It d ti tIntroduction to Non-thermal Reactive ...bonitz/si10/meichsner.pdf · polymer film (top)...

I t d ti tIntroduction to Non-thermal Reactive PlasmasNon thermal Reactive Plasmas

Jürgen MeichsnerU i it f G if ld I tit t f Ph iUniversity of Greifswald, Institute of Physics,Germany

DFG Collaborative Research Centre Transregio 24„Fundamentals of Complex Plasmas“

12nd Graduate Summer Institute Complex Plasmas, August 5 – 13, 2010, Greifswald, Germany

Outline

● Reactive plasmas – Overview

● Non-thermal plasmas

● Plasma boundary – plasma sheath

● Example oxygen cc-rf plasma

● Example fluorocarbon cc rf plasma● Example fluorocarbon cc-rf plasma

● Outlook

2

Out oo


Reactive plasmasOverview

Reactive plasmasReactive plasmas are a demanding, complex and highly application-oriented field which needs fundamental knowledge ofapplication oriented field which needs fundamental knowledge of plasma processes and plasma-surface interaction.

The situation is complicated due to the fact that reactive plasmasThe situation is complicated due to the fact that reactive plasmas represent a cross-disciplinary field which requires knowledge in the fields of

Plasma physics,

Plasma chemistry dPlasma chemistry, and

Materials science.

But above all, reactive plasmas represent a field with a fascinating variety of well-established processes and novel potential applications.

2nd Graduate Summer Institute Complex Plasmas, August 5 – 13, 2010, Greifswald, Germany 3

Low temperature plasma applications

Overview

Application Plasma acts as Example

l i l i h d i h i h

Low-temperature plasma applications

electrical switches conductor vacuum switches gas pressure switches

light sources radiation source low pressure: fluorescent lamp, sodium lamp

high pressure: Hg Xe Na lamp Halogen-metal-high pressure: Hg, Xe, Na lamp, Halogen-metal- vapor lamp, gas lasers (CO2, He)

material treatment heat source welding, melting (steel production), cutting, ....

deposition particle source sputtering, thin film deposition

surface modification particle source treatment of textiles, treatment of polymers

etching particle source dry etching of semiconductors

electrical gas cleaning particle source electrical filters (dust filters in exhaust of power plants)

plasma chemistry, thermal remediation of toxic waste

plasma chemistry,

non thermal

synthesis of chemical compounds (e.g. ozone production)

non-thermal


Multitude of scales in time and spaceOverview

Multitude of scales in time and space

10-1 m100 s

plasma bulkplasma striations diffusion,

collective behavior

10-6 m

10-3 m

10-3 s

100 s

particles

plasma sheathcollective behavior

of particles,phase transitions

10 6 m

10-9 m 10-6 s

10 s

thin surface layers,clusters

particlesradical reactions,

chemical processes

excitation, ionization, tt h t di i ti

10-10 m 10-9 s

c uste s

atoms,molecules

dynamic ion processes

attachment, dissociation

10-12 s

molecules

electron energy relaxation


ProblemOverview

ProblemL Multi species plasma

PLASMAL

λ

Multi species plasmapositive/negative ions, electrons, excited and reactive neutral species, nano/micro particles

λDe

λ

Plasma sheath

nano/micro particles, plasma radiation (photons)

δ

a

InterfacePlasma boundarymetal alloy

SOLIDd

a metal, alloysemiconductor,insulator (polymer, ceramics, glass)

d


Reactive plasma

Overview

L

ionisation, attachment, excitation, dissociation,ion-molecule-reactions, radical reactions

l h th h d i t tPLASMA

L

λ

plasma sheath - charged species transport

kinetic/internalenergy,λDe

λ

Plasma sheath charged atomsand molecules,

reflected andsecondary species,

momentum,charge,mass

δ

a

Interfaceand molecules,

reactive species,photons

secondary species,reactions products,sputtered species

adsorption/desorption, reflection, sputteringSOLID

d

a

adsorption/desorption, reflection, sputtering

recombination, dissociation, diffusion, radical reactions, secondary species formation

d

Plasma bo ndarPlasma boundary


Carrier gases - precursorsOverview

Rare gasesAr He

Carrier gases precursorsAr, He,…Simple molecular gasesO2, N2, H2,… ityO2, N2, H2,…HydrocarbonsCH4, C2H2,… pl

exi

4, 2 2,Fluorocarbons, gases containing halogensCF4, C2F4, C2F6, C3F8, C4F8, NF3, CHF3, CCl4, CHCl3,… C

om

4 2 4 2 6 3 8 4 8 3 3 4 3

Silane, organosiliconsSiH4, HMDSO, HMDSN,…

C

Hydrocarbons with specific functional groupsAcrylic acid (-COOH), Ethylene glycol (-OH),Ethylene diamine / Allyl amine (-NH2),…


