Plasma based modification of thin films and nanoparticles Johannes Berndt, GREMI,Orléans
What is a plasma? A plasma is a ionized quasineutral gas! + electron electrons Neon bottle Ne atom Ne ion: Ne +
What is a plasma? A plasma is a ionized quasineutral gas! λ D = ε 0 n k B 2 ee T e debye length λ D Neon bottle Gas Plasma Neutral atoms, electrons, ions
What is a low temperature plasma? Vacuum vessel Energy Electrical current High frequency fields Plasma Gas Microwaves
The low temperature plasma Low temperature plasmas are not fully ionized! Ionisation degree: 10-6 - 10-4 Atoms/Molecules Gas temperature: 20 C Ions Ion temperature : 20 C Electrons Electron temperature : 50.000 C Low temperature plasmas are sytems far away from thermodynamic equilibrium
Low temperature plasma: T Elektron >> T Ion > T Gas Electrons have enough energy to Ionize atoms Ar + e - Ar + 2 e - Excite atoms Ar + e - Ar* + e - Dissociate molecules H 2 + e - H + H + e - v = 3kT m
Low temperature plasma: T Elektron >> T Ion > T Gas Excite atoms Ar + e- Ar* + e- Threshold: 10 ev Electron energy distribution function f(u) f(u) du: gives the number of electrons in the energy intervall [u,u+du] v = 3kT m
Example: discharge in acetylene Electron impact disscociation H 2 + e +2H +e H 2 +e H + H +e Acetylene depletion Mass spectrometer signal / a.u. 1 0.1 H 2 concentration C2H2 0 100 200 300 400 t / s Creation of radicals and ions H CH H + H -
Example: discharge in acetylene Electron impact disscociation H 2 + e +2H +e H 2 +e H + H +e Acetylene depletion Mass spectrometer signal / a.u. 1 0.1 H 2 concentration C2H2 0 100 200 300 400 t / s Creation of radicals and ions H CH H + H - further reactions Counts / s 17500 15000 12500 10000 0 25 50 75 100 125 150 7500 5000 2500 0 H 2 + Ar + C 4 H 2 + C 6 H 4 + m/e Postive ion Mass spectrum C 8 H 4 + C 10 H 4 +
H 2 + e Electon induced reactions H CH H + + CH H C H + C 2 H 2 C 4 H 2 2 + Chemical reactions H C 6 H 5 C 6 H 2 H 4 Flux of ions and radicals Substrate Thin films Etching Functionalisation 8 π* σ* 30 incident beam 1 µm Partial electron yield (au) 6 4 2 0 plasma 30s untreated 280 290 300 310 320 Photon energy (ev)
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H 2 + e Electon induced reactions H CH H + + CH H C H + C 2 H 2 C 4 H 2 2 + Chemical reactions H C 6 H 5 C 6 H 2 H 4 Positive Ion acceleration Flux of ions and radicals sheath Substrate Positive Ion acceleration Thin films Etching Functionalisation 8 π* σ* 30 incident beam 1 µm Partial electron yield (au) 6 4 2 0 plasma 30s untreated 280 290 300 310 320 Photon energy (ev)
Classification of species emerging from a plasma «Chemical reactivity» «Kinetic reactivity» «1 +2» Neutral radicals with thermal Energies 20 mev: Positive noble gas ions with high kinetic energies: Positive reactive ions with high kinetic energy H, CH 3.. N,F,H Ar + Xe +,Ne +.. H +, CH +,..
Classification of species emerging from a plasma «Chemical reactivity» «Kinetic reactivity» «1 +2» Neutral radicals with thermal Energies 20 mev: Positive noble gas ions with high kinetic energies: Positive reactive ions with high kinetic energy H, CH.. N,F,H Ar + Xe +,Ne +.. H +, CH +,..
