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E344: Thin Film Technology and Vacuum Basic - Coggle Diagram

- - - - Demands:
        
        Semiconductors --- Products: like multi-thin film coaters. Applications: lithography and other industrial equipment
        
        Health care/Biotechnology --- Products: optical monitor and deposition equipment film deposition for medical equipment visible/ infrared film thickness thickness meter. Applications: spectroscopy systems spectrophotometers, Others
        
        Display panels --- Products: ITO transport conductive film equipment. Application: PDP organic EL displays, liquid crystal, display liquids, crystal projectors
        
        Digital consumer electronics --- Products: Digital cameras, smart phones, projectors, tables Applications: lenses, dichroic mirrors, pickup systems
        
        Automobiles --- Products: sensors disposition, equipment for mirrors Applications: Infrared sensors, functional mirrors and lamps, augmented reality
        
        Optical communications --- Products: DWDM filters, deposition equipment Applications: DWDM switches
        
        Virtual augmented reality --- Products: head-mounted displays. heads-up display
        
        Environment and energy --- Products: Deposition equipment for energy-saving reflective mirrors. Applications: solar panels, energy-efficient lights, environmental measuring and analysis units
    - - Bottom-up approach: At the atomic scale, building up materials and structures atom by atom. Done through deliberate manipulation of matter by certain chemical and/or physical process
      - Top-down approach: using larger materials to make nanoscale structures in precise patterns through grinding / lithography
      - We can group techniques involved into 2 categories
        ( Can also be grouped into: 1) liquid phase epitaxial (LPE) and 2) vapor phase epitaxial (VPE) )
        
        Physical vapor deposition (PVD) -- Evaporation methods: Thermal evaporation, electron-beam evaporation, molecular beam epitaxy, laser beam evaporation, Ion planting evaporation Sputtering methods: Direct current (DC) sputtering, Radio frequency (RF) sputtering, Magnetron sputtering
        
        Chemical vapor Deposition (CVD) --- Metal-organic (MOCVD), low pressure (LPCVD), Plasma enhanced (PECVD), Atomic layer deposition (ALD) Sol-gel technique: Chemical bath deposition. Electroplating technique: Electroless deposition
- - - - Fabricate electronic components/devices like semiconductor chips, flat panel TV, smartphones, cars, LED lights and solar panels
        
        Vacuum Technology is needed
      - Needs many thin film deposition methods like evaporation, sputtering, molecular beam epitaxy (MBE)
        
        Operates at vacuum environment
    - - A pump is attached to the chamber with the intention of removing enough gas molecules from the chamber to reach the targeted pressure
      - How to see if pump is effective
        
        Pumping speed (S), Unit: L/sec or m^3/sec
        
        Conductance (C), Unit: L/sec or m^3/sec
        
        Throughput, Unit: Torr x litres/sec
        
        Time to pump down, Unit: sec
    - - Molecule movement changes with the increment of vacuum levels
        
        Viscous Flow ( 760 Torr to 1X10^-1 Torr ). Known as turbulent or laminar flow
        
        Transition Flow ( 1X10^-1 Torr to 1X10^-3 Torr )
        
        Molecular Flow ( < 1X10^-3 Torr )
    - - Low Vacuum gauges
        
        Capacitance Diaphragm Gauges
        
        Measures pressure difference between 2 volumes ( known pressure and an unknow pressure pressure) by the deflection of a thin metal diaphragm separating them. Useful range: above 10^-2 Torr
        
        Pirani Gauge
        
        Uses a reference filament immersed in a fixed gas pressure while the measurement filament is exposed to system gas. Both are heated by current. Useful range: 10^-3 to 10 Torr
      - High to ultra high vacuum gauges
        
        Ionization gauge
        
        Energetic electrons ionized the residual gases. The positive ions are collected at an electrode and the current is converted to a pressure indication.
        HOT CATHODE ION GUAGES, Useful range: 10^-10 to 10^-3 Torr
      - Procedure
        
        Pump down procedure
        
        1) Start up, turn on pump and open fore-line valve
        
        2) Close Fore-line valve
        
        3) Open roughing valve
        
        4) Rough chamber ~ 100mT
        
        5) Close roughing valve
        
        6) Open Fore-line valve and turn on High vacuum pump
        
        7) Open high-vacuum valve
        
        Venting procedure
        
        1) Close all the valves
        
        ( Close high-vacuum and roughing valves if you want to keep high vacuum pump on)
        
        2) Open vent valve until it reaches atmospheric pressure
- - - - Once deposition starts, more mass will attach to the crystal, causing the vibration frequency to change
    - - Different metal has different mass factor
  - - - Surface perpendicular to evaporation source aren't coated
        
