Multiparameter and Parallel Optimization of ReaxFF Reactive Force Field for Modeling the Atomic Layer Deposition of Copper

In this study, we
aim to develop a ReaxFF reactive force field
for simulating the reaction mechanism of copper atomic layer deposition
(ALD). To achieve this, we optimized the Cu/C, Cu/H, and Cu/N parameters
of ReaxFF and extended the existing Cu potential to describe Cu/C/H/O/N
interactions involved in Cu ALD. The parametrization procedure was
implemented through an efficient multiparameter and parallel optimization
scheme based on the Taguchi method. Using the newly developed Cu potential,
we performed reactive molecular dynamics (RMD) simulations on an “abbreviated”
ALD cycle using a [Cu­(iPr-amd)]2 (iPr-amd = N,N′-diisopropylacetamidinate) or Cu­(dmap)2 (dmap = dimethylamino-2-propoxide) precursor with the H radical
as a coreactant. In the first half-cycle, the [Cu­(iPr-amd)]2 precursor is found to adsorb dissociatively
on the Cu surface as Cu­(iPr-amd) monomers.
During the second half-cycle, H radicals partly eliminate precursor
fragments to the gas phase, but some intermediates such as C5H12N2 and C2H4N remain
on the surface and may become a source of contamination. On the other
hand, the Cu­(dmap)2 precursor dissociates into Cu­(dmap)
and dmap on the Cu surface. The second half-cycle is initiated through
a hydrogen transfer reaction, which completely eliminates the dmap
ligands to the gas phase. In general, our RMD simulations suggest
that the surface chemistry of Cu­(dmap)2 during the ALD
is simpler and cleaner than that of [Cu­(iPr-amd)]2.