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ALD Tutorial

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  • Taking out cost / availability from the equation, the Must be thermally stable;Volatile / Reactive; Compatibility with substrate / manufacturing
  • Taking out cost / availability from the equation, the Must be thermally stable;Volatile / Reactive; Compatibility with substrate / manufacturing
  • MgCp2 – shows decomposition above 300C, high carbon contamination below 200
  • Transcript

    • 1. July 2011
      Cambridge NanoTech ALD Tutorial
    • 2. ALD Applications
      Other applications
      Roll to rollInternal tube linersNano-glueBiocompatibleMagnetic
      Chemical
      CatalysisFuel cells
      Semi / Nanoelectronics
      Flexible electronics
      Gate dielectricsGate electrodesMetal InterconnectsDiffusion barriersDRAMMultilayer-capacitorsRead heads
      MEMS
      Etch resistanceHydrophobic / antistiction
      Optical
      AntireflectionOptical filtersOLED layersPhotonic crystalsTransparent conductorsElectroluminescenceSolar cellsLasersIntegrated opticsUV blockingColored coatings
      Nanostructures
      Inside poresNanotubesAround particlesAFM tips
      Wear resistant
      Blade edgesMolds and diesSolid lubricantsAnti corrosion
      Cambridge NanoTech Inc. Confidential
    • 3. ALD Films
      - ALD films deposited with digital control of thickness; “built layer-by layer”
      - Each film has a characteristic growth rate for a particular temperature
      Common ALD Materials
      ALD Deposition Rates at 250°C
      Oxides
      Al2O3, HfO2, La2O3, SiO2, TiO2, ZnO, ZrO2, Ta2O5, In2O3, SnO2, ITO, FeOx, NiO2, MnOx, Nb2O5, MgO, NiO, Er2O3
      Nitrides
      WN, Hf3N4, Zr3N4, AIN, TiN, TaN, NbNx
      Metals
      Ru, Pt, W, Ni, Co
      Sulphides
      ZnS
      1.26 Å
      1.08 Å
      0.38 Å
      Cambridge NanoTech Inc. Confidential
    • 4. Benefits of ALD
      Perfect films
      Digital control of film thickness
      Excellent repeatability
      100% film density
      Amorphous or crystalline films
      Conformal Coating
      Excellent 3D conformality
      Ultra high aspect ratio (>2,000:1)
      Large area thickness uniformity
      Atomically flat and smooth coating
      Challenging Substrates
      Gentle deposition process for sensitive substrates
      Low temperature and low stress
      Excellent adhesion
      Coats challenging substrates – even teflon
      Cambridge NanoTech Inc. Confidential
    • 5. ALD Reaction Sequence
      ALD is based on the spatial separation of precursors
      A single ALD cycle consists of the following steps:
      1) Exposure of the first precursor
      2) Purge or evacuation of the reaction chamber to remove the non-reacted precursors and the gaseous reaction by-products
      3) Exposure of the second precursor – or another treatment to activate the surface again for the reaction of the first precursor
      4) Purge or evacuation of the reaction chamber
      Single Cycle
      Precursor A
      Purge
      Precursor B
      Purge
      Time
      Cambridge NanoTech Inc. Confidential
    • 6. ALD Example Cycle for Al2O3 Deposition
      Tri-methyl
      aluminum
      Al(CH3)3(g)
      Methyl group
      (CH3)
      Al
      H
      C
      H
      H
      H
      O
      Substrate surface (e.g. Si)
      In air H2O vapor is adsorbed on most surfaces, forming a hydroxyl group.
      With silicon this forms: Si-O-H (s)
      After placing the substrate in the reactor, Trimethyl Aluminum (TMA) is pulsed into the reaction chamber.
      Cambridge NanoTech Inc. Confidential
    • 7. Methane reaction
      product CH4
      H
      Reaction of
      TMA with OH
      H
      C
      H
      H
      H
      H
      C
      C
      H
      H
      H
      Al
      O
      Substrate surface (e.g. Si)
      Al(CH3)3 (g) + : Si-O-H (s) :Si-O-Al(CH3)2(s) + CH4
      ALD Cycle for Al2O3
      Trimethylaluminum(TMA) reacts with the adsorbed hydroxyl groups,
      producing methane as the reaction product
      Cambridge NanoTech Inc. Confidential
    • 8. ALD Cycle for Al2O3
      Methane reaction
      product CH4
      Excess TMA
      H
      H
      C
      C
      H
      H
      Al
      O
      Substrate surface (e.g. Si)
      Trimethyl Aluminum (TMA) reacts with the adsorbed hydroxyl groups,
      until the surface is passivated. TMA does not react with itself, terminating the reaction to one layer. This causes the perfect uniformity of ALD.
      The excess TMA is pumped away with the methane reaction product.
      Cambridge NanoTech Inc. Confidential
    • 9. ALD Cycle for Al2O3
      H2O
      O
      H
      H
      H
      H
      C
      C
      H
      H
      Al
      O
      After the TMA and methane reaction product is pumped away, water vapor (H2O) is pulsed into the reaction chamber.
      Cambridge NanoTech Inc. Confidential
    • 10. 2 H2O (g) + :Si-O-Al(CH3)2(s) :Si-O-Al(OH)2(s) + 2 CH4
      ALD Cycle for Al2O3
      Methane reaction product
      New hydroxyl group
      Methane reaction
      product
      Oxygen bridges
      H
      O
      O
      Al
      Al
      Al
      O
      H2O reacts with the dangling methyl groups on the new surface forming aluminum-oxygen (Al-O) bridges and hydroxyl surface groups, waiting for a new TMA pulse. Again metane is the reaction product.