«Separation of chemical reactivity and kinetic reactivity» «Flowing afterglow techniques» Suraftron Gas Glas cylinder pump
«Separation of chemical reactivity and kinetic reactivity» «Flowing afterglow techniques» wave launcher Power Creation of reactive species in the plasma plasma length zone L plasma L Gas flow glass cylinder Transport of reactive species sample neutral radicals neutral radicals + ions reaction chamber
«Separation of chemical reactivity and kinetic reactivity» «Flowing afterglow techniques» Example: Nitrogen plasma wave launcher plasma plasma N 2 + e - N + + N + 2 e - Gas flow glass cylinder Suraftron Gas Glas cylinder pump
TIMS Flowing nitrogen afterglow 10000 N-->N + N 2 -->N + 2 -->N + +N plasma N 2 + e - N + + N + 2 e - 1000 wave launcher plasma Gas flow glass cylinder Counts/sec 100 10 I Background I Plasma ON I Plasma OFF Suraftron 1 10 15 20 25 30 35 40 45 50 Electron Energy (ev) 1. Threshold: Ionisation of N-atoms Gas N + e - N + +2 e - 14.5 ev Glas cylinder pump 2. Threshold: Dissociative Ionisation of N 2 N 2 + e - N + + N + 2 e - 24.5 ev
Flowing nitrogen afterglow 10000 N-->N + N 2 -->N + 2 -->N + +N 1000 wave launcher plasma plasma N 2 + e - N + + N + 2 e - Gas flow glass cylinder Counts/sec 100 10 I Background I Plasma ON I Plasma OFF 1 10 15 20 25 30 35 40 45 50 Electron Energy (ev) Suraftron 1. Threshold: Ionisation of N-atoms Gas N + e - N + +2 e - 14.5 ev 2. Threshold: Glas cylinder pump Dissociative Ionisation of N 2 N + N + N 2 N 2 (B 3 Π g,ν ν = 10,11,12) + Ν 2 N 2 + e - N + + N + 2 e - N 2 (B 3 Π g ) N 2 (A 3 Σ u,ν = 7) + hν 24.5 ev
Flowing nitrogen afterglow 10000 N-->N + N 2 -->N + 2 -->N + +N 1000 wave launcher plasma plasma N 2 + e - N + + N + 2 e - Gas flow glass cylinder Counts/sec 100 10 I Background I Plasma ON I Plasma OFF 1 10 15 20 25 30 35 40 45 50 Electron Energy (ev) Suraftron Energy influx released by nitrogen recombination 1. Threshold: at different substrate materials * Ionisation of N-atoms Gas Glas cylinder * H. Kersten, D. Rohde, J. Berndt, H. Deutsch, R. Hippler Thin Solid Films 377 (2000) 585-591 pump N + e - N + +2 e - 14.5 ev 2. Threshold: Dissociative Ionisation of N 2 N + N + N 2 N 2 (B 3 Π g,ν ν = 10,11,12) + Ν 2 N 2 + e - N + + N + 2 e - N 2 (B 3 Π g ) N 2 (A 3 Σ u,ν = 7) + hν 24.5 ev
Reversible resistivity change of thin silver films R Thin 20 nm silver film on glass substrat
Reversible resistivity change of thin silver films argon/nitrogen mixture target
Etching of thin Diamond like Carbon films
Etching of thin Diamond like Carbon films T ( C) 350 300 250 200 150 125 etch rate (nm/min.) 1.00 0.37 0.14 Carbon atoms removed per impinging N atom 1,9.10-4 C/N 0 at 130 C Ar-10 % N 2 total flow : 150 sccm power : 150 Watts d = 15 mm 1,4.10-3 C/N 0 at 300 C 0.05 18.56 20.88 23.20 25.52 27.84 30.16 1/T (10-3 K -1 ) argon/nitrogen mixture target Etch rate 12 nm / min. Etch rate in an pure argon plasma 2 nm / min
H 2 Surfatron 1 Expanding plasma Surfatron 2 Double plasma experiment Wafer Ar Synergistic effects MS CH 4 H 2 H-atom source Wafer expanding argon Plasma
H 2 Surfatron 1 Expanding plasma Surfatron 2 Double plasma experiment Wafer Synergistic effects MS 1 + 1 = 5 Ar CH 4 H 2 Wafer H-atom source expanding argon Plasma etch rate in nm / min 5 4 3 2 1 argon plasma + hydrogen plasma argon plasma + H 2 gas 0 6 7 8 9 10 11 12 13 position on wafer / cm hydrogen plasma
Production of thin Diamond like Carbon films target 8 10 22 C - atoms cm 3 bias 4 10 22 C - atoms cm 3
