· disadvantages: complex target design outline motivation background examples exercise 8...

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Simulation of

Metal

TRAnport

SIMTRA : a tool to predict and understand deposition

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

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1) Motivation : Why do we calculate ?2) Scientific background : How do we calculate ?3) Examples : What can we calculate ?4) Some conclusions

Outline

K. Van Aeken, S. Mahieu, D. Depla J. Phys. D: Appl. Phys. 41 205307 (2008)

OutlineMotivationBackgroundExamplesExercise

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Motivation

The results of each deposition technique is a thin film with given properties

A few relevant properties are thickness, crystallographic orientation, morphology, density, composition, …

All depend on : - the type of arriving species- the properties of the particles (charge, energy, …)- the number of arriving particles

The major players are of course the film forming particles

So SIMTRA is developed to predict the number and the properties of the particles leaving the source and arriving at the substrate.

The code is optimized for magnetron sputter deposition (see further)


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Motivation

Why developing a new simulation code ?

-Most codes are research group specific.-Most codes are hard to access .-Most codes are not user-friendly. They miss a good interface to assist the user.

An easy to access program (www.draft.ugent.be )with a simple interface (three VB sheets)is the answer.


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Scientific background : magnetron sputter deposition

Magnetron sputter deposition is based on a magnetically assistedgas discharge

Source materials is the cathode, or targetDischarge voltage : order 400 VWorking pressure (argon gas) :1x10-3 tot 1x10-2 mbar

Behind the cathode magnetsare placed. In this way the gas discharge can bemaintained at lowerpressures.Reason : higher depositionrates


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Scientific background : magnetron types

2 inch diameter cathodeCilindrical planar kathodeLab scale

2’’

15’’

4 1/3’’ Rectangular planar cathodeIndustrial scale

Intrinsic disadvantages : Formation of an erosion groove

Less stable in reactive mode

Advantages : simple target design


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Scientific background : magnetron types

Rotating cylindricalmagnetron

18 cm : but can be extended

5 cm

45 cm

14 cm

Advantages : Stable in reactive modeNo erosion groove (i.e. longer lifetime)

Disadvantages : Complex target design


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Scientific background : Target erosion : starting points of the sputtered

particles

Cooperation with VITO


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Scientific background : sputtering

Magnetron sputter deposition is an PVD technique

Physical Vapour Deposition

The production of a vapour by a physical process. Thisprocess is sputtering.Ions from the plasma hit the target, and target atoms are ejected. These move towards the substrate to form the film.


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Scientific background : sputtering

0.001

0.01

0.1

1

10

sputter yield

10 100 1000 10000 100000

ion energy (eV)

The number of atoms sputtered per ion depends on the material and the discharge voltageFor metal : 0.5 to 2 (Al to Cu)For oxides : much lower 0.07 (Al)


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Scientific background : angular distribution of sputtered particles

Heart-like emissionDeviation from cosine

Propose differential yield :

∑=

=Ω

5

12

2

cos)(i

i

ic

d

Ydθθ

Fit coefficients ci from thesimulated deposition profilesof an angular base set

Nascent angular distribution :


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Scientific background : energy distribution1.0

0.8

0.6

0.4

0.2

0.0

relative number density

0.001 0.01 0.1 1 10 100

energy copper atoms (eV)

Copper evaporated at 1300 K

Copper sputtered by 300 eV Ar+

Thompson distribution SRIM energy distribution

Usb/2

average energy of sputtered particles


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Scientific background : sputter yield

To calculate a deposition rate, the sputter yield of the material must be known.

What yield to use ?Sputter yields Cu

0.5

1

1.5

2

2.5

200 300 400 500 600 700

Vd of Ei

Yield

exp

Yam model

Tridyn

srim

We decided to measure them.


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Scientific background : reactive magnetron sputtering

Magnetron sputer deposition allows to deposit compounds.

Oxides, nitrides : generally no conductivetarget available

Solution : the reactive gas is added to the discharge

Reaction occurs mainly on the substate, but at sufficient high reactive gas flows also on the target.

-

reactive gas : O2

SN N

+

Target

Ar-ions

Consequences ?


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Scientific background : reactive magnetron sputtering

390

380

370

360

350

340

330

target voltage (V)

1.41.21.00.80.60.40.20.0

oxygen flow (sccm)

300

250

200

150

100

50

depositio

n ra

te (m

ass unit/s

)

/ target voltage / deposition rate

full symbols : additionopen symbols : removal

Reactive deposition of TiO2


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Scientific background : SIMTRA

Calculate free path length

High energy

Near thermal energy

Thermal

Initialization Generate particles-planar : radial erosion profile-cylindrical : measured or simulated erosion profile

BoundaryImplements geometry

Does particles’ trajectory intersects surface before collision ?

