ALD - Cambridge Nanotech Savannah 200

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Atomic Layer Deposition (ALD) is a technique that allows growth of thin films, atomic layer by layer, using the reaction between precursor and hydroxylated surface. For example, Al2O3 layer is grown from water and trimethylaluminum (TMA), as shown below.

  1. Put in a sample which is hydroxylated from exposure to air, oxygen or ozone.
  2. Pulse the TMA precursor; TMA will react with the OH groups on the surface. TMA does not react with itself and the monolayer formed passivates the surface.
  3. Remove unreacted TMA molecules by evacuation and/or purging with nitrogen.
  4. Pulse water (H2O) into the reactor. This will remove the CH3 groups, create Al-O-Al bridges, and passivate surface with Al-OH. CH4 (methane) is formed as a gaseous byproduct.
  5. Remove unreacted H2O and CH4 molecules by evacuation and/or purging with nitrogen.

This cycle produces a maximum of 1.1 Å of Al2O3 depending on temperature.

The following materials can be deposited:

Each recipe is found in ALD recipes in nanofab wiki (PennKey required for login) or logbook.