Characterisation, Optimization and Tuning of Plasma ...Vasile Vartolomei K. Matyash R. Schneider C....

1

Characterisation, Optimization and Tuning of Plasma

Parameters in ICP discharge

Vasile Vartolomei

K. MatyashR. SchneiderC. Wilke

M. HannemannR. Hippler H. KerstenA. Knuth

Institute of PhysicsFelix Hausdorff Str. 6D-17489 GreifswaldGermanyvartolomei@physik.uni-greifswald.de

2

OutlookOutlook

Capacitive effect in ICP: how to reduce it?

Interpretation of Ion Distribution Function

Tuning-optimising the IDF

Energy balance to substrate

Conclusions

© V. Vartolomei: Graduate Summer Institute ‘‘Complex Plasmas‘‘ August 5. 2008 Hoboken, NJ (USA)

3

MotivationMotivation

What we want ...

ne Te eVi n*EE

DF

Electron energy

EEDF Species

N.Braithwaite (DPG-Spring Meeting Aachen 2003)


4

MotivationMotivation

What we have ...

RF Power 2FlowPressureRF Power 1

Timer

O2 N2 CH4 CF4


Experimental deviceExperimental device

Region I

Region II

Sputtered Target and gas inlet

RFEA andLangmuir probe

Grid(with/without)

RFEA andLangmuir probe

Region II

Region I

Sputter target

Grid(without/with)

Gas: Argon

Power range: 100 - 600 W

RF frequency: 13.56 MHz

Magnetic field: 0 - 2.2 mT

Pressure range: 6×10-4 – 1×10-2 mbar

5


6

Capacitive effect in ICPCapacitive effect in ICP

Capacitive effects produces undesiredsputtering effects at the coil

Reduce RF amplitude:Balance the coil and get a factor 2 reduction!

G. K. Vinogradov, Transmission line balanced inductive plasma sources, Plasma Sources Sci. Technol. 9 (2000) 400-412


7

Reduce capacitive effect: step down transformerReduce capacitive effect: step down transformer

3 Capacitive effects produce undesiredsputtering effects at the coil

Balanced coil


8

Reduce RF amplitude: add magnetic fieldReduce RF amplitude: add magnetic field

RF

ampl

itude

at c

oil e

nds

Normalised Magnetic Field


9

→

B

The ECWR effectThe ECWR effect

Bz = B(t), By = B = constant

B

B(t)B

λplasma=λvac/nR

stationary wave

H.Oechsner et al., Thin Solid Films 341 (1999), 101-104)


10

The ECWR effect: Plasma DensityThe ECWR effect: Plasma Density

0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.80.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

0.6 x 10-3 mbar 2.0 x 10-3 mbar

Magnetic Field [mT]

Nor

mal

ised

Pla

sma

Den

sity


11

Reduced capacitive effectReduced capacitive effect

Magnetic Field [mT]

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

100 W 300 W 500 W

RF

bias

(V)

coil current (A)


12

Experimental measurement of IDFExperimental measurement of IDF

Collector characteristic

-50 0 50

-0.6-0.4-0.20.00.20.40.60.81.01.21.41.61.82.02.22.42.62.83.0

I c(a.

u.)

Uc(V)


13


Retarding Field Energy Analyser (RFEA)

dIc/dUc α IDF

A

I

-100 -75 -50 -25 0 25 500,00

0,04

0,08

0,12

0,16 Selector = - 75 V Selector = -100 V

IDF

[a.u

.]

Ion Energy [eV]-180 -150 -120 -90 -60 -30 0 30 60

0,0

0,3

0,6

0,9

Selector = - 75 V Selector = - 100 V

Col

lect

or C

urre

nt [1

0-6 A

]

Collector Voltage [V]


14


IDF α dIc/dUc

∫+∞

=0

)( ndvvf

dEEgdndvvf )()( ==

∫ ∫== dEvfMedvvvfeI

ii )()(

⎟⎟⎠

⎞⎜⎜⎝

⎛−=⎟

⎠⎞

⎜⎝⎛−=

c

cii

dUUdI

eM

dEEdI

eMvf )()()( 2

Where is the Plasma Potential ?Four points of view…

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

dIc/d

Uc(

a.u.