Reactive Plasma – Surface InteractionOverview

Reactive Plasma Surface Interaction

Surface propertiesSurface propertiesSuper-hydrophobic

surface self-assembling reflectivitymicro turbulenceg

catalyticreactions

micro turbulence

LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLnano/micro-structured surface

thin filmfunctional groups

nanoparticles

thin film

b i fil b

Thin film properties

barrier films membranes sensors

9

Thin film properties


Overview

Nano- and micro-structured surfaces

Erosion / etching of surface material

Interaction deposition / etchingInteraction deposition / etching

Cluster-, particle deposition, p p


Overview

Chemical modification of material s rfacesChemical modification of material surfaces

Surfaces with specific molecular groupsSurfaces with specific molecular groupse.g. C-OH, -COOH, -C=O, -NH2, -CH3, -CF3

Synthesis of functional thin films e.g. a-C:F , a-C:H, -Si-O-Si-, SiOx, -Si-NH-Si-g , , , x,

Composite films with nanoparticlesComposite films with nanoparticlese.g. organic thin film with TiO2 nanoparticles


Overview

Partially hydrophilic surface Membrane from PP HMDSO

Plasma treatment of hydrophobic Porous polymer (polysulfone) and polyvinylidenfluoride

(water drops Ø 1.25 mm)200 nm thin pinhole free plasma

polymer film (top) from hexamethyldisiloxane.

C. Oehr, Fraunhofer-Institut für Grenzflächen- und Bioverfahrenstechnik, Stuttgart


Outline






● Outlook

13

Out oo


Temperature – Density – PlotNon-thermal plasma

p yLow-temperature Plasma

nebula

auroraaurora


Non-thermal plasma

Low-temperature plasmas

Thermal plasma Non thermal plasmaThermal plasmalocal thermodynamic equilibrium (LTE)

Non-thermal plasmanon-equilibrium plasma

Te = Tion = Tgas ≤ 104 K Te~104 K >> Tion ~ Tgas

104 K ≈ 1 eV

Electric gas discharge plasmas at

10 K ≈ 1 eV

high pressure atmospheric pressure low pressure


Non-thermal conditionsNon-thermal plasma

Non thermal conditionsTwo important consequences are due to the large difference in the mass of the electrons and ions (me / mp ≈ 1 / 2000):

(1) Electrons have at the same energy a much higher velocity than the heavyparticles and react much more readily to external fields.

(2) The energy transfer in elastic collisions between electrons and heavyparticles (ions, neutrals) is very low

a large number of elastic e – i and e – n collisions is required to equilibrate the energy.

As a consequence of point 2 low-pressure plasmas are not in thermal equilibrium because the externally applied energy is coupled to the electrons and they do not significantly heat the heavy particles.

While the electrons are hot (Te ≈ 1 to 10 eV) the heavy particles retain more or less the temperature of the surrounding walls.

f fTherefore, low-pressure plasmas are also often called non-equilibrium plasmas or cold plasmas.


Non-thermal plasma

ΔΔ

Momentum gain of neutral species in an elastic electron - neutral collision:

v een mp Δ⋅=Δ

Increase of the kinetic energy of a neutral species of the mass (m)

( ) eT

eT

ee

eeeen mmmmp εε Δ⋅∝Δ⋅=⎟⎠⎞

⎜⎝⎛ Δ⋅⋅=

Δ⋅=

Δ −5222

10v22

v2

Increase of the kinetic energy of a neutral species of the mass (m)

mmmm ⎠⎝ 222

22

3 eeeeee EneP)TT(kmm ν⋅⋅Δ ( )

2223 effee

eeeabseB

eee

eT

eee E

mneP)TT(k

mmn

mmn ⋅

ν+ω⋅ν

==−⋅⋅⋅ν⋅=εΔ⋅⋅ν⋅

T t diff (t t t d l)

)(~

)(~

)(3 22

2

22

2

222

22 EEk

EmeTT effeffeff

e

⋅⋅=−

Temperature difference (two temperature model)

)()()(3 21

222222 pcmk eeeBe ⋅+++⋅⋅⋅ ωνωνω


Non-thermal plasma

Transition from non-thermal to thermal plasmadue to pressure increase

105

104

Te

e (K

)

103

mpe

ratu

re

Non-thermalplasma!

