Optjmizatjon of magnetron sputuer-depositjon process of thin fjlm - - PowerPoint PPT Presentation
Optjmizatjon of magnetron sputuer-depositjon process of thin fjlm coatjngs on a moving cylindrical substrate PhD. Student Seminar 07/04/2016 Thomas LE COZ Supervisors : A. Lacoste M. Mantel A. Bes C. Vachey Outline Context Why do we
Supervisors :
Thomas LE COZ
→ Why do we want to coat wire ? → Scientjfjc issues
→ Main specifjcatjons of reactjve sputuering in an inverted cylindrical magnetron (ICM)
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→ Characterizatjon of the fjrst used commercial magnetron
→ Characterizatjon of the magnetron designed by the company
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Sizing the system for : → Fast roll-to-roll process → Uniform coatjngs → High quality coatjngs Consideratjons : → Geometry → Electric → Magnetjc → Thermal
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E Target Substrate Cathode Water cooling Substrate holder (anode) e- Ar Ar+ e- e- + Vsubstrate Vcathode Vplasma
Plasma bulk Cathode sheath Anodic sheath
Substrate Cathode V → Ionizatjon of argon atoms by surrounding electrons → Potentjal drop in the sheath accelerates the ions used to sputuer the target
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→ Plasma close to the target → High density (1010 – 1011 cm-3) → Low pressure (0.1 Pa) → Race tracks leading to non- homogeneous coatjngs
Repulsive wall Cathode / Target Anode / substrate
→ Conformal geometry → No loss of matuer on the walls
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Lindberg et al., « Reactjve depositjon of nitrides and oxides using a twin- cathode inverted cylindrical magnetron », Surface and Coatjngs Technology 133-134 (2000) 484-488.
Metalic mode Poisonned mode → Argon plasma → Nitrogen as reactjve gas → Titanium target → Formatjon of TiNx on target and substrate → Instability of the stoechiometric point
Stoechiometry (x=1)
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→ Sputuering yield depends on the material
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Target Water cooling Magnet (NdFeB) Substrate Insulator 5 cm 10 cm Cathode :
Substrate :
Gas inlet Pumping → Two isolated targets for RF sputuering – we use DC sputuering
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Sofu iron
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Unit : T
→ 4 rings of 30 magnets → heterogeneity of the magnetjc fjeld → two racetracks per target → consumptjon of the targets : 30 % → Necessity of homogeneous magnetjc fjeld
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→ Two ways to get a homogeneous magnetjc fjeld :
Unit : T Magnetjc fjeld intensity on the target surface
0.038 T
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→ Two ways to get a homogeneous magnetjc fjeld :
Unit : T Magnetjc fjeld intensity on the target surface
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→ Electron leakage leading to the creeping and breaking of the wire
Atoms Ions
6 12 18 24 30 36
VA = 0 V
Power (W) Species
Electrons
10 20 30 100 200 300 400
Ofg-axis positjon (cm) Substrate temperature (°C) Species contributjons to the heat load of the substrate
→ Substrate to repulsive potentjal
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→ Decrease of the substrate temperature → Modifjcatjon of the spatjal distributjon of the plasma
Schematjc of the depositjon chamber and pyrometric setup
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→ Plasma characterizatjon through Langmuir probe measurements. VA = 0 V VA = 30 V
Distributjon of the Langmuir characteristjcs within the magnetron Positjon along the cathode axis (cm) Probe potentjal (V) Current (mA) Positjon (cm) Probe potentjal (V) Current (mA)
→ Spatjal redistributjon of the plasma with the variatjons of the anode potentjal
Vf Vp Saturation ionique Ipb (mA) Vpb (V)
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→ More energetjc electrons when polarizing and electron density slightly superior → Betuer ionizatjon but spatjal redistributjon of the plasma
No data because of a lack of collected current
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C Ti Acier Acier Ti
VA = 0 V → Hysteresis shifued to higher nitrogen fmows → Grain size variatjon due to temperature → Difgusion of iron in the tjtanium coatjng
ASTAR pictures made by S. Grosso, SIMaP
VA = 0 V
EDX characterizatjon made by S. Grosso, SIMaP
VA = 30 V
1 2 3 4 5 6 200 400 600 800 1000 1200 1400 1600 Ti - N2↗ (30 V) Ti - N2↘ (30 V) Ti - N2↗ (0 V) Ti - N2↘ (0 V) Nitrogen fmow(sccm) Relatve intensity (a.u.)