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 +


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NOBoundary

Implements geometryDoes particles’ trajectory

intersects surface before collision ?

Describe collision :Calculate scattering angle

Calculate new velocity

com com2

R 2

2

com

1(E ,p) 2p dr

V(r) pr 1

E r

∞

θ = π −

− −∫

Go back to free path calculation

YES

Deposition

Generate new particle


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com com2

R 2

2

com

1(E ,p) 2p dr

pr 1

E r

V(r)

∞

θ = π −

− −∫


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Internuclear distance r (Å)Interatomicpotential (eV)

Internuclear distance r (Å)Interatomicpotential (eV)

Screened Coulomb potential :Only repulsive !

Quantum-mechanical potentialsAttractive and repulsive(only Cu-Ar and Al-Ar)


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Examples : Verification of the code ?

The Metal Flux Monitor

C. Eisenmenger-SittnerM. Horkel

Angular distribution of metal flux Thickness Profile

Pinhole Camera : A particle that passes the orifice (diameter 1mm) at

a given angle x impinges the substrate a the position y


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Examples : Verification of the code ?

Comparison Cu at variable pressures

Comparison Al at variable pressures


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Examples : Deposition rate distribution for a rotating magnetron

Measure deposition rate with a

quartz crystal microbalance for :

Cu, Ti, Al target

Ar pressure : 0.3, 0.6 and 1 Pa

as function of θ at : 3 radial distances : r1,r2,r3 3 z-positions : z1,z2,z3

⇒Outward radial metal flux (r,θ,z)

Compare to simulation

Al, 0.3Pa Ar

r = r2, θ = -30°, z = z2Vd = 357 V, I = 0.45 A

Example :


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Examples : Deposition rate distribution for a rotating magnetron

P = 0.3 Pa

r = r1

Spatial dependence Pressure dependence :

r = r1z = z2


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Examples : A simple thing to start

We can expect that the deposition rate decreases as a function of the target-substrate distance.What is the relationship ? We expect a 1/d2 relationship at sufficient high pressure. Well, let us test this idea with SiMTRA

A planar circular

magnetron (2inch)

mounted in a cubic

vacuum chamber

(1x1x1 m). The

substrate was a circular

plate of 1x1 cm placed

under the target centre

at several distances.

The target material was

aluminum.

Using an output file of SIMTRA and MatLab one can check the configuration


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Examples : A simple thing to start

60000

50000

40000

30000

20000

10000

0

5.568101520100

0.0001 0.005 0.01 0.015 0.02 0.025 0.03 0.033

0.1 Pa

0.3 Pa

0.6 Pa

0.9 Pa

d-2 (cm

-2 )

target-substrate distance d (cm)

number of arriving particles

Seems to fit quite well.


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Examples : Prediction of the composition for dual planar magnetrons

Experimental set-up

Thanks to M. Saraiva


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•Discharge current

Mg, Cr = 0.5 A

•Source-sample distance

•Oxygen flow

Mg-Cr-O

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14

12

10

8

09121316192125273241

20

18

16

14

12

10

850403020100

7

6

5

4

3

2

4952525254545758605959

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14

12

10

8

1008175736558504133220

target position Mg

target position Cr

oxygen flow

Mg concentration (%)

Cr concentration (%)

O concentration (%)

target-sample distance (cm)

oxygen flo

w (sccm)

Mg metal ratio (%)

composition


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100

80

60

40

20

0100806040200

100

80

60

40

20

0100806040200

100

80

60

40

20

0100806040200

100

80

60

40

20

0100806040200

100

80

60

40

20

0100806040200

M/(M+Mg) %

(R'/(R'+1))x100

Mg(Al)O Mg(Cr)O Mg(Ti)O

Mg(Y)O Mg(Zr)O

open symbols : experimental

closed symbols : SiMTRA

: fitted line through the experimental points


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Examples : Prediction of the composition for dual rotating

magnetrons

Setup:

Cu - target Al - targetshield in order

to minimize

re-deposition

discharge


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Examples : Prediction of the composition for dual rotating magnetrons

Simulation : Separate calculation for both magnetronsUsing correct sputter yields for Al and CuCalculate the composition

Experiment : Measuring Cu/Al using EPMA and EDX


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Examples : Prediction of the composition for dual rotating magnetrons

