| 摘要: | 奈米雙晶銅（nanotwinned Cu）因其卓越的性能在先進封裝技術中備受關注。它具有高機械強度、低電阻率、高熱穩定性和優異的抗電遷移能力，使其成為半導體封裝的理想材料。然而，奈米雙晶銅薄膜表面較為粗糙，這對其實際應用提出挑戰。低表面粗糙度對電鍍銅薄膜在提高元件可靠性和減少電阻方面具有重要作用。尤其在5G通信技術中，高頻交流電傳輸下，趨膚效應使得表面粗糙度對信號損失的影響更加顯著。
本研究藉由溫度控制的方法來改變奈米雙晶銅薄膜的表面形貌。溫度控制能透過改變成核與成長行為來精確控制表面粗糙度。同時，為了能夠更精準地控制奈米雙晶銅薄膜的結構及性能，本研究探討了其生長機制。
在探討奈米雙晶銅的生長機制時，文獻提出了兩種可能的模式：傳統的2D成核與成長模型和螺旋生長模型。傳統的2D成核與成長模型只能解釋平滑且均勻的表面結構，但無法合理解釋奈米雙晶銅薄膜表面的金字塔形貌及成核位置與數量。故本研究假設較符合表面形貌特徵得螺旋生長作為模型，並進行了一系列熱力學推導，得出了溫度與金字塔斜率之間的理論關係。根據螺旋生長模型，溫度提高使臨界成核半徑增加，金字塔斜率應減小，表面粗糙度應降低。然而，實驗結果顯示，隨著溫度升高，金字塔斜率增加，這與螺旋生長模型的理論預測相悖，表明奈米雙晶銅的生長機制可能並非螺旋生長。
因此，本研究首先分析了電鍍過程中添加劑在的功用以及溫度對添加劑吸附/脫附行為的影響，結合兩者提出了一種新型的添加劑誘導的2D成核與成長模型：低溫條件下，添加劑吸附濃度高，強抑制作用提升了二次成核過電位，有利於形成低斜率但表面具有巨型台階及尖銳的金字塔形貌；高溫則相反，斜率高但表面平滑。
總結，通過降低電鍍溫度以增強抑制作用，可以有效降低奈米雙晶銅薄膜的表面金字塔型貌的斜率進一步降低表面粗糙度，大幅提升其應用性。所提出的新型奈米雙晶銅生長模型闡述了添加劑的作用及表面銅吸附原子成核與成長行為，使電鍍奈米雙晶銅的生長機制更加明朗。未來可嘗試通過提高電場等其他方法來增強抑制作用，在不大幅影響奈米雙晶銅生長機制的情況下，進一步降低表面粗糙度。
;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. |
