Fabrication and thermal stability of highly (111)-oriented nanotwinned Cu films and their applications in 3D IC packaging
|關鍵字:||奈米雙晶銅;三維積體電路;冶金反應;熱遷移;微凸塊;nano twin Cu;3D IC;inter metallurgy;thermomigration;microbump|
|摘要:||本論文研究(111)奈米雙晶銅膜的製備，熱穩定性及其在封裝業的應用。內容共分為五章，第一部分探討以脈衝電鍍方式，製備具高度(111)優選方向之奈米雙晶銅膜及導線，透過退火之熱處理，觀察奈米雙晶銅膜及導線在300oC一小時退火後，具有良好的熱穩定性，同時亦觀察試片經由退火後之晶粒成長情形，試片內部之柱狀奈米雙晶銅往下成長將底層之隨機方向細晶粒區轉變成柱狀奈米雙晶結構，且具(111)優選方向，使得銅膜及導線之(111)優選方向更加提升以及更一致的結構。具高熱穩定性的奈米雙晶銅在第二到第六部分應用於3D IC封裝之銅金屬墊層中。第二部分探討銅原子在Cu/SnAg/Cu系統中的熱遷移情形，在一存在溫度梯度的液態銲錫中，迴焊反應後微凸塊的介金屬化合物呈不對稱生長，原因為銅原子的熱遷移所致。第三部分則探討銲錫厚度對於Ni/SnAg/Cu微凸塊迴焊時之介金屬化合物生長及銲錫內部濃度梯度之影響。微凸塊之銲錫厚度從10 μm增加到60 μm，銅端與鎳端的介金屬化合物生長速率會因為銲錫內部銅、鎳之濃度梯度而產生變化。第四部分則研究Ni/SnAg/Cu系統中的熱遷移情形，此為二、三部分之延續，可看到當銅原子的熱遷移及銅、鎳濃度梯度在微凸塊晶迴焊時之介金屬化合物生長，從中得知銅原子之熱遷移為影響介金屬化合物生長速率的主要因素。第五部分探討不同銲錫厚度之Cu/SnAg/Cu微凸塊在固態高溫儲存測試時，內部介金屬化合物之生長情形，經由1000小時於150oC高溫儲存後，可發現當微凸塊當中之銲錫被消耗完畢轉變成Cu6Sn5後，於兩端之Cu3Sn之成長速率將顯著增加。且使用奈米雙晶銅所製備之金屬墊層，使用聚焦離子束蝕刻後，發現在Cu3Sn與銅金屬墊層之交界上幾乎沒有Kirkendall void，可提升微凸塊之可靠度。|
This study investigates the fabrication, thermal stability, and applications in microelectronics packaging. This dissertation contains five parts. In the first part, we discussed the fabrication of highly (111)-orientated nano-twinned copper by pulse plating. After annealing at 300oC for an hour, the nano-twinned copper showed good thermal stability. Moreover, the columnar nano-twinned grain grew to the bottom side and transformed the fine grain region into columnar nano-twinned structure with (111)-preferred orientation. The (111)-orientated nano-twinned copper with good thermal stability was applied to the Cu lines and under bump metallization (UBM) in the second to sixth parts. In the second part, we observed the thermomigration of Cu atom in Cu/SnAg/Cu microbumps. Micro bumps were reflowed under a temperature gradient. After reflow, there was asymmetrical intermetallic compounds (IMCs) growth due to the thermomigration of Cu atoms. In the third part, we discussed the effect of solder thickness to the IMC growth in Ni/SnAg/Cu microbumps. The thicknesses of solder were from 10 to 60 μm. IMC growth rates were changed with the concentrations of Ni and Cu. In the fourth part, the thermomigration of Cu atom in Ni/SnAg/Cu micro bump was observed. There are two factors, which are thermomigration of Cu atoms and concentration gradient of Cu and Ni, to affect the IMC growth in Ni/SnAg/Cu microbumps. The main factor which dominated the IMC growth is thermomigration of Cu atoms. In the fifth part, we discuss the effect of solder thicknesses to IMCs growth in Cu/SnAg/Cu micro bump after high temperature storage. After 1000-hr-150oC aging, the growth rate of Cu3Sn increased when all the solder was consumed. Moreover, the microbumps were also polished by focus ion beam to observe the microstructure. We found that there were few Kirkendall voids on the interface of nano-twinned Cu UBM and Cu3Sn. These results indicated the use of nano-twinned Cu can improve the reliability of microbumps.