In our previous work , we used a 29 atom model of Cu in order to gain better insight into the behaviour of a Cu model with larger number of atoms at a different stage of the film growth process. We use this model on the most promising Co-and W-doped TaN surfaces from Sections 3.2 and 3.3 and assess our predictions of 2D vs 3D Cu morphology based on Cu-Cu and Cu-substrate interactions. The surfaces selected are Co 25 , Co 50-F , W 25 , W 50-F and W 100 . Similar to Ru-doped TaN surfaces, we observe a transition from the initial single layer of Cu 29 to a two-layered structure on all surfaces. On Co 25 , 7 Cu atoms move to the second layer, while on Co 50-F 6 atoms migrate to form a second layer, as shown in Figure . On both W 50-F and W 100 , the Cu structure resembles facets on the Cu(1 1 1) surface. This is the desired crystal structure for Cu in interconnects as it has the best electromigration reliability. On W 25 , 6 Cu atoms migrate into the second layer and the overall geometry continues to resemble the original Cu 29 geometry, as shown in Figure . On W 50-F there are 10 atoms in the second Cu layer and on W 100 there are 9 atoms in the second Cu layer. During the aiMD calculation the atoms rearrange to be more close packed. There are no transitions to a third layer observed over the course of 5 ps on W 100 , however a Cu atom migrates to the third layer on W 50-F after approximately 2 ps. Further upward migration occurs, creating a 3D cluster structure shown in Figure . The reduced number of atoms in the second layer of Cu 29 on Co-doped TaN compared to W-doped TaN shows that Co doping is better at preventing upward migration, as expected given the more favourable adhesion between Cu and Co as compared to Cu and W.