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→ Depositjon rate ≈ 60 nm/min → Depositjon profjle is changed due to plasma redistributjon
Cible Substrat
Heart-shaped pulverizatjon
Distance : D Cible Substrat Distance : D’
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3 6 9 12 15 50 100 150 200 250 300 350
mTorr 500 W
5 10 20 50 100
Target voltage (V) Current density (mA/cm
2)
1000 W
Ji ∝ (VT)12
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2 4 6 8 10 12 50 100 150 200 250 LPM (mm) Pressure (mTorr)
→ JT α (VT)12 → Minimal turn-on pressure : 5 mTorr → Mean free path at 5 mTorr ≈ 25 mm = Distance cathode-target → Maximal operatjng power : 1000 W (by constructjon)
Alexandru Todoran, « Magnetron sputuering in inverted cylindrical confjguratjon : 3D depositoin on moving substrate », thèse 2014
1 2 3 4 5 6 225 230 235 240 245 250 255 260 265 270 N2↗ (30 V) Nitrogen fmow (sccm) Cathode potentjal (V) 07/04/2016
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1 2 3 1 3 2 → More collisions due to the increase of species density leading to faster thermalizatjon → 1 : under-stoechiometric → 2 : stoechiometric → 3 : over-stoechiometric
1 2 3 4 5 6 200 400 600 800 1000 1200 1400 1600 Ti - N2↗ (30 V) Ti - N2↘ (30 V) N - N2↗ (30 V) Relatjve intensity (a.u.)
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→ Necessity of homogeneous magnetjc fjeld → Control of the substrate temperature by polarizing auxiliary electrodes … → … which infmuences the plasma distributjon within the reactjon chamber → Low depositjon rate → Power input limited → Unstable conditjons for stoechiometric coatjngs
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Unit : G → Non homogeneity of the magnetjc fjeld close to the target.
Ofg-axis positjon (cm) Bz (G)
150
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0 0,8 1,8 4 5,5 9 10 11 13,5 17 19,5 21 22 24,5 25,5 28,2 29 30
Gas Gas Magnets
Racetracks Racetracks
5 10 15 20 20 40 60 80 100 120 140 160
0 V - 30 s Ofg-axis (cm) Substrate temperature (°C)
→ 5 racetracks → 6 electrons leakage zones → Target consumptjon: 36 %
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→Higher sputuering for higher current →Increase of the ionizatjon rate
Hysteresis curves for difgerent target currents
→ Hysteresis for low nitrogen fmows
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→ Mean depositjon rate : 100 nm/min against 60 nm/min in commercial cathode → Heterogeneous thickness → Polarizatjon infmuences spatjal plasma distributjon
Depositjon rate as a functjon of the positjon in the cathode
Commercial cathode Ugitech’s cathode
Ofg-axis positjon (cm)
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→ Oxygen contaminatjon → Gold yellow is TiN → Blue is TiNxOy
N / Ti O/Ti 0.2 0.4 0.6 0.8 1 1.2 Ugi1– coté Ugi1 - Bosse Ugi1– centre
Ratjo of nitrogen and oxygen concentratjons with respect to the colors on the wire Coated wire made in reactjve mode under 30 V of polarizatjon, 5 min statjc depositjon
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→ Necessity of homogeneous magnetjc fjeld → Control of the substrate temperature by polarizing auxiliary electrodes … → … which infmuences the plasma distributjon within the reactjon chamber → Depositjon rate greater than for the commercial cathode → Unknown limit of power input – grater than that for the commercial cathode → Unstable conditjons for stoechiometric coatjngs → Oxygen contaminatjon – Unknown origin
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→ Sizing of a coil → Study the infmuence of the diameter of the targets → Modeling of the sputuering process → Modeling of the gas dynamics → Find the origin of the oxygen contaminatjon → Ultjmately design a new optjmized magnetron