

rack

pe

r pe

riod

(s)

100806040200

position on substrate holder (mm)

10



Case study 2 : Deposition of CeO2

Deposition conditions

EPA

Target condition and ion bombardment

11


7



pbase < 2 x 10-4 PaS ≈ 100 L/spAr = 0.5 PaIdischarge = 0.25 A

metallic mode poisoned mode

metallic mode

poisoned mode

Van Steenberge, S., W.P. Leroy, and D. Depla, Influence of oxygen flow and film thickness on the texture and microstructure of sputtered ceria thin films. Thin Solid Films, 2014. 553: p. 2-6

12



Energy per arriving atom : EPA

Strong drop in deposition rate, relativeconstant energy flux

That is not what I see …

14

12

10

8

6

mea

n th

erm

al p

ower

/are

a (m

W/c

m²)

5.04.03.02.01.0

O2 flow (sccm)

140

120

100

80

60

40

20

0 Fp

, av

(1013

pa

rtic

les/

(cm

² *

s))

3000

2500

2000

1500

1000

500

0

EP

A (

eV

/ad

ato

m)

5.04.03.02.01.0

O2 flow (sccm)

As the energy per arriving particle (EPA) increases strongly a zone transition is expected.

13


8


Target condition1.0

0.8

0.6

0.4

0.2

0.0

pref

eren

tial c

ryst

allin

e or

ient

atio

n

2.52.01.51.00.50.0

racetrack depth (mm)

[111] [200] [220]

The preferred orientation changes a function of the erosion depth of the target.

The target was first sputter cleanedin pure Ar (pressure 0.5 Pa,discharge current 0.25 A, andpumping speed 108 L/s). 3 sccm ofO2 was added to fully poison thetarget.

Film thickness 200 nm

14



Measurement set-up

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

eros

ion

dep

th (

mm

)

25 20 15 10 5 0

distance from the target center (mm)

position energy flux monitor

position MS/sample

100

80

60

40

20

0

norm

alis

ed O

- inte

nsity

3020100

tilt angle (°)

Clearly the negative ion contribution, measuredat the substrate position, decreases for a moreeroded target.A simple geometric calculation allows tounderstand the trend.

15


9


Quantification of the negative ion fluxStrong correlation is found between EPA and negative ion intensity.

So, the negative ions brings the major fraction of all energy to the surface of the energy probe. For a fresh target this 28.8 mW/cm2

100

80

60

40

20

0

norm

alis

ed e

nerg

y flu

x

100806040200

normalised negative ions intensity

How to understand this line ?

At strong target erosion, the energy flux is defined by other effects.So the off-set is a measure for this energy contribution.

We estimate this at 8 mW/cm2 which is in reasonable agreement with the estimation based on TiN and Cu experiments (11.5 ± 3 mW/cm2

)

16



Quantification of the negative ion flux

We know the argon ion current density at the target,the average energy of the ions,but we don’t know the negative ion yield.Reversing the calculation, we get a yield of approximately 0.0057.Similar values are found in literature*

To the best of our knowledge, we believe this is the first quantitative estimate of the negative ion flux.

8

6

4

2

0

ion

-to-

ato

m r

atio

2.52.01.51.00.50.0

erosion depth (mm)

As the deposition rate was measured, it is possible to quantitatively define the ion-to-atom ratio.

For a flat target, the energy flux is approximately 28 mW/cm2.The energy flux can be calculated as YOIArEO.

*Tucek, J.C. and R.L. Champion,On the dynamics of secondary-electron and anion emission from an Al/O surface.Surface Science, 1997. 382(1-3): p. 137-146Tucek, J.C., S.G. Walton, and R.L. Champion,Ion-induced secondary electron and negative ion emission from Mo/O. Surface Science, 1998. 410(2-3): p. 258-269

Van Steenberge, S., W.P. Leroy, A. Hubin, and D. Depla, Momentum transfer driven textural changes of CeO2 thin films. Applied Physics Letters, 2014. 105(11).111602

17


10


Selection by ion bombardment

(200)(222)

The projected surface density depends on the crystal orientation.

