Pulse low temperature plasma systems for the deposition of oxide thin films Z. Hubi č ka 1 , M. Č ada 1 , P. Virostko 1,2 , V. Stra ň ák 1 , Š. Kment 1 , J. Olejní č ek 1 , P. Adámek 1 , L. Jastrabík 1 , M. Tichý 2 , P. Jelínek 1 , I. Gregora 1 , P. Kudrna 2 , M. Č i č ina 1 , R. Hippler 3 , P. Kluso ň 4 , J. Krýsa 4 1 Institute of Physics, Academy of Sciences of the Czech Republic,v.v.i., Na Slovance 2, 182 21 Prague 8 2 Charles University in Prague, Faculty of Mathematics and Physics, V Holešovi č kách 2, 180 00 Prague 8, Czech Republic 3 Ernst Moritz Arndt Univ Greifswald, Inst Phys, D-17489 Greifswald, Germany 4 Institute of Chemical Technology, Technicka 5, 166 28 Prague 6, Czech Republic Summer school PPST, August, 20, 2008 Koszalin, Poland
Acknowledgments • Ministry of Education, Youth and Sports, Research plan MSM 0021620834 • Czech Science Foundation, grant 202/06/0776 • Grant Agency of the Academy of Sciences of the Czech Republic, grant KAN 101120701, KJB100100707 and KJB100100805 Summer school PPST, August, 20, 2008 Koszalin, Poland
LECTURE OUTLINE 1. Motivation of the research aiming at deposition of TiO 2 . 2. Low-pressure plasma sources used for deposition of TiO 2 . a) UHV single plasma-jet system. b) UHV double plasma-jet system. c) Surfatron plasma jet system. d) DC planar magnetron. 3. Atmospheric pressure plasma source – barrier torch discharge. 4. Samples of plasma diagnostics. 5. Measurements of the ion current flowing at the substrate. 6. Measurements of power deposited at the substrate by using thermocouple probe. 7. Conclusion and future prospects. Summer school PPST, August, 20, 2008 Koszalin, Poland
Motivation • The aim - preparation of hiearchical multicomponent structure (sensors, solar cells) • Low temperature deposition is sought • The information of photo-electrochemical properties of TiO 2 is one of the most important EXPECTED DESIGN OF Layer of ZnO - TCO layer MULTILAYERS STRUCTURES (Transparent Conducting Oxide) � Filter of UV radiation � Protective layer Monolayer of Au � Enhance of electron transport Thin film of M-phtalocyanine � Sensitivization of TiO 2 � Deposition – CVD Layer of photoactiveTiO 2 � Photoactive layer Nanoporous alumina - template Summer school PPST, August, 20, 2008 Koszalin, Poland 2
Motivation visible light O 2 - Recently, the modification of TiO 2 to render its sensitivity to Reduction e - cb visible-light became one of the most important goals to O 2 2.5 eV increase the utility of TiO 2 . H 2 O N 2p ↔ O 2p h + vb Oxidation Some approaches: OH TiO 2-x N x particle a) Transition metals doping (Fe, Ni, Zr) X thermal instability X increase of recombination centers The substitutional anionic doping of N → O b) Reduced form of TiO 2 X low electron mobility in the bulk c) Dye sensitization By mixing N 2p states with O 2p states the band- X low efficiency gap of the TiO 2-x N x film is reduced <2.5 eV d) Composite semiconductors X fast recombination TiO 2-x N x films have a visible-light wavelength response Summer school PPST, August, 20, 2008 R.Asahi et al., Science 293 (2001) 269 Koszalin, Poland 3
Low temperature plasma sources Barrier torch DC pulsed HC plasma jet DC pulsed planar magnetron RF HC pulsed dual plasma jet Multi-barrier torch MW surfatron Summer school PPST, August, 20, 2008 Koszalin, Poland
RF, RF modulated, DC and DC pulse plasma jet Summer school PPST, August, 20, 2008 Koszalin, Poland
Hollow cathode effect Summer school PPST, August, 20, 2008 Koszalin, Poland
In the case of DC hollow cathode discharge, the pressure region for the optimum development of hollow cathode effect is done by the relation: ⋅ ≤ ⋅ ≤ ⋅ ⋅ 1 50 Pa m p a Pa m This relation is valid for cylindrical hollow cathodes with the internal diameter a . This relation says that the mean free path of electrons inside the cathode has to be optimal relatively to the diameter a for the effective development of fast oscillating electrons. Summer school PPST, August, 20, 2008 Koszalin, Poland
System with cylindrical hollow cathode Summer school PPST, August, 20, 2008 Koszalin, Poland
RF hollow cathode effect C1 and C2 electrode can be covered by dielectric material Summer school PPST, August, 20, 2008 Koszalin, Poland
The RF hollow cathode plasma jet was used for PECVD of a- Si:H and for PVD of many types of thin films: - TiN deposition by sputtering of a Ti nozzle - stoichiometric Ge 3 N 4 thin films - CN x thin films - Cu 3 N thin films -Pb(Zr x Ti 1-x )O 3 ferroelectric thin films - Ba x Sr 1-x TiO 3 ferroelectric thin films DC and DC pulsed plasma jet with hollow cathode was used for: -TiO 2 thin films -ZnO thin films -Si:H, SiGe:H, GeC semiconductor thin films deposition -SiC semiconductor thin films Summer school PPST, August, 20, 2008 Koszalin, Poland