«Chemical reactivity» «Kinetic reactivity» «1 +2» Neutral radicals with thermal Energies 20 mev: Positive noble gas ions with high kinetic energies: Positive reactive ions with high kenetic energy N atoms H - atoms Ar + ions H +, CH +,.. etching of DLC films etching of DLC films deposition of DLC films Modification of silver films Synergistic effects
Example: discharge in acetylene Electron impact disscociation H 2 + e +2H +e H 2 +e H + H +e Acetylene depletion Mass spectrometer signal / a.u. 1 0.1 C2H2 0 100 200 300 400 t / s Creation of radicals and ions H further CH H + reactions H - Counts / s 17500 15000 12500 10000 7500 5000 2500 0 + H 2 + C 4 H 2 Ar + + C 6 H 4 + C 8 H 4 + C 10 H 4 0 25 50 75 100 125 150 m/e
Electron impact disscociation 1 H 2 + e +2H +e H 2 +e H + H +e Acetylene depletion Mass spectrometer signal / a.u. 0.1 C2H2 0 100 200 300 400 t / s Creation of radicals and ions H CH H + H - further reactions
- - - - - - - - - Wall - - - - - - - - - - - - - - Wall plasma levitating dust cloud Some aspects of reactive complex plasmas J. Berndt, E. Kovacevic, I. Stefanovic, J. Winter and L. Boufendi, invited review, Contributions in Plasma Physics 49, 107-133 (2009) number of elemental charges 800 400 0 Monte-Carlo-Simulation 0 20 40 60 80 t /µs
superhydrophobic surfaces «Self-cleaning surfaces»
From superhydrophopic to superhydrophilic Plasma treatment
Deposit of Nanoparticles Well-alligned carbon nanotubes as coating Synthesized by PECVD after in-situ deposition of catalysts by PLD Contact angle ( ) 180 160 140 120 100 80 60 40 20 0 lotus effect superhydrophilic 0 50 100 150 200 Treatment time (s) Contact angle ( ) 180 160 140 120 100 80 60 40 20 0 lotus effect superhydrofilic 0 5 10 15 20 25 30 Treatment time (s)
Deposit of Nanoparticles Well-alligned carbon nanotubes as coating Synthesized by PECVD after in-situ deposition of catalysts by PLD XPS spectrum XPS spectrum Intensity (counts/s) 6.0x10 3 4.0x10 3 2.0x10 3 0.0 O C 2min N 2 plasma untreated Intensity (counts- au) 3x10 6 2x10 6 1x10 6 0 O O C C 30s untreated 600 400 200 0 Binding Energy (ev) 600 500 400 300 200 100 0 Binding energy (ev)
Deposit of Nanoparticles Well-alligned carbon nanotubes as coating Synthesized by PECVD after in-situ deposition of catalysts by PLD NEXAFS spectrum NEXAFS spectrum Total electron yield (au) 3.0 π* σ* 2.5 30s 2.0 C=C N plasma 1.5 1.0 0.5 H untreated 0.0 280 290 300 310 Photon energy (ev) Total electron yield (au) 9 π* σ* C=C 6 30s Nplasma 3 untreated 0 280 290 300 310 Photon energy (ev)
From superhydrophilic to superhydrophopic Plasma treatment 0.20 0.15 ν(c-o) δ(ch) ν(c=o) a) untreated material ν(ch) ν(oh) superhydrophob superhydrophil absorbance (au) 0.10 0.05 0.00 ν(c-o) ν(c-o) δ(ch) δ(ch) ν(c=o) b) treatment c) EUV-treatment ν(ch) ν(oh) ν(ch) ν(oh) VUV irradiation in vacuum 1000 1500 2000 2500 3000 3500 wavelength (cm -1 )
Production of patterned surfaces Super hydrophob superhydrophil Super hydrophob superhydrophob super hydrophil 1cm Plasma
Summary Each Plasma surface modification process as e.g. thin film deposition etching functionalisation is governed by a great variety of different species neutral radicals postive ions negative ions nanoparticles which can be calssified according to their «kind of reactivity» chemical reactivity kinetic reactivity chemical reactivity and kinetic reactivity The combined interaction of all these species can lead to synergistic effects