10Tg

te

10-2 100 102 104 106 108102

pressure (Pa)


Why non-thermal plasmas ?Non-thermal plasma

Why non-thermal plasmas ?

● allows non-equilibrium processes for synthesis of novel materials q p ythin amorphous films/plasma polymerscomposite films containing nano-particles

● allows treatment of sensitive materials (e.g. polymers, living human and animal tissues !)

● enables processes which are not possible with conventional thermo-chemistry or would require a much higher effort

● in general good environmental compatibility due to low material turnover

Non-thermal low-pressure plasmas (rf discharge, glow discharge) Non-thermal atmospheric pressure plasmas (DBD, Corona)p p p ( , )


Gas discharges plasma so rces

Non-thermal plasma

Gas discharges - plasma sourcesTownsend discharge Barrier discharge (DBD)g

Glow dischargeArc discharge

g ( )Corona dischargeSpark discharge

Townsend-Mechanism Microdischarges, streamers

Radio frequency plasma (CCP/ICP, single/dual frequency)Microwave plasma / surface wave

Electrons in high-frequency electric field

M ti d lMagnetised plasmaMagnetron, Microwave - ECR, RF- Helicon

C l t ti E B d ift h ti

20

Cyclotron motion, ExB-drift, wave heating, resonances


Experiment, Diagnostics Modelling, SimulationNon-thermal plasma

Plasma plasma sheath

Experiment, Diagnostics Modelling, Simulation

Plasma, plasma sheath

● Microwave interferometry, probes● Spectroscopy (VUV vis IR)

● Kinetic modellingBMGL (electrons) PIC MC● Spectroscopy (VUV, vis, IR)

Emission, absorption, laser● Mass spectrometry

BMGL (electrons), PIC-MC● Fluid models (heavy species)● Hybrid models

Ions (energy resolved), neutralsThreshold-, attachment-MS

● Global models, macroscopic kinetics,reactor parameter, YASUDA-parameter

Interface, thin film

● In situ: ellipsometry, FTIR, ● Adsorption models, MC (TRIM)microgravimetry, …

● Ex situ: surface analysis(XPS XRD SIMS AFM SEM )

Species fluence, sticking coefficients Chemical sputtering, …MD Si l ti(XPS, XRD, SIMS, AFM, SEM, ...) ● MD-Simulations


Kinetics of non-equilibrium plasmasNon-thermal plasma

BOLTZMANN equation – single particle distribution function fi

( ) ( )[ ] )(iffFffdf

∑ ∫∫⎟⎞

⎜⎛ ∂∂∂∂

rr ( ) ( )[ ] )(

, klmni

klmnklnmklmnkll

coll

ii

i

ii

ii ffffddtff

mF

rf

tf

dtdf

vvvvv

v ∑ ∫∫∋

−⋅⋅−⋅Ω=⎟⎠⎞

⎜⎝⎛

∂∂

=∂∂

⋅+∂∂

⋅+∂∂

= ϑσrrr

integral operatordifferential operator integral operatorcollision term velocity variation, due to collisions, generation/destruction of particles

differential operatorflow term particle movement in phase space

generation/destruction of particles

external electric and magnetic fields, macroscopic space charge field

micro fields and quantum physics of atomic or molecular interactions

binary collisions

at short distances

y

Ak + Bl → Cm + Dn

σklmn

k l m nΔEklmn


Macroscopic: particle balance equation – rate coefficientNon-thermal plasma

iiii LSjdiv

tn

−=+∂∂

k

NNNNAB

k ≠ k !Elementary processes

t∂

DCk

BA NNNNCD

++ ↔ kAB ≠ kCD !Elementary processesChemical reactions

∫ ⋅⋅⋅=⋅= ABABABABABABAB d)f(σσk vvvv

Rate coefficient:

∫ ABABABABABABAB )f(

e.g. production of charged particles by electron impact (source term)

vσnnknnνndne ⋅⋅⋅=⋅⋅=⋅=⎥⎤

⎢⎡

e + Ar Ar+ + 2e

vσnnknnνndt ioneArioneArione

ion

⋅⋅⋅=⋅⋅=⋅=⎥⎦⎢⎣2nd Graduate Summer Institute Complex Plasmas, August 5 – 13, 2010, Greifswald, Germany 23

Elementary processes in plasma / gas phase

Non-thermal plasma

• generation of charged and neutral reactive species due toi l ti l t t l lli i

Elementary processes in plasma / gas phase

inelastic electron – neutral collisionse + O2 O+ + O + 2ee + CF4 CF3

+ + F + 2ee + CF4 CF3 + F-

• ion – molecule reactionsO2

+fast + O2 therm O2 fast + O2

+therm

H2+ + H2 H3

+ + H

• radical – radical reactionsCF + F2 CF2 + F

Plasma chemical gas conversionformation of new stable gas moleculesMacroscopic formation of new stable gas molecules formation of nano- and micro-particles

p

17

Non-thermal plasma

Example: non-thermal oxygen plasma

Reactions between plasma species:

O, O2, O3

O+, O2+, O3

+

O- O - O - more than O , O2 , O3

O2 (a1Δ), …

100 elementary reactions !

2 ( ),

electrons

18

l t ith l t

Non-thermal plasma

some elementary processes with electrons

19

S l t ith t l d i

Non-thermal plasma

Some elementary processes with neutrals and ions

......

22

Outline






● Outlook

28

Out oo


Plasma sheathPlasma boundary

t ti l h th

Assumptions

● stationary plasma sheath

● no collisions

● completely absorbing surface

● MAXWELLian electrons

● single charged positive ions

● kBTe = 2…3 eV >> kBT+

● BOHM criterion:

bohmeBbohm eTkm ϕΔ⋅=⋅⋅=⋅+

21

22v

Surface on floating potential:

⎟⎞

⎜⎛⋅ mTk1 ⋅TkB

bohmeBbohm ϕ22

29

⎟⎟⎠

⎞⎜⎜⎝

⎛⋅⋅

⋅⋅=Δ+Δ=− +

e

eBSheathBohmspl m

meTk 43.0ln

21ϕϕϕϕ ~10...15 V

++ ⋅⋅⋅=

mTknesj eB

pl61.0)(


High voltage plasma sheath eΔϕ>>k T

Plasma boundary

Powered electrode in rf plasma (ccp)

High-voltage plasma sheath, eΔϕ>>kBTe

31

λ+<<s no collisions

2max

232

1

00

2v

sme

Cnej sbohm

ϕε ⋅⎟⎟⎠

⎞⎜⎜⎝

⎛ ⋅⋅⋅=⋅⋅=

+++

5

212

321

00

268.1v

enej s

bohm+

+⋅

⋅⎟⎟⎞

⎜⎜⎛ ⋅

⋅⋅≈⋅⋅=λϕε

λ+≥s transition regime

25

max

00sm

j bohm+

+ ⎟⎠

⎜⎝

M A Lieberman and A J LichtenbergPrinciples of Plasma Discharges and Material Processingcollisionsλ+< s Principles of Plasma Discharges and Material ProcessingJohn Wiley & Sons, Inc, Hoboken, NJ, 2005

3

2

000 8

9vcoll

sbohm sp

bnej ϕε ⋅⋅⋅≈⋅⋅= ++

+


Ion energy distribution at rf discharge electrodesPlasma boundary

ϕ=0

S AsymmetricIon energy distribution

PLASMA Asymmetricrf plasma

13.56 MHz

powered electrode grounded electrode

Ar+Ar+ 5 Pa 5 Pa

ϕRF [cps

]

[cps

]

Inte

nsity

[

Inte

nsity

[

Ion Energy [eV] Ion Energy [eV]

Capacitive rf sheathM Zeuner, H Neumann and J MeichsnerJ. Appl. Phys. 81(1997)2985


Plasma boundary

ω25.0==Θ +

ωω p

10==D

ex

λλλ

Dλ

20⋅

Φ rfUe20=

⋅=Φ

eB

rfrf Tk

Overlappingsattle-shaped structure charge exchange collisionscharge exchange collisions

