INDUCTIVELY COUPLED PLASMAS: ONE BIG PRESHEATH? Carole Maurice 1 , Jaap Feijen 1 , Mark Kushner 2 , Gerrit Kroesen 1 1 Eindhoven University of Technology 2 University of Illinois at Urbana-Champaign http://uigelz.ece.uiuc.edu/presentations.html 14/10/2002 GEC 2002 Minneapolis 1
AGENDA • Introduction • Reactor Geometry • Diagnostics • Experimental and Modeling: Ion Velocity Distributions • Conclusions 14/10/2002 GEC 2002 Minneapolis 2
INTRODUCTION • In Capacitively Coupled Plasmas: distinctive regions – Glow: small E-field, ions nearly at rest – Pre-sheath: acceleration of ions to Bohm velocity – Sheath: space charge region, large E-field • How about Inductively Coupled Plasmas? 14/10/2002 GEC 2002 Minneapolis 3
REACTOR • Pancake, spiral electrode • 30 cm diameter • 4 cm axial length • 13.56 MHz 14/10/2002 GEC 2002 Minneapolis 4
REACTOR quartz plate electrode spiral antenna plasma 14/10/2002 GEC 2002 Minneapolis 5
DIAGNOSTICS • Doppler shifted LIF for ion velocity in the plasma volume • Langmuir probe for plasma potential, ion density and electron density • Energy resolved mass spectrometry for ion energy distribution at electrode 14/10/2002 GEC 2002 Minneapolis 6
DOPPLER SHIFTED LIF •Measure ion transport in plasma •Argon LIF scheme v ∆ = ⋅ •Moving ion → Doppler shift f i f L tr c 4p’ 2 F 7/2 laser 611.493 nm 490 263 GHz fluorescence 460.96 nm 3d’ 2 G 9/2 metastable 4s’ 2 D 5/2 14/10/2002 GEC 2002 Minneapolis 7
Model: Hybrid Plasma Equipment Model (HPEM) • Monte Carlo Simulation for EEDs • Kinetically derived current in Maxwell’s Eq’s. • Ion & Neutral Continuity, Momentum, Energy • Ion Monte Carlo Simulation to obtain velocity distributions; energy/angle distributions to substrate. 14/10/2002 GEC 2002 Minneapolis 8
LANGMUIR PROBE ELECTRON DENSITY 12 1.0x10 Setup2 • Electron density is mid 11 8.0x10 5 mTorr 10 11 cm -3 . 50 mTorr -3 ) Off axis maxima at ionic density (cm 11 6.0x10 higher pressures 11 4.0x10 denotes transition to collisional plasma. 11 2.0x10 400 W 0.0 0 2 4 6 8 10 12 14 16 radius (cm) 14/10/2002 GEC 2002 Minneapolis 9
velocity (m/s) DOPLLER SHIFTED -6098-4878-3659-2439-1220 0 1220 2439 3659 4878 6098 -9 5x10 39.5 mm LIF 0 39 mm 38 mm 35 mm 30 mm • Ion velocity distribution is LIF signal (A) 25 mm a drifting Maxwellian. 20 mm 15 mm 5 mTorr, 400 W 10 mm 5 mm 2 mm signal x3 1 mm signal x3 -9 5x10 signal x3 0.5 mm 0 -10 -8 -6 -4 -2 0 2 4 6 8 10 frequency shift (GHz) 14/10/2002 GEC 2002 Minneapolis 10
AVERAGE ION VELOCITY AND PLASMA POTENTIAL 1 v i 4000 potential 0 • No low E-field region mean ion velocity (m/s) 2000 Ions are in continuous -1 potential (V) acceleration from metal electrode 0 quartz plate midplane to surfaces. -2 -2000 -3 5 mTorr, 400 W -4000 -4 40 30 20 10 0 distance to electrode (mm) 14/10/2002 GEC 2002 Minneapolis 11
AVERAGE ION VELOCITY (MODEL) • Average ion velocity tracks the electric potential with nearly continuous acceleration from midplane. 400 W 14/10/2002 GEC 2002 Minneapolis 12
ION ENERGY DISTRIBUTIONS (r=0) • Monotonic increase in IED with decreasing pressure reflects: • Increase in plasma potential Decrease in collisionality 400 W 14/10/2002 GEC 2002 Minneapolis 13
ION ENERGY DISTRIBUTIONS (r=0) (MODEL) 14/10/2002 GEC 2002 Minneapolis 14
ION ENERGY DISTRIBUTIONS (r=0) (MODEL) • Monotonic increase in IED with decreasing pressure is captured 400 W 14/10/2002 GEC 2002 Minneapolis 15
