Atomic Layer Deposition (ALD)
Sample preparation
Silicon
ALD proceeds from the Si-OH bonds on the silicon surface. OH bonds are natively present in the silicon native oxide, and thus a clean sample should react without further preparation.
A silicon sample may be prepared with a highly activated surface with a piranha clean (Thian 2016), or a plasma step in the Fiji itself. For a piranha cleaned surface, it is recommended to do a 5-10 minute piranha step, remove the oxide in BOE (~8 s), then do an additional 5-10 minute piranha step. Note that piranha will increase roughness of the surface. Any freshly HF/BOE dipped silicon sample will require either time for the native oxide to regrow, or a plasma conditioning step before growth can take place. The Si-H terminated surface after an HF/BOE dip will not react with the ALD precursors (Thian 2016).
Frequent Questions
When I grow an aluminum oxide coating in the ALD, is it Al2O3? Is it Sapphire?
When ALD aluminum oxide is grown, it is typically not stoichiometric Al2O3, and is better refereed to as AlOx or AlOx. Regardless, the layer will be amorphous.
Review Articles:
Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process
Potentially useful references:
- Growth of crystalline Al2O3 via thermal atomic layer deposition: Nanomaterial phase stabilization
- Crystallization behavior of thin ALD-Al2O3 films
- Characterization of Al2O3 Thin Films Prepared by Thermal ALD
- Interface and Material Characterization of Thin ALD-Al2O3 Layers on Crystalline Silicon
- Aluminum oxide from trimethylaluminum and water by atomic layer deposition: The temperature dependence of residual stress, elastic modulus, hardness and adhesion
- Chemically Stable Atomic-Layer-Deposited Al2O3 Films for Processability
- Recent progress of atomic layer deposition on polymeric materials