        Due to poor line of sight as parts are not "seen" from certain views
    - - Thin film growth over a feature
    - - AR = (Step height)/(Step width)
  - - - Called epitaxial film
    - - E.g. MOSFETs (MOS field-effect transistors), LEDs, solar cells and laser
    - - Called epitaxy or epitaxial growth
  - - - Liquid phase epitaxial (LPE)
      - Vapor Phase Epitaxial (VPE)
      - Molecular-beam epitaxy (MBE) - under PVD evaporation family
      - Metal-organic chemical vapor deposition (MOCVD) - under CVD family
    - - Reflection high-energy electron diffraction (RHEED)
        
        Provides info on surface structure and morphology of sample
      - RHHED intensity oscillates as a function of film thickness
        
        Each oscillation correspond to completion of each atomic layer growth
    - - Metal-organic CVD (MOCVD) specialized CVD process for deposition of critical semiconductor material
        
        Operate at lower temperature than conventional CVD
        
        Usually occurs from 300-800 degrees Celsius and pressure varies from <1 Torr to atmospheric pressure
        
        Use organometallic source gases. E.G. tri-methyl gallium 3(CH3)Ga
      - Atom of an element are bound to one more more carbon atoms of and organic hydro-carbon group
  - - - leakage current = high power consumption & experiences RC delay ( lower processing speed)
      - Solutions
        
        1) (reduce leakage current) - Make the channel thinner to have better gate controlled through FD-SOI, FinFET and GAA 3D architecture
        
        2) (Reduce leakage current) - Use high-k metal gate
        
        3) (reduce RC delay) - Use Cu/low-k material
    - - Issues
        
        As size of transistor shrinks, performance degrades, i.e. leakage current resulting in high power consumption and experiences RC delay.
      - Solutions
        
        (reduce leakage current) - make the channel thinner to have a better controlled through FD-SOI, FinFET and GAA 3D architecture
        
        (reduce leakage current) - Use high-k metal gate
  - - - Growing different compound semiconductors
      - within same compound semiconductors by varying its composition
      - Colour variation + conditions
        
        Red
        
        Wavelength: 610nm < x < 760nm
        
        Semiconductor materials: AIGaAs, GaAsP, AlGalnP, GaP
        
        Green
        
        Wavelength: 500nm < x < 570nm
        
        Semiconductor materials: InGaN, GaN, GaP, AlGalnP, AlGaP
        
        Blue
        
        Wavelength; 450nm < x < 570nm
        
        Semiconductor materials: InGaN, ZnSe
  - - - Choice of material dictates band gap and operational wavelength
- - - - Sputtering & Evaporation are PVD as the thin film deposition that happen due to physical reaction
      - How does PVD work:
        
        Material to be deposited in vapour form by physical means
        
        Transported in low pressure from source to substrate
        
        Condensation on substrate to form thin film
    - - 4th state of matter -ionised gas
      - Contains free electrons (light) and +ve ions (heavy)
      - No neutral inside plasma if 100% ionized
      - Unstable
        
        At low temp, ions & electrons recombine into bond state causing the plasma back to gas (neutrals)
    - - Hot Plasma occurs in areas with higher temp ranging above 10^7 and number density ranging from 10^15 to above 10^33
      - Thermal Plasma occurs in areas with higher temp ranging from 10^4 to 10^7 and number of densities around 10^10 to 10^27
      - Cold Plasma occurs in areas with lower temp ranging from 10^2 to 10^5 and number density being 10^5 to 10^19
    - - ni^2 = 2.4 X 10^2 X nn X T^3/2 X e^-Ui/KbT
        
        ni = density of ionized atoms
        
        nn = density of neutral atoms
        
        Ui = ionization energy
        
        K = Boltzmann's constant
        (1.380649 × 10-23 m2 kg s-2 K-1)
        
        T = temperature
      - Ionization rate = ni / ( nn + ni )
        
        ne = electron density
        
        ni = ion density
        
        no = neutral density
      - What happens to density of ionized atoms (ni) when temp increases? Is plasma density now higher or lower?
        
        Solution: Density of ionized atoms (ni) increases when the temp increase. Plasma density is now higher
    - - Reactions (ion; A^+, electron: e^-, Excited states of atom: A^+)
        
        Ionization A2 + e^- = A2^+ + 2e^-
        
        Dissociative ion: A2 + e^- = A^+A + 2e^-
        
        Attachment: A2 + e^- = A2^-
        
        Detachment: A2^- + e^- = A2 + 2e^-
        
        Dissociation: A2 + e^- = A2
        
        Recombination: A2^+ + e^- = A2
        
        Atom recombination 2A^* = A2
      - Energy is needed to sustain plasma due to loss of charged particles by the reactions:
        
        Recombination ( between ion & electron )
        
        Diffusion ( of ion & electron from high concentration to low concentration)
        
        Convection ( flow of charges)
      - When it undergoes recombination, light is emitted which is called luminescence of plasma
    - - Precondition for the direct current (DC) plasma is to have Conductive Target
        