32

Outline






● Outlook

33

Out oo


Plasma diagnosticsOxygen rf plasma

g

ProbeProbe, MW interferometry,MSOES TALIFOES, TALIF

13.56 MHz

Capacitively coupled unconfined rf plasma (CCP)


Oxygen rf plasma

Plasma density (Langmuir-probe)

p = 5 Pa, Upp = 800 V

hE: distance to thepowered electrode

ath

109 1010 cm-3

sma

she 10 …10 cm

rf pl

as

J. Meichsner et al., Surf. Coat. Technologie 98, (1998), 1565 - 1571

35

160 GHz Microwave interferometry, GAUSSian optics

Oxygen rf plasma

y, p

Line integrated electron density

Talk: C. KülligPoster

Electron densityInstabilities


Poster Negative oxygen ions

Mass spectrometry - ion analysis: oxygen rf plasma

Oxygen rf plasma

13,56 MHz

Mass spectrometry ion analysis: oxygen rf plasma

Monochromator RF-PlasmaO*

CCPasymm.

ICCDRF-Plasma

HIDEN EQP 300Ion analysis

O + O+HIDEN EQP 3001 – 300 amu1 – 1000 eV

O2+ O+

O2- O-


Energetic positive ions at the powered rf electrodeOxygen rf plasma

1000 Vpp5 Pa

g p p13.56 MHz plasma (CCP) in oxygen

O2+ 1000 Vpp

25 Pa

50 Pa1000 Vpp

800 Vpp

O2

15 Pa

10 Pa

pp

600 Vpp

400 Vpp

1000 VO+5 Pa 1000 Vpp

50 Pa

1000 Vpp

800 Vpp

O+

25 Pa

15 Pa10 Pa

800 Vpp

600 Vpp

400 V400 Vpp


Energetic negative ions at the grounded electrodeOxygen rf plasma

IEDF shifted by 2000 cpsIEDF hift d b 2000

g g g13.56 MHz plasma (CCP) in oxygen

IEDF shifted by 2000 cps IEDF shifted by 2000 cps

O-O-

y [c

ps]

y [c

ps]

Inte

nsity

Inte

nsity

p = 7 PaQ

USB = 800 VQ

Ion energy [eV]Ion energy [eV]

Q = 2 sccmd = 2 cm

Q = 2 sccmd = 2.5 cm

Ion energy [eV]Ion energy [eV]


Ground state atomic oxygen density

Oxygen rf plasma

Ground state atomic oxygen density

Two photon absorption laser induced fluorescence - TALIF

13 3

dzUp 2

b ⋅⋅ similarityAxial O-density distribution

3·1013 cm-3

0,8

1,0

nsity

0 4

0,6

orm

. O-d

en

d = 25 90 mm

0 100 200 300 400 00 600 00

0,2

0,4no

USB= -350 V

d = 25 ... 90 mmp = 20 ... 100 PaUSB = 100 ... 500 V

S. Peters et alC t ib Pl Ph 45 N 5 6 373 (2005)

0 100 200 300 400 500 600 700 pz2Ub/ d (mm V Pa)powered grounded

Contrib. Plasma Phys. 45, No. 5-6, 373 (2005)


VUV plasma radiationOxygen rf plasma

Breaking of chemical bonds in organic materials by energetic photons, λ< 200 nm, and initiation of radical reactions.

13.56 MHz plasma, CCP

H2

H2Ueff=150 V, p= 15 Pa, Q= 5 sccm121.5 nm

(Lyman α)

H2 continuum

2

N2

N2

O2

O2

Ar

2

ArUeff=150 V, Q= 5 sccm

130 nm (O 3P-3S0)

I t l i i i t it

eff

S t l di t ib ti f i i i t it Integral emission intensity(115 nm – 160 nm)

Spectral distribution of emission intensityfor different gases


Emission spectrum rf oxygen plasma (CCP)

Oxygen rf plasma

O3 5P

p yg p ( )

Atmospheric band

O+ O2

3p 5P1,2,3

777,4 nm]

Atmospheric band760 nm

3s 5S

sity

[a.u

.

