奈米多孔銅薄膜製程與分析：由磁控濺鍍到去合金法

Synthesis and Characterization of Nanoporous Copper Thin Films by Magnetron Sputtering and Subsequent Dealloying

李宇蓁(Yu-Zhen Lee)

指導教授 ： 鄭憶中

國立臺灣大學/工學院/機械工程學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201902848

摘要

奈米多孔金屬具有低相對密度、高表面積及極佳的熱、電傳導特性，因此非常適合應用在化學催化、感測器、電池等地方。然而，藉由機械加工(如Melt Spinning)得到的薄片受限於尺寸與形狀上的限制，而透過共濺鍍方式得到的薄膜不僅能夠更加精準的控制薄膜厚度，且不受限於底材，還能透過功率調整得到具不同合金組成的雙層或多層薄膜，因而更加拓展奈米多孔金屬的應用領域；此外，對於奈米多孔薄膜的研究，多著重於金、銀、鈀等貴金屬，鮮少有文獻針對奈米多孔銅薄膜做研究，且相對於貴金屬，銅具有成本上的優勢，更適合做為工業上的應用。
本研究利用共濺鍍的方式，將銅、鋁共鍍於矽基板上，透過調整功率與濺鍍時間得到合金成分為 22-37at% Cu-Al，薄膜厚度為0.5-1.5 μm的前驅合金鍍層，再利用0.5-1M NaOH 腐蝕時間為5-60分鐘進行化學去合金後，得到不同結構的奈米多孔銅薄膜。去合金前後的試片均會利用SEM及EDS進行表面形貌與成分分析，橫截面則是藉由FIB切片觀察，並利用XRD進行結晶性分析，機械性質分析則是透過奈米壓痕試驗機來測試。
本研究探討前驅鍍層的合金組成、薄膜厚度、腐蝕液濃度與腐蝕時間對於去合金過後的奈米多孔銅(Nanoporous Copper, NPC)薄膜結構及其機械性質之影響。由實驗結果得到Ligament Size為19-77nm的NPC薄膜；去合金前後均有氧化現象(>50 at%)；去合金後的試片仍有少量鋁的殘留，且不隨腐蝕時間增加而減少；具有較低含量銅(22at%)的前驅鍍層會造成去合金過後NPC產生較多孔洞，隨銅含量的增加(30at%→37at%)，Ligament會由原本均勻分布轉變成彼此聚集，造成支架尺寸分布較不均勻；膜厚為1.5μm的試片在去合金過後會有明顯裂紋生成，且會隨著腐蝕時間增加而逐漸減少，反之，膜厚為0.5μm的試片在去合金過後則沒有裂紋明顯生成；NaOH濃度變化並沒有對NPC薄膜結構造成明顯的改變；腐蝕時間增加會造成Ligament的粗化並讓裂紋減少；由奈米壓痕試驗得到NPC薄膜硬度介於129-254 MPa間。

關鍵字

奈米多孔銅薄膜 ； 共濺鍍 ； 化學去合金 ； 機械性質

並列摘要

Recently, nanoporous metals (NPMs) have raised increasing attentions due to their high surface, low relative density, excellent electrical and thermal conductivity which broader their applications in many fields such as catalysis, sensing, battery and so on. Up till now, researches upon the synthesis of NPM films via magnetron sputtering mostly focus on noble elements (e.g. Au, Ag, Pd, etc.). In comparison, nanoporous copper (NPC) can attract much more interests because of its huge cost saving in practical use, while maintain high functionality at the meantime.
In this study, nanoporous copper films with ligament sizes ranging from 19 to 77 nm were fabricated by dealloying 22-37at% Cu-Al precursor films with thickness ranging from 0.5 to 1.5 μm. The precursor alloy films were deposited on silicon (100) via magnetron co-sputtering. The as-deposited films were then chemical dealloying in alkaline solution to fabricate NPC films. Effect of chemical composition and thickness of precursor alloy, concentration of dealloying solution and dealloying time on morphology and mechanical behavior of NPC films were investigated. Microstructure and the chemical composition of the as-deposited and as-dealloyed films were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), while focus ion beam (FIB) was employed for cross section observation. The hardness of nanoporous copper films was determined via nanoindentation.
From experiment results, there are still slight residual Al that can be detected in NPC films, even with the increasing of dealloying time. Oxidation in as-deposited precursor and as-dealloyed NPC films is unavoidable. The ligaments of NPC films transformed from well-distributed to cluster with composition of Cu in precursor alloy increasing from 22at% to 37at%. Cracks resulting from dealloying process appeared in NPC films with thickness of 1.2 to 1.4μm, while there were no obvious cracks appeared in NPC films with thickness of 0.5μm. The concentration of NaOH showed no significant effect on the structure of NPC films. The coarsen of ligaments and the healed of cracks were resulting from the increasing of dealloying time. NPC films with hardness ranging from 129 to 254 MPa were obtained by nanoindentation test.

並列關鍵字

nanoporous copper films ； magnetron co-sputtering ； dealloying ； mechanical behavior

參考文獻

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