ALD : saturated surface-controlled reaction

  • Substrate is exposed to the first molecular precursor.
  • The first molecular precursor is retained on the surface by chemisorption.
  • Second precursor is introduced on the surface, which reacts on the surface of the first precursor.
  • Exchange reaction takes place between the two precursors and by-products are formed.
  • Exchange reaction continues till the second precursor reacts with first precursor.
  • Final reaction : Precursor A + Precursor B → Film AB + by-products
  • Sequence is repeated to grow films required.
ALD-Basic-01

Advantages of Atomic Layer Deposition

  • Atomic layer deposition has several advantages over other techniques due to the actual mechanism used to deposit films.
  • ALD is especially advantageous when film quality or thickness is critical.
  • ALD is also quite effective at coating ultra high aspect ratio substrates or substrates that would be difficult to coat with other thin film techniques.
  • Perfect films:
    • Digital thickness control to the atomic level by depositing film one atomic layer at a time-pinhole-free films, over very large areas
    • Excellent repeatability
    • Wide process windows(no sensitivity to temperature or precursor dose variations)
    • Low-defect density
    • Amorphous or crystalline, depending on substrate and temperature
    • Digital control of sandwiches, hetero-structures, nanolaminates, mixed oxides, graded layers, and doping
    • Insensitivity to particle
    • Standard recipes for oxides, nitrides, metals, and semiconductors
  • Conformal coating :
    • Perfect 3D conformality and 100% step coverage : uniform coatings on flat, inside porous, and around particle samples
    • Flat and smooth coating that copies shape of substrate perfectly
    • Large area thickness uniformity
    • Easy batch scalability
  • Challenging substrates:
    • Gentle deposition process for sensitive substrates, no plasma needed
    • Low temperature deposition possible (RT~400˚C)
    • Coats everything, even on teflon
    • Excellent adhesion due to chemical bonds at the first layer
    • Low stress due to molecular self-assembly