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DEPOSITION (PVD (THERMAL (Comparison between Vacuum Thermal Evaporation…

- - - - Growing Techniques
        
        Vapor-Phase Epitaxy (VPE)
        
        Atomic Layer Epitaxy (ALE)
        
        Liquid-Phase Epitaxy (LPE)
        
        Molecular Beam Epitaxy (MBE)
        
        Metalorganic Chemical Vapor Deposition (MOCVD)
      - 2 type of epitacy
        
        Homoepitaxy (substrate & film same kind)
        
        eg: Si-Si
        
        Heteroepitaxy (Substrate & film different kind)
        
        eg: GaAs / AlAs sapphire
      - MOLECULAR BEAM EPITAXY (MBE)
        
        Definition.
        
        A technique via the interaction for one or more molecular or atomic beams that occur on a surface of heated crystalline substrate.
        
        Operation
        
        Vacuum system consists in a stainless-steel growth chamber.
        
        Pumping system consists of ion pumps and cryogenic pump.
        
        Ultra high vacuum used to obtain sufficiently clear epilayer.
        
        Effusion Cell
        
        -Provide excellent flux stability
        -Collection of gas molecules moving in the same direction.
        -Oven contain materials to make the beam.
        -Then it connected to vacuum system through a hole.
        -Substrate the located with a line of sight to the oven aperture.
        
        Working Principle
        
        Epitaxial Growth
        
        Provide an angular distribution of an atom or molecule in a beam.
        
        Substrate is heated to a necessary temperature.
        
        Atom will free to move to bond when get correct position in the crystal lattice.
        
        MBE Process
        
        The term beam means the evaporated atom did not interact with each other even other vacuum chamber gases until they reach the wafer.
  - - - Definition: The technique is based on the heat produced by high energy
        electron beam bombardment on the material to be
        deposited.
      - Working Principle:
        
        iii) The crucible is act as the anode.
        
        ii) The emitted electrons are accelerated
        towards an anode by a high potential
        difference (kV).
        
        i) The electron beam is generated by an electron gun, by using the thermionic emission of electrons that produced by an incandescent filament (cathode).
        
        iv) A magnetic field is applied to bend the electron
        trajectory, so the electron gun can be placed at the below of the evaporation line.
        
        v) The electron beam heat the target material and the material vapor is deposited on the subtrate
      - Diagram:
    - - Definition
        
        Thermal Evaporation is one of the simplest of the Physical Vapor Deposition (PVD) techniques. Basically, material is heated in a vacuum chamber until its surface atoms have sufficient energy to leave the surface.
      - Working Principle
        
        • Process of causing the pressure in a “liquid-filled container” to be reduced below the vapor pressure of the liquid.
        
        • Causing the liquid to evaporate at a lower temperature than normal.
        
        • Uses thermal and ion-beam for evaporation of source materials.
        
        • Uses thermal and ion-beam for evaporation of source materials.
        
        • Bulk materials are either electrically heated or subjected to electron bombardment (electron-beam) to turn to vapors.
        
        • Vapors then condensed and deposited onto substrate.
      - Diagram
    - - Source Used
        
        PVD
        
        Pure Source material
        
        CVD
        
        Typically used mixed source material
      - Chemical Reaction
        
        PVD
        
        No chemical reaction process at substrate surface
        
        CVD
        
        Involves chemical reaction process at substrate surface
    - - Material
        
        vacuum
        
        Metals or Low melt materials
        
        Electron Beam
        
        Both metals and Dielectrics
      - Process
        
        Vacuum
        
        Uses resistive heating, laser heating or magnetic induction to elevate the temperature
        
        Electron Beam
        
        the electron beam is focused on the target material, which locally melats
      - Diagram
        
        Vacuum
        
        Electron Beam
      - Impurity
        
        vacuum
        
        High
        
        Electron Beam
        
        Low
  - - - how it works
        
        sputter deposition occurs when target is negative
        
        substrate and chamber make a very large
        electrode
      - physical process
        
        (when) frequencies less than about 50 kHz
        
        electrons and ions in plasma are mobile
        
        basically DC sputtering of both surfaces
        
        (when) frequencies above about 50 kHz
        
        ions (heavy) can no longer follow the switching
        
        electrons can neutralize posi0ve charge build up
      - RF sputtering Advantages
        
        Easier to keep plasma going under these
        conditions: can operate at lower Ar
        pressures (1-15 mTorr)
        
        Fewer gas collisions: more line of sight
        deposition
        
        Provide optimum coating uniformity, very flat
        target erosion with no racetrack
        
        No disappearing anode problems
    - - problems
        
        positve charge builds up on the cathode (target)
        
        the –ve charge of the target is neutralized by the argon ions
        
        Ar+ ions won’t be attracted to the target anymore
        
        We need 10^12 V DC to sputter insulators
      - alternative
        
        Use RF to avoid charge build up by alternating
        potential
      - Definition
        
        A target material to be used for coating is bombarded with ionized gas molecule causing atom to sputter of into the plasma with DC applied on the cathode.
    - - Working Principle
        
        Magnetic field confines & trap electron that emitted by the cathode.
        
        Increase the probability of ionized of sputtering gas by maintaining higher density of ions.
        
        electron or working gas attracted to the cathode then collide
        
        ejected atom can condense on the cooler substrate
        
        Process repeated until layer deposition of thin film occur
      - The 'Glow Discharge' plasma that increase ionization of AR to the region closest to the target plate
      - Advantages
        
        High Deposition Rate
        
        deep erosion of target
        
        greater versatility
        
        Thin Film result
        
        most thinnest
        
        most uniform
        
        most cost-effective film
        
        strong bonding between film and substrate
    - - Source of Power
        
        RF
        
        Alternating Current, 13.5 Mhz is applied.
        
        DC
        
        Direct current
        
        Magnetron
        
        RF or DC Sputtering
      - Target Material
        
        DC
        
        Conductive material
        
        RF
        
        Commonly used from dieletric materials
        
        Magnetron
        
        uses magnet to trap target material