## 3 Results and Discussion
### Deposition Rate  
The dominant factor of different deposition rates is the collision of depositing and deposited atoms, and the effect of Ostwald ripening. With a higher deposition rate, the energy transferred by the depositing atoms to the deposited atoms increases, giving the copper atoms more energy to flow to the low deposited area, while with a lower deposition rate, more surface diffusion of Ostwald ripening occurs due to longer deposition time. The copper seed layer with different deposition rates is shown in Figures 23 and 24 and illustrates the overall distribution of the deposited copper atoms with respect to deposition rates.  
Figure 23: Copper seed layer with different deposition rates.  
Figure 22: Alloy percentage with different incident angles.  
The energy transferred between atoms occurred at a high deposition rate, i.e., at the rate of 50 atoms/ps and 30 atoms/ps in this study, while surface diffusion dominated at a low deposition rate under 10 atoms/ps. Under the circumstances of high deposition rate, by increasing the deposition rate, the energy transferred from the depositing atoms to the deposited atoms at the wing of the trench made them flow into the trench and accumulate at the top sidewall. The cluster atoms at the top sidewall also flowed into the trench, which caused the necking to increase.  
To the mid sidewall and lower sidewall, the number of atoms increased significantly at the mid sidewall as atoms from the top sidewall flowed into the trench. The number of atoms at the lower sidewall, however, decreased, as many copper atoms accumulated in a huge cluster rather than depositing to the area below the mid sidewall. As for the bottom of the trench, the large cluster at the sidewall received most of the depositing atoms towards the bottom of the trench, thus decreasing the number of atoms at the bottom of the trench. It is also noted that since the deposition rate of 50 atoms/ps received more energy from the depositing atoms, atoms at the bottom center flowed toward the two sides, and the atoms at the two sides flowed to the lower sidewall. This increased the number of atoms at the lower sidewall and the bottom side and decreased the number of atoms at the bottom center.  
Under the circumstances of low deposition rate, by decreasing the deposition rate, there was no additional energy given by the depositing atoms for the atoms at the wing to break through the diffusion barrier energy, while Ostwald ripening caused the atoms on the top sidewall to flow towards the wing of the trench. This caused an increase in number of atoms at the wing and a decrease in number of atoms at the top sidewall, which also led to an increase of the necking. At the mid sidewall and lower sidewall, the increase of necking decreased the shadowing effect, which caused the depositing atoms at the mid sidewall and lower sidewall to increase. To the bottom of the trench, with the increasing necking, more atoms arrived at the bottom trench, and thus the number of atoms at the bottom center and bottom side increased. These phenomena led to the results of the step coverage, uniformity, necking, and bottom height shown in Figures 25-27. It was also observed that as the deposition rate decreased, energy transferred from the depositing atoms to the substrate decreased, which decreased the alloy percentage significantly, as shown in Figure 28.  
Figure 25: Step coverage with different deposition rates.