100

80

60

40

20

0

at. %

Cu

50403020100

distance from chamber wall (cm)

0.3 A exp

0.3 A SiMTRA 0.6 A exp

0.6 A SiMTRA 0.9 A exp

0.9 A SiMTRA

1.0

0.8

0.6

0.4

0.2

relative # of atoms arriving at substrate

50403020100

distance from chamber wall (cm)

Al exp

Al SiMTRA Cu exp

Cu SiMTRA

Deposition of Cu-Al: SiMTRA vs.

experiments

• discharge current

Cu = 0.3 A, Al = 0.3 - 0.9 A

• source-sample distance = 9.5 cm

• SiMTRA can be used to predict

composition in a dual magnetron

setup

Thanks to F. Boydens


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Examples : Reactive magnetron sputtering : condition of the substrate

tθ

t1 θ−

cθ

c1 θ−

F

F1

F2

F4F3

The composition at the substrate is defined by the deposition rate on the substrate, and the reactive gas pressure

( ) ( ) ( )c

c

t

tMc

c

t

tNccA

A1Y

e

J1

A

AY

e

J1F20 θθ−

−θ−θ

+θ−α=

Homogeneous deposition and steady state conditions:


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( ) ( ) ( )c c,i N t t c,i M t td c, ,i ,i d i

J J0 2 F 1 Y A 1 Y 1 A

e ef f

= α − θ + θ − θ − − θ θ

Subdivide the substrate in several cells and the condition of cell i can be calculated by

The fraction fd,i of sputtered atoms arriving at each cell i can be calculated with SiMTRA. So, we included the output of SiMTRA in another simulation tool (also available at www.draft.ugent.be) RSD2009.


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0.37

0.35

0.33

0.31

0.29

Total pressure (Pa)

3.02.01.00.0

Oxygen flow (sccm)

Blue : metalRed : oxide

Thanks to Wouter Leroy


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Examples : Negative oxygen emission

M+

O-

Masspec

Y or Al

P(Ar) 0.4 PaP(O ) 0.04 Pa2

8 cm

Measurement of negative oxygen emission during reactive magnetron sputtering


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100

101

102

103

104

Cps (a.u.)

25020015010050E (eV)

exp O SiMTRA O2 SiMTRA

YO SiMTRA YO2 SiMTRA O-

O2

- =>

O + O-YO

- =>

Y + O-

YO2

- =>

YO + O-

100

101

102

103

104

Cps (a.u.)

30025020015010050 E (eV)

exp O SiMTRA O2 SiMTRA

AlO SiMTRA AlO2 SiMTRAO

-

O2

- =>

O + O-

AlO- =>

Al + O-

AlO2

- =>

AlO + O-

VYOM

OMxV

VYOM

OMxV

VOM

OMxV

VOM

OMxV

d

d

d

d

5.24)(

)(

28)(

)(

5.92)(

)(

185)(

)(

2

2

=

=

=

=

VAlOM

OMxV

VAlOM

OMxV

VOM

OMxV

VOM

OMxV

d

d

d

d

78)(

)(

108)(

)(

145)(

)(

290)(

)(

2

2

=

=

=

=

Simulation of the energy distribution


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0°10°

20°

-30° 30°

-20°

-10°

Massp

ec

Masspec

Masspec

Masspec

Masspec

Masspec

Massp

ec

Direction of the negative ions.


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'O exp' 'O SiMTRA' 'O/Al SiMTRA (a.u.)' 'magnetron'

0°10°

20°

-30° 30°

-20°

-10°

Al Y

'O exp' 'O SiMTRA' 'O/Y SiMTRA (a.u.)' 'magnetron'

0°10°

20°

-30° 30°

-20°

-10°

Thanks to Stijn Mahieu


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Examples : momentum flux

Opening area ATorsion plate

Torsion wire

reflector

Front view Back view

Measure steady state rotation angle => know momentum flux


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Examples : momentum flux

15

12

9

6

3

Hardness (GPa)

40x10-21

3020100

Measured Mtot (kgm/s)

Contribution of backscatter ions, sputtered neutrals to the total momentum flux can be calculated using SIMTRA


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Examples : Biaxial aligned thin films

Out-of-

planeGrain boundary

In-

plane

Only preferred out-of-planeorientation : uniaxialalignment

Out-of-

planegrain

boundary

In-

plane

Preferred in-plane and out-of-plane orientation: biaxialalignment

FWHM

XRD pole-

figures


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Examples : Biaxial aligned thin films

Zone T growth: as seen in plan view

- growth rate anisotropy due to anisotropy in capture cross-section

of incoming adatoms

Direction of

incoming

material

Capture length

(111)

(111)

(111)

(111)

Sketch of plan view


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Examples : Biaxal aligned thin filmsOutlineMotivationBackgroundExamplesExercise

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Conclusion

The code can give an answer to quite some questions related to

Deposition rateCompositionEnergy of deposited sputtered particlesAnd probably you can invent a few more …

In that case, or if you wish to cooperate on this projectwe are ready to assist you …

Contact : [email protected]

Cost of SiMTRA : A scientific return in joint papers is a good alternative for money.