O2+

3p 3P1,2,0Inte

n

O

3s 3S

844,6 nm

3s S

Wave length [nm}


Space and time resolved optical emission spectroscopy

Oxygen rf plasma

Space and time resolved optical emission spectroscopy

Monochromator RF-PlasmaO* 13,56 MHz

CCPICCDRF-Plasma CCP

asymm.

axial resolution < 1 mmspectral resolution < 0,1 nmtemporal resolution < 2 ns

Ion analysisO2

+ O+

O2- O-

Monochromator:0,5 m3 grids g = 600, 1200 & 1800

2ICCD-Kamera(PI-MAX, Gen II RB) 512 x 512 PixelQuantum efficiency:≈ 2% (800nm) 15% (500nm)

HIDEN EQP 3001 – 300 amu

≈ 2% (800nm).......15% (500nm) 1 – 1000 eV


Oxygen rf plasma

74 pictures

74 measurements

p

ObjectiveICCD-camera


Sheath dynamics – excitation patterns Oxygen rf plasma

rf sheath heating

secondary electrons

heavy particle excitationI rf sheath heatingII secondary electrons

III field reversal IV heavy particle excitation

tage

[V]

elec

trode

f-bia

s-vo

lt

Dis

t. rf

e

Time [ns] Time [ns]

Sel

Pressure [Pa]

S. Nemschokmichal,IEEE, 2008


Oxygen rf plasma

Increasing total pressure

Increasing modulationof the excitation ratefor heavy speciesexcitation:excitation:

ion flux modulation

Transitionα γ mode


PIC MCC Si l ti

Oxygen rf plasma

dx vdt

=r

r

PIC-MCC Simulation

( )dv q E v Bdt m

= + ×r r rr

( )1E

x

ϕ

ϕ ρ

= −∇

Δ = −

rΔt

( )0

ϕ ρε

E

⎧⎛ ⎞⎛ ⎞

E

( )ii

i

q S x xx y

ρ = −Δ Δ

∑

( )1 1

0

x yx yS x x x and y y

⎧⎛ ⎞⎛ ⎞− −⎪⎜ ⎟⎜ ⎟Δ Δ= ≤ Δ ≤ Δ⎝ ⎠⎝ ⎠⎨⎪⎩

EE

K. Matyasch, D. Tskhakaya, R. Schneider


Oxygen rf plasma Included elementary processes

PIC-MC simulation+Experiment

3 paper series:F X B ld K Ditt D D dF.X. Bronold, K Dittmann, D Drozdov, H Fehske, B Krames, K Matyash, J Meichsner, R Schneider, D TskhakayaJ. Phys. D. Appl. Phys., 40(2007),6583 -6607

K. Dittmann, K. MatyashS. Nemschokmichal, J. Meichsner, and R. SchneiderC t ib Pl Ph 2010 t dContrib. Plasma Phys, 2010, accepted


Experiment PIC-MC SimulationPhase-resolved OES

Oxygen rf plasma

Ti d OESTime-averaged OES


Ion energy distribution O2+ at the powered electrode

Oxygen rf plasma

Ion energy distribution O2 at the powered electrodePIC-MC simulation

Experimentp


Plasma modification of polymer surfacesOxygen rf plasma

In situ FTIR spectroscopy

Plasma modification of polymer surfaces

Polyethylene - PE

a.u.

In situ FTIR spectroscopy

- CH2 -bsor

banc

e a

rmal

ized

ab

no


In situ FTIR-ATR (Attenuated Total Reflection)Oxygen rf plasma

( )

Principle of the measurementPlasma processing chamber

Plasma

RF

● 45° ATR-Element IRG 100 (Ge-Sb-Se glass)

● Number of reflections: 34 , in the sample region 13

● Effective thickness of the sample: deff ~1,9 dProbe

Effi i i i ith t i i i t 25

N J HarrickInternal Reflection Spectroscopy,Interscience, New York, 1975]

● Efficiency in comparison with transmission experiment: 25


Interaction O2-plasma – polyethylene (PE)Oxygen rf plasma

in situ FTIR (ATR) analysisa.

u.

ratio spectra

Polyethylene - PE

- CH2 -bsor

banc

e

CH2

orm

aliz

ed a

no

Oxygen

C=O formation CH2 loss


Thin plasma modified surface layerOxygen rf plasma

TRIM SimulationOxygen ions PE Spectroscopic ellipsometry

epth

[nm

]

n P

E 100 eV O2+

Polyethylene – O2 plasma30 W, 30 Pa, 10 s

x

enet

ratio

n de

strib

utio

n i

300 eVO+

Modified surface layer, d=3 nm

ctiv

e in

dex

Ion energy [eV]

P

Rel

. O d

is Unmodified PE, d=15 nm

Ref

rac

Depth [nm] Wavelength [nm]

In steady state: etching and surface modification (oxydation) take place simultaneously !etching and surface modification (oxydation) take place simultaneously !


