Implementation of
vapor/phase dosing of small molecule inhibitors
(SMIs) in advanced atomic layer deposition (ALD) cycles is currently
being considered for bottom-up fabrication by area-selective ALD.
When SMIs are used, it can be challenging to completely block precursor
adsorption due to the inhibitor size and the relatively short vapor/phase
exposures. Two strategies for precursor blocking are explored: (i)
physically covering precursor adsorption sites, i.e., steric shielding,
and (ii) eliminating precursor adsorption sites from the surface,
i.e., chemical passivation. In this work, it is determined whether
steric shielding is enough for effective precursor blocking during
area-selective ALD or whether chemical passivation is required as
well. At the same time, we address why some ALD precursors are more
difficult to block than others. To this end, the blocking of the Al
precursor molecules trimethylaluminum (TMA), dimethylaluminum
isopropoxide (DMAI), and tris(dimethylamino)aluminum (TDMAA)
was studied by using acetylacetone (Hacac) as inhibitor. It was found
that DMAI and TDMAA are more easily blocked than TMA because they
adsorb on the same surface sites as Hacac, while TMA is also reactive
with other surface sites. This work shows that chemical passivation
plays a crucial role for precursor blocking in concert with steric
shielding. Moreover, the reactivity of the precursor with the surface
groups on the non-growth area dictates the effectiveness of blocking
precursor adsorption.