        Prevent from the charge build up and sustain the electric field
      - Voltage Distribution
        
        DC plasma structure:
        
        Two sheath: Anode (+) and Cathode (-)
        
        Different sheath potentials at the 2 electrodes
        
        If there's no plasma:
        
        Uniform dielectric materials in between the Anode and Cathode will allow the electric potential to drop with constant slope (uniform electric field)
        
        Plasma region; highly conductive
        
        Sheath region: less conductive
        
        Net effect of +ve charges in plasma makes the potential higher than anode
        
        high electric field in cathode region is favourable for ion bombardment
    - - one-third of IC fabrication steps are typically Plasma-based
      - Different types of gas are used depending on the application
        
        Argon (gas discharge) => Sputter-deposit (Action) => Aluminium / tungsten (Add / remove materials)
        
        Oxygen (gas discharge) => Sputter-deposit (Action) => high-temperature superconducting films (Add/ remove materials)
        
        iH2Cl2/NH3 (gas discharge) => PECVD (Action) => Si3N4 (Add / remove materials)
        
        BF3 (gas discharge) => Implant (Action) => Implant B into Silicon films (Add / remove materials)
        
        CF4/Cl2/O2 (Gas discharge) => Etch (Action) => Selectively remove silicon films (Add / remove materials)
        
        Oxygen (gas discharge) => Remove (Action) => Photoresist or polymer films (Add / remove materials)
      - Examples
        
        Lighting
        
        Spray coatings
        
        displays
        
        materials processing
  - - - Avoid interfering with those used for short wave radio communication e.g. taxis, police cars, aircraft
        
        US federal communications committee declared the 13.56MHz and 2.45 GHz frequencies are set aside for plasma generation
      - 13.56MHz
        
        CCP - capacitive coupled plasma (plasma between 2 parallel plates)
        
        ICP - Inductive coupled plasma (Plasma induced by surrounding coils)
        
        Low ionization rate FRF << Fcollision
    - - 2.45GHz
        
        Has high freq electromagnetic gas discharge
        
        High ionization rate FRF approximately Fcollision (at which resonance can be expected to enhance ionization)
        
        Allows to spatially separate the location of plasma generation from location of surface processing
- - - - RF peak to peak voltage is 1KV, electron densities are 10^9 to 10^11 Cm^-3 and chamber pressure is 05 to 10 mTorr
      - RF power is suitable for all the materials but most commonly used for depositing films from dielectric target materials
      - Deposition rate is low compared to DC sputtering
      - Used for smaller substrates sizes due to high cost factor of RF power supplies
      - Sputtering type (features) => magnetron only (DC sputtering) => magnetron or diode (RF Sputtering)
      - Target materials (features) => conductive only (DC Sputtering) => All the targets (RF Sputtering)
      - Sputtering rate (features) => 100% of DC (DC Sputtering) => 20% of DC, no magnetron (RF Sputtering)
      - Cost and complexity (features) => Best (DC Sputtering) => Very Good (RF Sputtering)
      - Campaign length i,e loss of anode (features) => Good (DC Sputtering) => Excellent (RF Sputtering)
  - - - For metal target, the DC bias is applied to anode and cathode
      - For insulating target, RF bias is applied instead.
  - - - e.g. TiN film deposition: Ti + (Ar, N2) => TiNx
  - - - DC / RF power
      - gas flow rate
      - substrate temperature
      - base / working pressure
      - types of gas
    - - e.g. a higher power leads to higher film deposition rate which gives rise to a higher film thickness
      - Film Deposition rate = (Film Thickness / Deposition duration)
  - - - Overhangs at contact openings
      - Thin deposition on sidewalls
      - 3.Discontinuities at contact bottoms
  - - - Ion incident angle
      - Energy of the ion
      - Masses of the ion (M1) and target (M2)
      - Surface binding energy of atoms in the target. (CA3 slide 30 for formula)
  - - - no: total no. of molecules
      - n: no. that suffered collision
      - d: source-to-substrate distance
      - λ: mean free path
      - e: exponential = 2.71828 (to 5d.p)
  - - - porous structure consisting of needle or fiber shaped crystallites
    - - Dense fibrous microstructure
    - - Columnar microsctructure
    - - Recrystallized mircrostructure
  - - - Metals and alloys as conductors, contacts, resistors and capacitors
      - Transparent conductors (e.g. undium tin oxide), and thin metals serve as electrodes for LCDs, touch panels, other display device, and solar cells
      - Extensively used in microelectronic devices
    - - Thin metal and dielectric coatings are used to construct mirrors, antireflection coatings, laser optics, and lens coatings, and to provide architectural energy control and optical data storage.
      - Low-emissivity (low-e) coatings on glass in double-pane window assemblies to reduce heat loss in winter and heat gain in summer.