Characteristic penetration depth of species in polymersOxygen rf plasma

Plasma species Energy Interaction Depth

Ions,Fast neutrals

102 - 103 eV Elastic collisions,sputtering, chemical

2-5 nm

reactions...10 eV... Adsorbate sputtering,

chemical reactionsTop monolayer

Electrons (!) 5 -10 eV Inelastic collisions,Dissociation/ionisation on the surface

...1 nm ...

Reactive neutrals:- atoms, - molecules

thermal Energy,0,05 eV

Adsorption, chemicalsurface reactions,Formation of functionalgroups production of low

Top monolayer

groups, production of lowmolecular (volatile) compoundsDiffusion and chemical VolumeDiffusion and chemical reactions

Volume

Photons > 5 eV (VUV)

Photochemical reactions ... 10 - 50 nm ...( )

< 5 eV (UV) Secondary processes µm-scale


Influence of polyethylene treatment on plasma compositionOxygen rf plasma

Difference neutral mass spectraat the grounded electrode

PEd = 4 cmp = 5 Pa

Difference ion mass spectraat the grounded electrode

PE on

y y

PE ongrounded electrode

H2OCO

CO2

p 5 PaUpp= 800 V

sity

[cps

]

PE ongrounded electrode

H3O+

CO+ CO +ity [c

ps]

Inte

ns

CO CO2+

Inte

nsi

Mass [u]

PECO

Mass [u]

PE onpowered electrode

H2O CO

CO2

ty [c

ps]

PE onpowered electrodeH3O+

CO+CO2

+

y [c

ps]

Inte

nsit

Inte

nsity

Mass [u]Mass [u]562nd Graduate Summer Institute Complex Plasmas, August 5 – 13, 2010, Greifswald, Germany

Outline




● Example oxygen ccp rf plasma


● Outlook

57

Out oo


Fluorocarbon rf plasma

Transient species Stable reaction products

Ions

Plasma sheathPrecursors

Oligomers

a‐C:F thin film

S b t t / ll

Precursors

Substrate/wall


Fluorocarbon plasmas for etching/thin film deposition,Fluorocarbon rf plasma

p g p ,and surface modification

A Sanakaran P Subramonium

... Winters, d`Agostino,

A. Sanakaran, P SubramoniumU. of Illinois, 2003

, g ,Oehrlein, Kushner,Graves, Booth,Meichsner, …

Many activities over the last decades


Plasma chemical gas conversiont bl ti d t


re

stable gaseous reaction productscontamination of reactor walls

Deposited mass

mas

s

mas

s

pres

sur

ress

ure CF4

C3F8

pat reactor wall

m p

Deposited massat reactor wall

time time602nd Graduate Summer Institute Complex Plasmas, August 5 – 13, 2010, Greifswald, Germany

Silicon etching and film deposition, simultaneously


Etching Film deposition / passivation

Silicon etching and film deposition, simultaneously

ange In situ

microgravimetry

Mas

s ch

a microgravimetryΔm >1µg

M

H-U Poll, J MeichsnerThin Solid Films , 1985

Time

Polymer film thickness of between 1 nm to 5 nm



MgO-MaskMgO Mask

plasma polymer,side wall protectionSiO2

1 µmp2

CF4 C2F6 C3F8

anisotropy


Influence on the reaction kinetics due to hydrogen admixtureFluorocarbon rf plasma

CF4 + e CF CF2 CF3 ions C2F4, C2F6 , C3F8 , “Polymer”F F2

id preferredrapid preferred

H d i t [C/F]

e.g. H2 + F HF + H

H2 admixture [C/F]

g 2H + F2 HF + F CFx + H CFx-1 + HF

Reducing of fluorine due to production of HFIncreasing of CFx radical densitiesFormation of unsaturated and saturated fluorocarbons, film deposition


