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6.a.preparation of thin films
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6.a.preparation of thin films

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preparation of thin films

preparation of thin films

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  • 1. Preparation of thin films
    • Methods of Evaporation
    • a) Resistive heating : Melt or Flash evaporation
    • b) Electron gun heating
    • c) Sputtering
    • d) Chemical methods
    • e) Pulsed laser Deposition
    • f) Molecular beam Epitaxy
    • g) Ion beam sputtering
    • h) Cluster deposition technique
  • 2.
    • Deposition Process involves:
    • Transition of a solid or liquid to a vapour/gas ions /plasma state
    • Vapour to reach the substrate from the source
    • Condensation of the vapour onto the substrate
    • forming a film.
    • Parts of a Vacuum system :
    • Vacuum pumps
    • Pressure gauges
    • Source from which material is evaporated
    • Substrate on which film is formed
    • Thickness monitor
  • 3.
    • Why vacuum?
    • To increase the Mean free path of the particles
    • To avoid oxidation of the films in case of non-oxide materials
    • Production of Vacuum : Atm pr. = 760 Torr
    • Rotary pump ~ 10 -3 Torr minimum pr.
    • Diffusion pump ~ 10 –6 Torr minimum pr.
    • Measurement of Pressure
    • Thermocouple gauge ( Pirani gauge)
    • Ionization gauge (Hot cathode)
    • 3. Penning gauge (Cold cathode Ionization gauge)
  • 4.  
  • 5. Rotary pump Block diagram of a Thin film coating unit G1 G2 G3 G1, G2 - Pirani gauges G3 – Penning gauge (Bayard-Alpert) Diffusion pump LN 2 Trap Vacuum Chamber Air inlet Stator &Rotor Rotary pump
  • 6. Diffusion Pump Silicone oil , heater Nozzles, Cooling water Addition of LN2 Cold Trap 1.Condenses some molecules 2. Reduces backstreaming 3.Improves vacuum by lowering pressure from 10 -5 to 10 -6 torr
  • 7. High Vacuum Low Vacuum (after diffusion pump) (after rotary pump) Low Pressure guages
  • 8.
    • Deposition Monitoring
    • Quartz crystal Oscillator – Resonance frequency shifts as mass gets deposited on the AT-cut Quartz crystal
    • Optical monitors – reflectivity
    • Resistance monitor
    • Fizeau fringes – interferometry Tolansky method
    • Profilometer
    Source material : should posses high melting point and not react with the material under study. W - boats, filaments, Ta, Mo - boats, Al 2 O 3- crucibles For reactive materials, flash evaporation is used instead of thermal evaporation
  • 9. l d d 0 h Source Substrate Uniformity of Film thickness - limited to a small area