Precursor Adsorption on Copper Surfaces as the First Step during the Deposition of Copper: A Density Functional Study with van der Waals Correction

Abstract

Copper dimethylamino-2-propoxide [Cu(dmap) 2 ] is used as a precursor for low-temperature atomic layer deposition (ALD) of copper thin films. Chemisorption of the precursor is the necessary first step of ALD, but it is not known in this case whether there is selectivity for adsorption sites, defects, or islands on the substrate. Therefore, we study the adsorption of the Cu(dmap) 2 molecule on the different sites on flat and rough Cu surfaces using PBE, PBE-D3, optB88-vdW, and vdW-DF2 methods. We found the relative order of adsorption energies for Cu(dmap) 2 on Cu surfaces is E ads (PBE-D3) > E ads (optB88-vdW) > E ads (vdW-DF2) > E ads (PBE). The PBE and vdW-DF2 methods predict one chemisorption structure, while optB88-vdW predicts three chemisorption structures for Cu(dmap) 2 adsorption among four possible adsorption configurations, whereas PBE-D3 predicts a chemisorbed structure for all the adsorption sites on Cu(111). All the methods with and without van der Waals corrections yield a chemisorbed molecule on the Cu( 332) step and Cu(643) kink because of less steric hindrance on the vicinal surfaces. Strong distortion of the molecule and significant elongation of Cu−N bonds are predicted in the chemisorbed structures, indicating that the ligand−Cu bonds break during the ALD of Cu from Cu(dmap) 2 . The molecule loses its initial square-planar structure and gains linear O−Cu−O bonding as these atoms attach to the surface. As a result, the ligands become unstable and the precursor becomes more reactive to the coreagent. Charge redistribution mainly occurs between the adsorbate O−Cu−O bond and the surface. Bader charge analysis shows that electrons are donated from the surface to the molecule in the chemisorbed structures, so that the Cu center in the molecule is partially reduced.

Kinetics and Coverage Dependent Reaction Mechanisms of the Copper Atomic Layer Deposition from Copper Dimethylamino-2-propoxide and Diethylzinc

“…41 We found that pure PBE predicts that physisorbed and chemisorbed structures exist on the flat Cu (111) surface depending on the adsorption sites. We also found from the Bader charge analysis that the 13 and decomposition (B1 and B2) are in Figure 3.…”

“…This involves the loosing of Cu -N coordination and the formation of metallic bonds from adsorbate Cu to surface Cu as described in detail in Ref 41 . Figure 2 shows that the transformation needs a small activation energy of 0.17 eV, which can be overcome at a typical ALD temperature, e.g.…”

“…In our previous work, we found that the vdW interaction is an important factor in describing the adsorption of Cu(dmap) 2 on copper surfaces. 41 Therefore, we now test the impact of vdW interaction on the energetics of the have a small effect on the values of the activation energies, but that the nature of the reaction mechanisms described in Figure 11 will probably not be affected.…”

“…40 Previously, we also studied the adsorption of Cu(dmap) 2 on flat and rough copper surfaces using DFT with different treatments of van der Waals (vdW) interaction. 41,42 We found that the adsorption energies and geometries of the Cu(dmap) 2 adsorbed on the Cu surfaces depend substantially on the adsorption sites and treatment of vdW interactions. Based on this in-depth investigation of the precursor, we now proceed to study the full ALD reaction cycle using Cu(dmap) 2 and the Et 2 Zn co-reagent.…”

Classification of processes for the atomic layer deposition of metals based on mechanistic information from density functional theory calculations

“…It has been found that the adsorption energies and geometries depend on the roughness of the surface and on the method to treat the van der Waals interaction in DFT. 20 Strong distortion of the molecule and cleavage of Cu− −N bonds is predicted in the chemisorbed structures, which allows these parts of the ligand to lift off the surface and avoid Cu− −C bonding, but also become reactive towards the co-reagent. The molecule gains linear O− −Cu− −O bonding and this is where charge redistribution with the surface mainly occurs.…”