In metallic mode : zone T : (200)In oxide mode : zone II : high negative ion bombardment : (200)In oxide mode : zone II : low negative ion bombardment : (111) (lowest surface energy)

(220)

1.0

0.8

0.6

0.4

0.2

0.0

pref

eren

tial c

ryst

allin

e or

ient

atio

n

2.52.01.51.00.50.0

racetrack depth (mm)

[111] [200] [220]

18



Case study 3 : Deposition of HEA

Definition

Influence of the deposition parameters and composition

19


11


High entropy alloys : definitionBoltzmann hypothesis:

∆S R c ln c Rln n

∆G ∆H T∆S

simple solution structures:crystalline FCC/BCC or amorphous

Yeh, J.W., S.K. Chen, S.J. Lin, J.Y. Gan, T.S. Chin, T.T. Shun, C.H. Tsau, and S.Y. Chang, Nanostructured high-entropy alloys with multiple principal elements: Novel alloy design concepts and outcomes. Advanced Engineering Materials, 2004. 6(5): p. 299-303

Gludovatz, B., A. Hohenwarter, D. Catoor, E.H. Chang, E.P. George, and R.O. Ritchie, A fracture-resistant high-entropy alloy for cryogenic applications. Science, 2014. 345(6201): p. 1153-1158

In bulk : fast quenching rates are needed.

Magnetron sputter deposition : a natural fast quenching rate. So ideal to grow these complex materials.

20



How to produce them ?preparation of the target

+ cold pressing+ + =+

no limits on composition

low cathode power

Fixed deposition conditionspumping speed: 125 l/sgas flow: 30 sccm Ardischarge current: 0.09 Aaverage film thickness: 500 nm

Parameter spaceAr gas pressure: 0.40 – 0.55 Patarget-substrate distance: 7 – 9 – 11 cmTarget composition for NbxCoCrNiFeCuTarget composition for AlxCoCrNiFeCu

21


12


AlxCrCoFeNiCuWithout Al, a clear FCC structure is noticed.

Al fraction increases lattice distortion of FCC structure increasespacking fraction of BCC is lower, incorporation of the large Al atoms

FCC BCC structure transition

Braeckman, B.R., F. Boydens, H. Hidalgo, P. Dutheil, M. Jullien, A.L. Thomann, and D. Depla, High entropy alloy thin films deposited by magnetron sputtering of powder targets.Thin Solid Films, 2015. 580(0): p. 71-76

22


XRD measurements


NbxCrCoFeNiCu

FCC amorphous transition

elementatomic

radius (pm)crystal

structurevalence

electrons

Al 143 FCC 3s23p1

Nb 143 BCC 4d45s1

Also the electronic structure determines the transition

The microstrain is a good indicator for the transition.But clearly also the deposition conditions affect the microstrain.But this does not fit with the EPA concept.

6.0

5.5

5.0

4.5

4.0

3.5

3.0

p·d

(Pa·

cm)

20151050at.% Nb

2.8

2.7

2.6

2.5

2.5

2.5

2.4

2

.4

2.3

2.2

2.2

2.1

2

1.9

1.8

1.8

1.7

1

.6

1.6

1

.5

1.4

1

.3

1.2

1.1

1

1

0.9

0.8

0.7

0.6

0.6

0.5

0.4

0.3

0.2

0.2

0.1

3.02.01.00.0microstrain (%)

60

50

40

30

20

10

EP

A (

eV/a

tom

)

2.4 3.4 4.4 5.4 6.4

p·d (Pa·cm)

0 % Nb 15 % Nb 5 % Nb 23 % Nb 10 % Nb

23


13


Influence of reflected neutrals

6.0

5.5

5.0

4.5

4.0

3.5

3.0

p·d

(Pa·

cm)

24201612840at.% Nb

8.8

8.75 8

.7

8.7

8.6

5

8.6

5

8.65

8.6

8.6

8.6

8.5

5

8.5

5

8.55

8.5

8.5

8.5

8.4

5

8.45

8.4

8.35

8.35

8.3

8.3

8.2

5 8

.2

8.1

5

8.1

8.1

8

8

7.9

7.9

7.7

8.88.68.48.28.07.87.6

film density (g/cm3)

24



Properties of HEAMaterial Contact

resistanceCoCrCuFeNi (p·d=2.80 Pa·cm) 395

CoCrCuFeNi (p·d=3.60 Pa·cm) 253

CoCrCuFeNi (p·d=6.05 Pa·cm) 71

Contact resistance depends on hardness which probably scales in a similar way as density(to be measured)

280

240

200

160

120

80

Ela

sti

c M

od

ulu

s (G

Pa

)

40x10-21

3530252015105

Momentum flux/Metallic flux (kgm/s)