4 4 1x10 6x10 2 6x10 30 W 35 W 40 W 30 W input 35 W input 37 W input 4 5x10 2 5x10 4x10 4 2 4x10 Counts (cps) Counts (cps) Counts (cps) 4 3x10 2 3x10 4 2x10 2 2x10 4 1x10 1x10 2 0 0 0 0 10 20 0 10 20 0 10 20 Energy (eV) Energy (eV) Energy (eV) -4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24 6 3.2x10 6 6 2.4x 10 2 .2x10 6 3.0x10 6 6 2.8x10 45 W 6 50 W 2.2x 10 100 W 2 .0x10 45 W input 100 W input 50 W input 6 2.6x10 2.0x 10 6 4.0x 10 4 6 1 .8x10 2.4x10 6 1.8x 10 6 6 1 .6x10 6 2.2x10 6 1.6x 10 6 2.0x10 6 1 .4x10 Counts (cps) Counts (cps) Counts (cps) 6 6 1.8x10 1.4x 10 6 1 .2x10 1.6x10 6 6 1.2x 10 6 6 1.4x10 1 .0x10 6 4 1.0x 10 2.0x 10 6 1.2x10 5 8 .0x10 5 1.0x10 6 8.0x 10 5 5 6 .0x10 8.0x10 5 6.0x 10 5 6.0x10 5 4 .0x10 5 4.0x 10 5 4.0x10 5 2 .0x10 5 2.0x 10 5 2.0x10 0.0 0.0 0.0 0.0 0 10 20 0 10 20 0 10 20 Energy (eV) Energy (eV) Energy (eV) -4 - 2 0 2 4 6 8 10 12 14 16 18 20 22 24 0 10 20 0 10 20 6 300000 6 300 0 00 30000 2.0x10 2 .0x10 6 1.6x 10 6 6 200 W 300 W 1.8x10 1 .8x10 150 W 100 W inpu t 800 W input 200 W input 250000 250 0 00 25000 1.4x 10 6 1.6x10 6 1 .6x10 6 6 6 6 1.2x 10 1.4x10 1 .4x10 200000 200 0 00 20000 6 6 1.2x10 1 .2x10 6 1.0x 10 Counts (cps) Counts (cps) Counts (cps) 6 6 150000 150 0 00 15000 1.0x10 1 .0x10 5 8.0x 10 5 5 8.0x10 8 .0x10 5 6.0x 10 100000 100 0 00 10000 5 5 6.0x10 6 .0x10 5 4.0x 10 5 5 4.0x10 4 .0x10 50000 50 000 5000 5 2.0x 10 2.0x10 5 2 .0x10 5 0.0 0 0.0 0 0.0 0 0 10 20 0 10 20 0 10 20 Energy (eV) Energy (eV) Energy (eV) Black: Ar+ Argon, 50 mTorr, Power series, 0-25 eV 14/10/2002 GEC 2002 Minneapolis 16 Green: ArH+
0 10 20 30 0 10 20 30 0 10 20 30 6 3 2x10 4000 6x10 3 1x10 10 W 50 W 60 W 3 3500 1x10 46 W 7 W 37 W 3 absorbed : 7.2 W 5x10 absorb ed : 3 6.6 W 3 absorbed : 45.7 W 1x10 2x10 6 2x10 6 3000 3 1x10 + + + Ar Ar Ar 9x10 2 4x10 3 2500 2 8x10 Counts (cps) C ounts (cps) C ounts (cps) 2 7x10 6 2000 3 1x10 3x10 2 6x10 6 6 1x10 1x10 1500 2 5x10 3 2x10 2 4x10 1000 + 2 3x10 + ArH + ArH ArH 3 1x10 2 2x10 500 1x10 2 0 0 0 0 0 0 0 10 20 30 0 10 20 30 0 10 20 30 Energy (eV) Energy (eV) Energy (eV) 0 10 20 30 0 10 20 30 0 10 20 30 6 5 6 5 3x10 1.6x 10 2x10 2.4x 10 4 6.5x10 5 2.2x 10 80 W 100 W 130 W 6.0x10 4 5 1.4x 10 63 W 84 W 111 W 5 2.0x 10 absorbed : 63.2 W 4 absorb ed : 8 3.7 W absorbe d : 111.4 W 6 5.5x10 2x10 5 5 4 1.2x 10 1.8x 10 5.0x10 + + + Ar 4 6 Ar Ar 5 4.5x10 2x10 1.6x 10 5 1.0x 10 4 Counts (cps) 4.0x10 s (cps) s (cps) 5 1.4x 10 4 3.5x10 4 6 5 8.0x 10 1x10 1.2x 10 3.0x10 Count 4 Count 5 1.0x 10 1x10 6 4 4 2.5x10 6.0x 10 6 4 1x10 8.0x 10 4 2.0x10 4 4 4.0x 10 6.0x 10 + ArH 4 + + 1.5x10 ArH ArH 4 4.0x 10 4 1.0x10 4 2.0x 10 4 3 2.0x 10 5.0x10 0 0.0 0 0.0 0 0.0 0 10 20 30 0 10 20 30 0 10 20 30 Energy (eV) Energy (eV) Energy (eV) 0 10 20 30 0 10 20 30 0 10 20 30 6 5 2x10 1.6x10 5 4.0x 10 200 W 400 W 800 W 1.4x10 5 178 W 360 W 695 W 5 absorbed : 178 W absorbed : 360 W absorbed : 695 W 3.5x 10 6 6 2x10 2x10 5 1.2x10 5 3.0x 10 + + + Ar Ar 4 Ar 2.0x 10 5 1.0x10 5 Counts (cps) s (cps) s (cps) 2.5x 10 6 4 1x10 8.0x10 5 2.0x 10 Count Count 6 6 1x10 1x10 4 6.0x10 5 1.5x 10 4 4.0x10 5 1.0x 10 + + + ArH ArH ArH 2.0x10 4 4 5.0x 10 0 0.0 0 0.0 0 0.0 0 10 20 30 0 10 20 30 0 10 20 30 Energy (eV) Energy (eV) Energy (eV) Black: Ar+ 5 mTorr, argon plasma, power dependence 14/10/2002 GEC 2002 Minneapolis 17 Green: ArH+
CONCLUSIONS • Acceleration starts from center of plasma, in both (!) axial directions. • Ions gradually accelerate to Bohm speed. • There is no real glow, just one big, symmetric presheath. 14/10/2002 GEC 2002 Minneapolis 18
Acknowledgements • Netherlands Technology Foundation (STW) • Netherlands Organization for Scientific Research (NWO) • Center for Plasma Physics and Radiation Technology (CPS) • National Science Foundation (NSF) • Semiconductor Research Corp. (SRC) 14/10/2002 GEC 2002 Minneapolis 19
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