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Exercise : vacuum chamber

The influence of a shutter on the deposition profile.

Set-up

Cylindrical vacuum chamber : diameter : 60 cmlength : 50 cm

60 cm

50 cm


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Exercise : gas element, pressure, temperatureOutlineMotivationBackgroundExamplesExercise

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Exercise : the source Lab magnetron 2”OutlineMotivationBackgroundExamplesExercise

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Exercise : the source : position

60 cm

50 cm

The centre of the axis is in the middle of the magnetron

So, in the middle of the vacuum chamber lidand z=0.035 m


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Exercise : let’s make a cylindrical substrate

1 cm

2 cmThis object consists of 3 surfaces !1) Plane piece : outer boundary circle2) Cylindrical piece3) Plane piece : outer boundary circle

This tells to SIMTRA where the surfaces are located in the reference system of the object (see manual, and next slide)


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Exercise : the position vectors for the substrate

2 cm

x’

z’

y’

Reference system of the object

c

a

b-0.005-0.010

-0.00500.01

-0.00500


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2 cm

x’

z’

y’


c

a

b

0.0050.010

0.00500.01

0.00500


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2 cm

x’

z’

y’


-0.0050.01

+0.00500

-0.00500


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Exercise : position the substrate

60 cm

50 cm

X : 0Y : 0Z : 0.175 m

10 cm

Magnetron length : 7 cmCentre of the substrate : 0.5 cmAnode-substrate top surface : 10 cm


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Exercise : check the output : Matlab file : plotdepositie

This looks just great !


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Let us calculate : the deposition profile on the top surface

2.0

1.5

1.0

0.5

0.0

2.01.51.00.50.0

Yellow is zero.

What is the effect of the pressure ?

1 4 7

10

13

16

19

22

25

28

R1

R4

R7

R10

R13

R16

R19

R22

R25

R28

20-25

15-20

10-15

5-10

0-5


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Repeat the simulations at different pressures

45x103

40

35

30

25

20

15

10

5

number of arriving atoms

86420

argon pressure (Pa)


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Including a shutter …

The shutter is built from a rod and a circular disk.

60 cm

50 cm

The rod is 38 cm long and has a diameter of 1 cm. Make it.

The position of the rod is 2 cm off centre, and connected to the back of the chamber


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Including a shutter …(2)

The shutter is built from a rod and a circular disk.

60 cm

50 cm

The disk is 10 cm in diameter and 1 mm thick. Make it…

Its centre is at 7 cm in X and 2 cm in Y, and connected to the rod.


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Exercise : check the output : Matlab file : plotdepositie

This looks just great !


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Repeat the simulations at different pressures

45x103

40

35

30

25

20

15

10

5

0

number of arriving atoms

86420

argon pressure (Pa)

no shutter

with shutter

The introduction of the shutter lowers the deposition rate as the shutter collects atoms which can not reach the substrate anymore.

But there is more …


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Let us look at the distributions

25

20

15

10

5

0

20100

0.25 Pa

25

20

15

10

5

0

20100

0.5 Pa

25

20

15

10

5

0

20100

1 Pa

25

20

15

10

5

0

20100

2 Pa

25

20

15

10

5

0

20100

3 Pa

25

20

15

10

5

0

20100

4 Pa

25

20

15

10

5

0

20100

5 Pa

25

20

15

10

5

0

20100

8 Pa

Distorted deposition profile …


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Let us look at the distributions

25

20

15

10

5

0

20100

Weighted centre position

Error…

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

off centre position (a.u.)

86420

pressure (Pa)

with shutter

without shutter

25

20

15

10

5

2520151050


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And what about the energy ?

0.01

2

4

6

0.1

2

4

6

1

2

4

6

10

average energy (eV)

8 9

0.12 3 4 5 6 7 8 9

12 3 4 5 6 7 8

pressure (Pa)

without shutter

with shutter

Thermal energy

· disadvantages: complex target design outline motivation background examples exercise 8...

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