Dependence of pressure at the hollow cathode outlet on mass flow rate through the cathode with internal diameter 5 mm Summer school PPST, August, 20, 2008 Koszalin, Poland
• RF, modulated RF hollow cathode plasma jet (Ti hollow cathode) • DC and DC pulse hollow cathode plasma jet (Ti hollow cathode) ? = DC pulse hollow cathode plasma jet RF modulated hollow cathode plasma jet Summer school PPST, August, 20, 2008 Koszalin, Poland
Double DC Pulsed Hollow Cathode Plasma Jet System for deposition of TiO 2 and TiO 2 :N thin films P RF ≈ 3 W • Hollow cathode: titanium nozzle inner diameter d = 5 mm and length l = 30 mm. • Working gases [sccm]: Ar (80), O 2 (100) • Total pressure: in the range 2-5 Pa • pulsing frequency 2.5 kHz with 25% duty cycle • Distance: nozzle outlet to substrate -30 mm • Substrate : quartz, ITO (Indium-Tin Oxide) Summer school PPST, August, 20, 2008 Koszalin, Poland 5
Inside of the Reactor with Double pulsed DC plasma jet plasma jets magnet poles substrates � In order to achieve a high thickness homogenity a mask was situated between the supports, which were positioned on a movable bench, and hollow cathodes. � Grounded poles of static electromagnet were situated close to the nozzle outlet in order to provide a higher intensity and superior stability of the plasma stream in the reactor. Summer school PPST, August, 20, 2008 Koszalin, Poland 6
DC Hollow Cathode Dual Plasma Jet system cooled jet I substrate turning cooled jet II Summer school PPST, August, 20, 2008 Koszalin, Poland
Inside of the reactor with double pulsed DC plasma jet during TiO 2 and TiO 2 :N thin films deposition Summer school PPST, August, 20, 2008 Koszalin, Poland
XRD analysis of TiO 2 and TiO 2 :N films deposited by double pulsed DC plasma jet XRD – Paralel Beam Geometry ω = 1° � Only the anatase crystal structures were detected by XRD � The presence of nitrogen in the plasma influenced the grain size which was estimated from the Scherrer equation and was in the range of 42 nm (A) – 58 nm (C) 3 4.0x10 3 3.2x10 480 nm Intensity [a.u.] 3 2.4x10 (A) (B) 3 1.6x10 (C) (C) (B) 2 8.0x10 (A) Anatase 0.0 20 30 40 50 60 70 80 o ] 2 Θ [ Summer school PPST, August, 20, 2008 Koszalin, Poland 8
V. Stra ň ák, DIAGNOSTICS OF LOW-TEMPERATURE PLASMA FOR TECHNOLOGICAL APPLICATIONS, Doctoral Thesis, PRAGUE, JANUARY 2007 Surfatron based plasma discharge surfatron* - based on principle of microwave resonator working at frequency 2.45 GHz discharge burns in quartz tube inserted into resonator cavity * M. Moisan, J. Pelletier, Microwave excited plasmas, Elsevier, Amsterdam (1999). A. Ricard, Reactive Plasmas, Societe Francaise du Vide , Paris (1996).
Experimental setup - surfatron • surfatron body • surfatron body • stainless steel vacuum vessel • double-surface quartz tube • plastic flanges • stepper motor operated feed-throughs • quartz windows • movable table in 3 dimensions • VAT butterfly valve • probe holder • MKS baratron • plasma exiting the tube
V. Stra ň ák, DIAGNOSTICS OF LOW-TEMPERATURE PLASMA FOR TECHNOLOGICAL APPLICATIONS, Doctoral Thesis, PRAGUE, JANUARY 2007 Surfatron plasma jet TiO 2 deposition � SURFATRON - Sairem GMP03 KE/D (0-300W) � Chem. precursor: Titan (IV) tetraisopropoxide � Working gases: Ar,O 2 (500 sccm/2 sccm) � Overall pressure : 1kPa � Substrates: quartz discs, ITO glasses � Temperature of the substrate : 330 °C � Substrate - nozzle distance : 8 mm � Time of deposition : 10 – 60 min 21 W, 110 Pa 21 W, 500 Pa 21 W, 800 Pa 21 W, 1100 Pa 21 W, 1500 Pa Summer school PPST, August, 20, 2008 10 mm 10 mm 10 mm 10 mm 10 mm Koszalin, Poland 7
DC pulsed magnetron deposition of TiO x thin films V. Stra ň ák, Marion Quaas, H. Wulf, Z. Hubi č ka, S. Wrehde, M. Tichý, R. Hippler, Formation of TiOx films produced by high-power pulsed magnetron deposition, Journal of Physics D, (2008) Volume: 41 Issue: 5 Article Number: 055202 • effective deposition of thin TiO x films low-frequency pulsed discharge* – f = 250 Hz ( t active = 150 μ s, t OFF = 3.850 μ s) • discharge properties in peak: I peak ≈ 50 A ( P peak ≈ 25 kW, i peak ≈ 1 Acm -2 ) • average values of discharge: I av ≈ 600 mA, P av ≈ 400 W (continual dc source AE MDX) •
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