16

12

8

4

0

Hard

ne

ss (G

Pa)

elastic modulus hardness

70

60

50

40

30

20

10

0

refl

ecti

on@

880n

m (%

)

8x10-22

76543Msp+refl (kgm/sTi)

Ar series Kr series

Mahieu, S., W.P. Leroy, K. Van Aeken, M. Wolter, J. Colaux, S. Lucas, G. Abadias, P. Matthys, and D. Depla, Sputter deposited transition metal nitrides as back electrode for CIGS solar cells. Solar Energy, 2011. 85(3): p. 538-544

TiN

TiN

25


14


Case study 4 : Inclined surfaces

Deposition set-up

Biaxial texture

Compositional gradients

26




Y

Zr

O2 flow

Sample

Chamberconditions

Y Zr

T-S distance [mm] 80-240 90

Current [A] 0.2 0.5

Pressure [Pa] 0.5

Substrate Glass / Si

Lamas, J.S., W.P. Leroy, Y.G. Lu, J. Verbeeck, G. Van Tendeloo, and D. Depla,Using the macroscopic scale to predict the nano-scale behavior of YSZ thin films.Surface & Coatings Technology, 2014. 238: p. 45-50Lamas, J.S., W.P. Leroy, and D. Depla,Influence of the target-substrate distance on the growth of YSZ thin films. Surface & Coatings Technology, 2014. 241: p. 26-29Lamas, J.S., W.P. Leroy, and D. Depla,Influence of target-substrate distance and composition on the preferential orientation of yttria-stabilized zirconia thin films. Thin Solid Films, 2012. 520(14): p. 4782-4785Lamas, J.S., W.P. Leroy, and D. Depla,The fictional transition of the preferential orientation of yttria-stabilized zirconia thin films. Thin Solid Films, 2012. 525: p. 6-12

27


15


Texture

A SZM transition ?

30 40 50 60 70

68

88127147167187207227

234

at% YDistance [mm]

254

Inte

nsi

ty (

a.u

.)

8

11

16202529334050

61

[400][222][311][220][200][111]

2 (°)

Doubtful because we stay in metal regime.

28



Pole figures

(111) Pole figures

(200) Pole figures

Yttrium concentration increases

Pole figure : 2D-map of the diffracted intensity from a (hkl) plane as a function of χ and φ (the sample orientation)

A few conclusions :

1) The film shows biaxial alignment2) A clear tilt of the [200] direction is noticed.

29


16


Biaxial textureUniaxial aligned thin film, i.e. a thin film consisting of crystallites with a preferential out-of-planeorientation

Biaxial aligned thin film, i.e. a thin film consisting of crystallites with a preferential out-of-planeorientation and a preferential in-plane orientation.

All you need is a tilted substrate.

30



SEM analysis

Zone T – [200]

SEM confirms the tilt

31


17


DF/STEM & STEM/EDXA (240 mm) B (160 mm) C (120 mm) D (90 mm)

32



Model

31arcsin

2 2Y ZrH r r C

a x

2 1 01 3

2

T T

h

/ / 0

31

2Y ZrC r r

a

Timoshenko, S., Analysis of bi-metal thermostats. Journal of the Optical Society of America, 1925. 11(3): p. 233-255

33


18


Conclusions

The EPA concept still seems a valuable tool tounderstand thin film growth during reactivemagnetron sputter deposition.

But it can be masked by• the presence of the negative ions as in the

case of CeO2. These species influence thetextural growth due to their high momentum.

• a change in composition for HEA• simply a certain deposition geometry as for

dual reactive sputtering

6.0

5.5

5.0

4.5

4.0

3.5

3.0

p·d

(P

a·c

m)

24201612840at.% Nb

8.8

8.75

8.7

8.7

8.6

5

8.6

5

8.65

8.6

8.6

8.6

8.5

5

8.5

5

8.55

8.5

8.5

8.5

8.4

5

8.45

8.4

8.35

8.35

8.3

8.3

8.2

5 8

.2

8.1

5

8.1

8.1

8

8

7.9

7.9

7.7

8.88.68.48.28.07.87.6

film density (g/cm3)

34



Conclusions and acknowledgementsSigelinde Van Steenberge

CeO2

Bert Braeckman

High entropy alloy deposition

Francis Boydens

Hydroxyapatite

Anna Ivanova

YSZ

Jérika Lamas (now at ULB)

Special research fund

Flemish Science Foundation

35


texture development during thin film magnetron sputter...

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