Transient species diagnostics – film deposition /etchingFluorocarbon rf plasma

Polarizer Analyzer

p g p g

Polarizer Analyzer

Elli t IR TDLASIR‐StrahlIR beam

Ellipsometry IR TDLASSi substrate

V

Process gasesMatching unit

Vacuum pump

RF electrode Process gases

RF generator


Infrared Tunable Diode Laser Absorption SpectroscopyFluorocarbon rf plasma

IR-TDLAS

radicals

stablemolecules

CF: 1308,5 cm-1 (2Π1/2 R7,5)CF : 1096 3433 cm-1 (P (21))

Spectral resolution: 10-3 cm-1

Temporal resolution 1 msCF2: 1096,3433 cm (P2(21))CF3: 1261,307 cm-1

CF4: 1250-1300 cm-1

C F 1180 1

Temporal resolution 1 ms

C2F4: at 1180 cm-1


State of reactor walls on CF2 kinetics in pulsed CF4 plasmaFluorocarbon rf plasma

50 Pa, 50 W, 10 sccm CF4

221 2 nknk

dtdn

−−=1

212)(

−

⎟⎟⎠

⎞⎜⎜⎝

⎛+=

ntktn 12

)( 020 += tnktn

n

4222 ?)( 2 FCWallCFCF k⎯→⎯++Wall with a-C:F layer:

second order reaction (k1 = 0)

dt 0 ⎠⎝ n )(tn

( 1 )


10 1.5 Thin film growth FC species in gas phase


5

10

1.0

1.5IIIII

(nm

)

I

rate

(nm

/s)

0

5

0 0

0.5

m th

ickn

ess

on /

Etc

hing

r

100 W50 Pa 33% CF0 30 60 90

0

-0.5

0.0Fil

Dep

ositi

o

33% CF467% H2no gas flow

0 30 60 90Time (s)

0 2 8 0x10-4

1.0x10-3

n (%

)

0.2

6.0x10-4

8.0x10

Con

cent

ratio

n

CF

entra

tion

(%)

0.1

2.0x10-4

4.0x10-4

C F

CF2

F 2 -, C

2F 4 - C

CF

- C

once

0 30 60 900.0 0.0

C2F4

CF


50 Pa, 50 W, 0.1Hz, 50% duty cycle, )

Thin film growth FC species in gas phase vs H2 admixtureFluorocarbon rf plasma

total Gas flow rate 10 sccmSchicht

3

4

5

ate

(nm

/min

)

Thin film

1

2

3

depo

sitio

n r

0 10 20 30 40 50

-1

0

Ave

rage

d

0.33 0x10-4

3.5x10-4

n (%

)

t = 2.5 sec

(%)Gasphase

0 10 20 30 40 50H2 (%)

Gas phase

0.2

2 0x10-4

2.5x10-4

3.0x10

Con

cent

ratio

n

ncen

tratio

n (

0.1

1 0 10-4

1.5x10-4

2.0x10

2- (C

2F 4-) C

CF-

Con

0 10 20 30 40 50

0.0 1.0x10 4

CF 2


Outline






● Outlook

69

Out oo


Ch ll Mi l

Outlook

Challenge: Microplasmas

● Small dimensionsScaling laws

● Role of boundaries

ne

(cm-3) ● Role of boundariesSurface charge &temperatureSecondary species

(cm )

νep

y pQuantum effects

● Discharge stabilityOperation modes

Coupling of surface and

K. Tachibana, Kyoto

Coupling of surface and volume processes,

chemical micro-reactors

Plasma boundary physics

Atmospheric pressure plasma chemical micro reactorsAtmospheric pressure plasma


S th f f ti l t i l

Outlook

Syntheses of new functional materials

Preparation of metal polymerPreparation of metal-polymer compositesPlasma processes and energeticPlasma processes and energetic ions for material modification

Nanostructuring of surfacesNanostructuring of surfaces


TR24, Project B13, University of Kiel

Ch ll Pl t di i

Outlook

Challenge: Plasma meets medicine

Plasmas for cleaning / sterilisation

Plasmas for biocompatible surfaces

e.g. coated implants with increased cell adhesion andanti-microbial properties

Thin plasmapolymer film with NH2 functional groups and metallic nanoparticles.

Plasmas for tissue treatment PLASMA MEDICINEPlasmas for tissue treatment PLASMA MEDICINE


Thank you for attention !y

K Dittmann S Nemschokmichal C Küllig B KramesK. Dittmann, S. Nemschokmichal, C. Küllig, B. Krames, S. Stepanov, O. Gabriel, K. Li, S. Peters, K. Matyasch, R. Schneider


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