)

U c(V)

A: Lipschultz, I. Hutchingson, B. LaBombard, A. Wan, Electrical probes in plasmas, J.Vac.Sci.Technol. A 4(3), p.1810-1816 (1986)

B: S. G. Ingram, N. St. J. Braithwaite, Ion and electron energy analyser at a surface in an RF discharge,

J.Phys.D.: Appl.Phys. 21, 1496-1503, (1988)


15

IDF model 1 (point A)IDF model 1 (point A)

a) in plasma

b) at the pre-sheath entrance

c) at the wall

Ion Velocity Distribution Functionone-dimensional (gaussion)

Allows to calculate ion temperature!


16

IDF model 4: K.U. RiemannIDF model 4: K.U. Riemann

c

zxλ

=e

zi

KTvmy

2

2

=

eKTeU

−=ϕIon Temperature and Plasma potential information are lost

∫∞

−+ =

0

2/1 ),( dyyxfyn


17

PIC-MCC simulationPIC-MCC simulation

0 10 20 30 40 50 60 70 80 90 100 110 120 1300

5

10

15

20

25

30

35

40

45

50

55

60

65

Vp(V)

Z, λd0 10 20 30 40 50 60 70 80 90 100 110 120 130

0.0

0.5

1.0

1.5

2.0

2.5

electrons ions

ne,ni 109 cm-3

Z, λd

Known input data: Plasma potential, Ion temperature and Electron temperature

Run the code and see how they come to the wall


18

PIC-MCC simulationPIC-MCC simulation

IDF maxima is the plasma potentialsince we have 10% oscillations in Vp.

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.20.0

0.2

0.4

0.6

0.8

1.0IED

Ei,kin/eVp

Zwall-cell Zwall-2xλDebye-cell Zwall-3xλDebye-cell Zwall-4xλDebye-cell


19

Influence the transport between the two Regions: add a gridInfluence the transport between the two Regions: add a gridID

F [a

.u.]

10 15 20 25 30 35 40 450

50

100

150

200

250

Ion Energy [eV]

Region I

Region II

Grid

Origin of double peak structure ?


20

First Concept: Collisionless rf modulated sheathFirst Concept: Collisionless rf modulated sheath

C. Charles at al, Physics of Plasmas 7 (12), 2000K.Köhler at al, J. Appl.Phys. 58 (9), 1985

1

21

Experimental Contradiction of First ConceptExperimental Contradiction of First Concept

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

RFEA 0 degree to axis, d ist=49 m m RFEA 90 degree to axis, d ist=54 m m

400W, 0.6×10-3 mbar

IDF

[a.u

.]

Ion Energy [eV]

Region I

Region II

1.

2.

1.

2.


22

Second Concept: Space potential differenceSecond Concept: Space potential difference

Axial dependence

Ion

Ene

rgy

(eV

)

Region I Region II

Vplasma (V)

Z (cm)10 15 20 25 30 35 40 45

0

50

100

150

200

250

IDF

[a.u

.]

Ion Energy [eV]

Double peak structure in IDF Explains the contradiction


23

Tuning the Ion Distribution FunctionTuning the Ion Distribution Function

• Can one move the Low Energy Peak ?

• Can one move the High Energy Peak ?

• Can one move them independently ?


24

Apply voltage on gridApply voltage on grid

Build a variable gate

Region II

Sheath

Grid wire

electrons

Region I


25

Biased GridBiased Grid

Grid bias [V]

Influence on plasma potential in Region II

-40 -30 -20 -10 0 10 20

8101214161820222426283032343638 400W, resonance

Pressure (10-3mbar): 0.6 2.0 6.0 10.0

Plas

ma

Pote

ntia

l [V] × 10

-3mbar


26


Influence on plasma density in Region II

-40 -30 -20 -10 0 10 200,00E+000

1,00E+009

2,00E+009

3,00E+009

4,00E+009

5,00E+009

6,00E+009

7,00E+009

8,00E+009

9,00E+009

1,00E+010

400W, resonancePressure (10-3mbar):

0.6 2.0

Grid bias [V]

Elec

tron

Den

sity

[cm

-3]

× 10-3 mbar


27


0 5 10 15 20 25 30 35 40 45 50 550.00

0.01

0.02

0.03

0.04 Ugrid:

0 V -20 V -100 V

IDF

[a.u

.]

