隨著科技的日新月異,消費者對電子產品的效能有更高的需求,3D-IC因故成為電子封裝的主流,微型化的效應使得散熱變得相當重要,因為焦耳熱效應產生過高的溫度會造成元件快速失效,而散熱的過程中又會在微小的電子元件內造成一定的溫度梯度,此溫度梯度亦會造成元素的熱遷移導致元件失效,所以在追趕更高效能的元件時,這些物理限制是我們需要研究並解決得議題。
因為許多人正提倡著鈷是一個理想的底層金屬薄膜 (under-bump metallization (UBM)）材料替代者,因此我們取鈷/錫銀/鈷試片施加2220K/cm的熱梯度去觀察其熱遷移情形,由本研究發現鈷原子並不會受到此熱梯度的驅動而擴散,而在此熱梯度下擴散主宰元素是無鉛焊錫中的錫,當0-150小時的時候,錫原子受熱驅動不停往熱端擴散,在熱端造成了錫的擠出,並抑制了原本應該生成更快的介金屬化合物CoSn3 ,使得冷熱兩端的介金屬化合物厚度相差不遠,此情形與銅和鎳UBM材料會導致兩界面非對稱成長有明顯不同,隨著介金屬化合物快速變厚,溫度梯度小於誘發錫熱遷移的臨界梯度後,錫源子擠出的現象停止,去而代之的是CoSn3的快速生成,當CoSn3生成接近20μm左右會產生裂縫阻礙進一步的介金屬化合物成長。

To meet the demands of high performance and small feature sizes of electronic products, three-dimensional integrated circuit (3DIC) technology is proposed as a promising way to overcome Moore’s law. However, the miniaturization of electronic products may bring about the serious heat issues. Because the higher temperature induced by Joule heating effect will make the electronic products quickly fail. To effectively remove heat, a temperature gradient must be established across the solder joint ; the temperature gradient would also cause the thermomigration of elements, and it finally leads to failure in Pb-free microbumps. Therefore, it is critical to understand the behavior of thermomigration of microbump .
Cobalt has been regarded as a promising candidate for under bump metallization (UBM) material, In this study, a Co/SnAg/Co sandwich structure was used to investigate the microstructure evolution and interfacial reaction of IMC in solid-state micro-scale solders under a thermal gradient of 2220 K/cm.
The results found that Co atoms would not be driven by thermal gradient of 2220 K/cm, and the dominate diffusing species under this thermal gradient is Sn. Sn atoms were observed to move toward the hot end during test period between 0-150 h, leading to mass protrusion on the hot end and voids formation at the cold end. In addition, due to the protrusion of Sn on the hot end, the interface growth of CoSn3 at the hot end were retarded and no significant difference of IMC thickness was found at the hot and cold interface. With increasing thickness of IMC at both interfaces, temperature gradient gradually decreases. While the temperature gradient is lower than 1000 K/cm , thermomigration of Sn stopped and growth rate of IMC triggered by chemical potential gradient become fast.
Furthermore, due to fast growth of CoSn3 after 180 h,cracks were found at the interface between IMC and solder. These cracks further blocked the supply of Sn and further prevent the growth of IMC at the hot and cold end.

目錄
摘要 i
ABSTRACT ii
致謝 iii
目錄 iv
表格目錄 vi
圖目錄 vii
第一章 簡介 1
第二章 文獻回顧 3
2.1 三維立體封裝的問題 3
2.2 熱遷移 6
2.2.1 熱遷移的基礎原理 6
2.2.2 在覆晶焊錫中焦耳熱誘發溫度梯度 7
2.2.3 在無鉛焊錫中的熱遷移 11
2.3 UBMs 材料的熱遷移 14
2.4 錫鈷系統介面反應 19
2.4.1 錫鈷介面反應 19
2.4.2 錫鈷銅介面反應 23
2.5 動機 25
第三章 實驗過程 26
3.1 試片製備 26
3.2 鈷/錫銀/鈷(銅)熱遷移實驗的設置 26
3.3 鈷/錫銀/銅三明治結構熱遷移 27
3.4 等溫實驗設置 27
3.5 ANSYS WORKBENCH 模擬熱梯度分佈 28
3.6 奈米壓痕記號點 28
3.7 維克氏壓痕記號點 28
第四章 結果 31
4.1 鈷/錫銀/鈷(銅)三明治結構的溫度分佈模擬 31
4.2 等溫時效下鈷/錫銀/鈷樣品的微結構變化 34
4.3 溫度梯度下鈷/錫銀/鈷樣品的微結構變化等 44
4.4 溫度梯度下鈷/錫銀/銅樣品的成分變化 56
4.5 奈米壓痕記號點 64
第五章 討論 68
5.1 在鈷/錫銀/鈷試片中CoSn3受溫度梯度驅動下的成長機構 68
5.1.1 鈷/錫銀/鈷試片等溫實驗與熱遷移實驗的比較 68
5.1.2 鈷/錫銀/鈷熱遷移實驗中介金屬化合物成長機制 70
5.2 錫熱遷移的理論證明與計算 76
第六章 結論 78

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