Oxford Instruments posted a archive of their Plasma ALD webinar. Professor Erwin Kessels describes the thermal ALD and Plasma ALD process steps. The process includes four generals steps.

1. Precursor exposure
2. Purge
3. Reactant exposure
4. Purge

Thermal ALD takes place at temperatures between 150 to 400°C. Using plasma ALD reduces deposition temperatures by 100-150°C. Many materials can be deposited at room temperature with fair to good characteristics. The four step process is repeated multiple times to build up a film layer-by-layer to the precise thickness desired. The reactants must produce a self-limiting reaction on the substrate surface to be considered ALD. The merits of plasma ALD include:

• Improved material properties
• Deposition at lower temperatures
• Increased choice of precursors and materials
• Good control of film stoichiometry and film composition
• Increased growth rates
• More process versatility generally

Plasma ALD challenges include

• Reduced conformity or step coverage
• Plasma induced damage (ion bombardment and UV damage)
• Industrial scale up more complex

For more information, see Atomic layer deposition of nanostructured materials by professor Kessel, and Vacuum Science Technology A 29 050801 (2011) Profijt et. al.