Ion Energy [eV]

HEP

LEP Bias Grid:

Influence on Low Energy Peak (LEP) in Region II


28

Apply DC Bias on Inductive CoilApply DC Bias on Inductive Coil

-5 0 5 10 15 20 25 30 35 40 45 50 55 60 65

0,00

0,02

0,04

0,06

Ugrid=0V, Grounded coil ! Ugrid=0V, Floating coil Ugrid=-100V, Floating coilID

F [a

.u.]

Grid bias [V]Shift and form change of IDF in Region II


29

Three peak structure?Three peak structure?


30

Energy Flux to SubstrateEnergy Flux to Substrate

shield

copperplate

(substrate)

thermalcouple

substratebiasing

andsaturation

current

insulation(marcor)

rod(movable)

⋅ += outSin QHQPlasma ON (heating)

outS QH +=•

0Plasma OFF (cooling)

dtdTmcH SS =

•

Tcool

S

heat

SSSin dt

dTdt

dTmccoolHheatHQ⎩⎨⎧

⎭⎬⎫

⎟⎠⎞

⎜⎝⎛−⎟

⎠⎞

⎜⎝⎛=−=

••

)()(

( )dAJJJJJJdAJQSuSu A

photoncondneurecieA

inin .∫∫ +++++==


31


0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.00.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11

0.12

100 W

200 W

300 W

400 W

500 W

600 W

Mea

sure

d En

ergy

Flu

x [J

s-1 c

m-2

]

pressure [×10-3mbar ]

Higher energy contribution at low pressure


32


0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.00.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11

0.12

100 W

200 W

300 W

400 W

500 W

600 W

Mea

sure

d En

ergy

Flu

x [J

s-1 c

m-2

]


Higher energy contribution at low pressure


33

Energy Flux to Substrate: ModellingEnergy Flux to Substrate: Modelling

400 W

0 1 2 3 4 5 6 7 8 9 10 110.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08 Measurement Ji+Je+Jrec (model) Ion energy flux Ji Electron energy flux Je Recombination energy Jrec

Mea

sure

d En

ergy

Flu

x [J

s-1 c

m-2

]


Missing contributions


34

Energy Flux to Substrate: Bias influence on thermal probeEnergy Flux to Substrate: Bias influence on thermal probe

-80 -70 -60 -50 -40 -30 -20 -10 0 10 200.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

0.055

0.060

0.065

measurement modelling

300 W, 4×10-3 mbar

Voltage on Thermal probe [V]

Ener

gy F

lux

[Js-

1 cm

-2]

Possible reasons:

- Plasma Radiation

- Excited atoms

- Fast neutrals

important heating chanell


35

Fast neutralsFast neutrals

Generation of fast neutrals by one ion by several charge-exchange collisions:

cascade

Substrate

n

2

1

z

Z = 0

E

1Z

2Z

nZ

trajectories: ion - continuous linefast neutrals - interrupted lines

Large difference between cross sections of collision processes:

- ion-neutral collision (CX)

- fast neutral – neutral elastic collision

Many fast neutrals for one ion !

Including this effect gives good results


36

Energy Flux to Substrate: ModellingEnergy Flux to Substrate: Modelling

0 1 2 3 4 5 6 7 8 9 10 110.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08 Measurement Ji+Je+Jrec (model) Ion energy flux Ji Neutral energy flux Jn

400 W

Mea

sure

d En

ergy

Flu

x [J

s-1 c

m-2

]

pressure [×10-3mbar ]Better agreement


37

ConclusionsConclusions

Capacitive effects in ICP

How to understand the IDF…

Tuning-optimising the IDF:

Grid effect and how to move LEP and HEP

Energy balance to substrate: fast neutrals


Characterisation, Optimization and Tuning of Plasma ...Vasile Vartolomei K. Matyash R. Schneider C....

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