三維積體電路之微凸塊電遷移可靠度議題研究

Abstract

在電子元件微縮化和多功能化的趨勢下，電子封裝致力於發展三維封裝技術，其中用銲錫微凸塊作晶片間的連接，然而銲錫接點縮小所造成的可靠度問題目前鮮少有研究提及。本實驗利用銲錫高度10微米的銅／鎳／錫銀／鎳微凸塊結構在不同溫度下做電遷移測試，結果顯示，隨著溫度增加，邊牆擴散效應影響越發顯著，在電流密度為6x104 A/cm2電遷移測試中，會造成銅溶解的方式不同。在170 °C的電遷移測試下，由於介金屬化合物快速生成，加上邊牆擴散效應顯著，因此破壞模式趨於孔洞生成；用同步輻射研究中心的17B做X光繞射，發現銲錫內部的錫晶粒有許多方向訊號出現，利用電子背向散射繞射儀分析銲錫內部錫晶粒方向，探討在125 °C下受電遷移測試的微凸塊中微結構變化，發現錫晶粒方向對破壞模式影響較為顯著，因此在相同測試條件下會有出現不同的破壞模式。

Due to the growing demand for small and multi-functional electronic devices, three dimensional integration circuits have gotten much attention recently. Electromigration reliability issues might occur because solder bumps become smaller. In this study, we used microbumps with 10 micrometer bump height and Cu/Ni/Sn2.0Ag/Ni structure to study the effect of temperature on electromigration. The applied current density was 6×104 A/cm2. When temperature increased, side-diffusion effect became more seriously, which led the dissolution of copper in bumps differently. At 170 °C, the growth of intermetallic compounds and side-diffusion effect were more serious during electromigration, so the failure mechanism was mainly void formation. In the X-ray diffraction results, Sn grains in microbumps were randomly oriented. We studied Sn grain orientation effect on electromigration failure mechanism at 125 °C by electron backscatter diffraction. We found out that Sn grain orientation played a more important role on the failure mode in low temperatures than high temperatures. So when we tested the samples in same current density at different temperatures, electromigration failure modes were quite different.