| dc.description.abstract | Nanotwinned Cu has garnered significant attention in advanced packaging technologies due to its exceptional properties. It possesses high mechanical strength, low electrical resistivity, high thermal stability, and excellent resistance to electromigration, making it an ideal material for semiconductor packaging. However, the surface roughness of nanotwinned Cu films poses challenges for practical applications. Low surface roughness plays a crucial role in enhancing the reliability of electroplated Cu films and reducing resistance, especially in 5G communication technologies where the skin effect at high-frequency AC transmission makes the impact of surface roughness on signal loss more significant.
This study explores the modification of the surface morphology of nanotwinned Cu films through temperature control. Temperature control allows for precise regulation of surface roughness by altering nucleation and growth behaviors. Additionally, to more accurately control the structure and performance of nanotwinned Cu films, this study investigates their growth mechanisms.
In exploring the growth mechanisms of nanotwinned Cu, the literature proposes two possible models: the traditional 2D nucleation and growth model and the spiral growth model. The traditional 2D nucleation and growth model can only explain smooth and uniform surface structures but fails to adequately account for the pyramidal morphology and the nucleation sites and quantity on nanotwinned Cu film surfaces. Thus, this study assumes a spiral growth model that better fits the surface morphology characteristics, conducting a series of thermodynamic derivations to establish a theoretical relationship between temperature and pyramid slope. According to the spiral growth model, an increase in temperature should increase the critical nucleation radius, decrease the pyramid slope, and reduce surface roughness. However, experimental results show that as temperature increases, the pyramid slope also increases, contradicting the theoretical predictions of the spiral growth model, indicating that the growth mechanism of nanotwinned copper might not be spiral growth.
Therefore, this study first analyzes the role of additives during the electroplating process and the effect of temperature on the adsorption/desorption behavior of additives. Combining these factors, a new additive-induced 2D nucleation and growth model is proposed: under low-temperature conditions, high additive adsorption concentration and strong inhibition enhance the secondary nucleation overpotential, favoring the formation of low-slope but sharply pyramidal surfaces; at high temperatures, the opposite occurs, resulting in high slopes but smoother surfaces.
In summary, by lowering the electroplating temperature to enhance inhibition, the pyramid slope of nanotwinned Cu films can be effectively reduced further decreasing surface roughness and significantly enhancing their applicability. The proposed new model for nanotwinned Cu growth elucidates the role of additives and the nucleation and growth behavior of surface Cu adatoms, clarifying the growth mechanisms of electroplated nanotwinned Cu. Future attempts could explore enhancing inhibition through other methods such as increasing the electric field, further reducing surface roughness without significantly affecting the growth mechanism of nanotwinned Cu. | en_US |