Rough surface formation in thin films during annealing occurs with several materials. Increased roughness of an aluminum (Al) thin film surface can lead to electrical shorts, which are a significant problem for interconnections in liquid-crystal displays. Surface roughness can be decreased by adding a small amount of other metal into Al thin film. However, the mechanism through which roughness is decrease by an alloy is not well understood. This work simulates 3D molecular dynamics of Al thin film growth to determine whether surface roughness and substrate temperature are correlated. The interaction between Al atoms is the embedded-atom-method (EAM) potential. Simulations were performed with the substrate temperatures of 300-700 K. Thin film surface roughness decreases as substrate temperature increases from 300 K to 600 K. Nevertheless, film surface roughness increases abruptly at 700 K. Simulation results are in a good agreement with other published experimental results. To investigate the effects of adding tantalum (Ta) atoms on Al thin film surface roughness, simulations of Al thin film growth with different amounts of Ta atoms and a substrate temperature of 700 K were performed. The Ta atoms were blended into the Al thin film uniformly during thin film growth. The addition of Ta atoms decreases thin film surface roughness. Furthermore, surface roughness decreases as the amount of Ta atoms in the Al-Ta alloy thin films increases. However, surface roughness increases when Ta content exceeds 4 at.% Ta. Simulation results demonstrate that the saturation point for Ta atoms for surface roughness in Ta-Al alloy thin films is the same as that obtained experimentally.