      Cambridge NanoTech Inc. Confidential
    • 11. ALD Cycle for Al2O3
      H
      O
      O
      O
      Al
      Al
      Al
      O
      The reaction product methane is pumped away. Excess H2O vapor does not react with the hydroxyl surface groups, again causing perfect passivation to one atomic layer.
      Cambridge NanoTech Inc. Confidential
    • 12. H
      H
      H
      O
      O
      O
      O
      O
      Al
      Al
      Al
      O
      O
      O
      O
      O
      Al
      Al
      Al
      O
      O
      O
      O
      O
      Al
      Al
      Al
      O
      O
      O
      Al(CH3)3 (g) + :Al-O-H (s) :Al-O-Al(CH3)2(s) + CH4
      ALD Cycle for Al2O3
      One TMA and one H2O vapor pulse form one cycle. Here three cycles are shown, with approximately 1 Angstrom per cycle.
      Two reaction steps in each cycle:
      2 H2O (g) + :O-Al(CH3)2(s) :Al-O-Al(OH)2(s) + 2 CH4
      Cambridge NanoTech Inc. Confidential
    • 13. ALD Deposition Characteristics
      ALD is insensitive to dose after saturation is achieved
      Deposition rate remains unchanged with increasing dose
      MgO Saturation Curve at 250°C
      Linear MgO Deposition
      Cambridge NanoTech Inc. Confidential
    • 14. ALD “Window”
      • Each ALD process has an ideal process “window” in which growth is saturated
      • 15. Process parameters inside the ALD window allowfor reliable and repeatable results
      • 16. The ALD window is defined by the precursor volatility / stability
      Decomposition limited
      Condensation limited
      Growth Rate
      Å/cycle
      ALD
      Window
      Saturation
      Level
      Temperature
      Desorption limited
      Activation energy limited
      Cambridge NanoTech Inc. Confidential
    • 17. ALD Reaction Temperatures
      ALD is a chemistry driven process
      Based on precursor volatility/reactivity
      Most ALD Processes
      Reactor Temp
      >400°C
      250°C
      300°C
      150°C
      150°C
      Room T
      200°C
      100°C
      350°C
      High precursor volatility, lower thermal stability of precursors
      Lower precursor volatility, Slow desorption of precursors
      Cambridge NanoTech Inc. Confidential
    • 18. High Aspect Ratio Coatings
      ALD is uniquely suited to coat ultrahigh aspect ratio structures enabling precise control of the coatings thickness and composition.
      Cambridge NanoTech’s research systems offer deposition modes for ultra high aspect ratio (>2,000:1)
      “Capillary tube”
      Cross Sectional SEM
      AAO template*
      *Image courtesy of the University of Maryland
      Cambridge NanoTech Inc. Confidential
    • 19. Compositional Uniformity
      Refractive Index – Ellipsometry
      Cross sectional EDX
      2.104
      2.103
      2.101
      2.101
      2.105
      2.102
      2.104
      2.104
      2.101
      2.103
      2.103
      2.103
      2.099
      2.101
      2.104
      Al2O3 Silica aerogel foam
      Ta2O5 - 500Å film
      Cambridge NanoTech Inc. Confidential
    • 20. ALD Precursors
      Good ALD precursors need to have the following characteristics:
      Volatility
      Vapor pressure (> 0.1Torr at T < 200°C) without decomposition
      Stability
      No thermal decomposition in the reactor or on the substrate
      Reactivity
      Able to quickly react with substrate in a self-limiting fashion (most precursors are air-sensitive)
      Byproducts
      Should not etch growing film and/or compete for surface sites
      Availability
      Precursor cylinders
      Cambridge NanoTech Inc. Confidential
    • 21. Plasma Enhanced (PE)ALD
      • Remote Plasma as a reactant
      • 22. Expands ALD window for materials by decreasing activation energy
      • 23. Lower temperature possible: avoids precursor decomposition
      • 24. Faster deposition cycle times
      • 25. Fewer contaminates in films
      Single Cycle
      Fiji PE-ALD chamber
      Precursor A
      Purge
      Plasma On
      Plasma Purge
      Time
      Cambridge NanoTech Inc. Confidential
    • 26. Plasma Enhanced (PE)ALD
      Plasma ALD processes are used for a variety of oxides, nitrides, and metals, including titanium nitride, platinum, and other materials, allowing for low resistivity of titanium nitride, and significantly lower temperatures for depositing platinum.
      Cambridge NanoTech Fiji Manifold
      Cambridge NanoTech Fiji Chamber
      Cambridge NanoTech Inc. Confidential
    • 27. Variety of Material Types Possible
      ALD allows for the fabrication of different types of materials, all in the same deposition chamber, without the need for different hardware configurations.
      Doped films: single “layers” of dopant film in between bulk
      • Doped films do not require “activation” by annealing
      (B) Nanolaminate Films: stacks of alternating layers
      (C) Graded films: composition slowly changes from material A to material B
      M1
      Cambridge NanoTech Inc. Confidential
    • 28. Low Temperature ALD
      Some ALD processes can deposit films < 150°C: Al2O3, HfO2, SiO2, TiO2, ZnO, ZrO2, Ta2O5, SnO2, Nb2O5, MgO
      Ideal for merging organics with inorganics
      Compatible with photoresist, plastics, biomaterials
      Cambridge NanoTech Inc. Confidential
    • 29. Product Portfolio
      Cambridge NanoTech ALD systems are engineered for a wide variety of applications from research to high-volume manufacturing. These systems deposit precise, conformal and ultra-thin films on multiple substrates. Their simplified system designs yield low startup and operating costs.
      Savannah
      Fiji
      Phoenix
      Tahiti
      Compact, cost-effective system for research
      Plasma system for research
      Batch manufacturing system
      Large area manufacturing system
      Production
      Research
      Cambridge NanoTech Inc. Confidential