2. Challenges for ALD simulation

The ALD process is fundamentally based on a mastery of interaction chemistry reduced to simpler, and therefore more controllable, expressions, compared with more conventional "non-pulsed" vapor deposition techniques. Indeed, ALD relies on self-limited reactions of a mono-molecular gas with a substrate whose surface presents suitable chemical terminations. This means that an atomic monolayer can be deposited at each ALD cycle. Gas-phase reactions are thus outlawed, and surface reactions should in principle be limited to a few standard reactions. In addition, purging phases between deposition steps ensure optimum cleanliness and avoid gas-phase interactions.

A key issue for ultra-thin layers is their ability to maintain an optimum interface with neighboring layers in contact. In this respect, the very first layers deposited using the ALD technique are fundamental....