微陽極導引電鍍法製作微銅柱之研究

Research of Fabricating Copper Microcolumn by Micro Anode-guided Electroplating

探討微陽極導引電鍍法之理論以及兩極偏壓與間距對質量傳輸造成之影響，並間接影響微銅柱之形貌。以固定間距（10μm）並控制微陽極（白金線直徑125μm）以間歇運動自陰極（1公分見方之鍍銅矽晶片）表面向上移動，施加偏壓（2.6 V、2.8 V、3.0 V及3.2 V）在硫酸銅鍍液下進行微電鍍研究。另一方面則是固定偏壓（2.6 V），以不同間距（1、5、20及40μm）析鍍並進行研究。微銅柱之表面形貌以掃描式電子顯微鏡進行觀察，結果發現:銅柱形貌受兩極偏壓大小影響極大。偏壓為2.6 V時，銅柱的表面平滑柱徑平均;偏壓為3.2 V時，銅柱表面凹凸不平外觀如珊瑚狀。兩極間距越小（1μm），微銅柱柱徑較不平整會有節狀出現，兩極間距越大（40μm），微銅柱較平整但柱徑較大。本研究選擇電位從2.6 V至3.2 V，由於成長速率過慢，微陽極導引電鍍法不適用於低於2.6 V，而高於3.2 V銅柱外觀型態並不理想。最後，歸納得出微銅柱製作之最佳條件並提出微電鍍之機制。

Micrometer copper columns (roughly 50 μm in diameter) were fabricated by a patented process named as micro anode guided electroplating (MAGE). In this process, a micro anode (made of Pt wire 125μm in diameter) was controlled to depart from the cathode intermittently (1×1 cm2 silicon coated with 1.8μm copper) under optimed biases to fabricate copper micro-columns in an acidic CuSO4 bath(CuSO4．5H2O 200 g/L，H2SO4 65 g/L and 35 g/L, HCl 1mL). The surface morphologies of the copper micro columns, examined by scanning electron microscopy (SEM), depended on the bias applied between the electrodes. The microcolumn obtained at a bias of 2.6 V, displayed uniform diameter and smooth surface. In contrast, the micro column fabricated at a bias of 3.2 V was coralline and displayed rough surface. The sem morphology of microcolumns was also influenced by the gap in each intermittent step. A short gap (e.g. 1 μm) led to nodose microcolumn with rough surface but a long gap (e.g. 40 μm) led to uniform microcolumn with smooth surface. In this work, practical range of bias was chosen from 2.6 to 3.2 V because the growth rate of the microcolumn was to slow under biases less than 2.6 V, and coralline microcolumn was not acceptable under biases greater than 3.2 V. In comparison with the microcolumns fabricated in various conditions, we obtained the optimal conditions to attain the qualified copper microcolumns.