錫晶粒的微結構對微凸塊之電遷移破壞模式研究

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是目前封裝技術的重要議題之一。 本實驗使用兩種不同的金屬墊層，分別為Cu/Ni/Sn2.3Ag/Ni/Cu以及Cu/Sn2.3Ag/Ni/Cu來做研究。利用不同冷卻速率，使銲錫的微結構改變，在通以8x104 A/cm2的電流密度測試，比較不同處理之試片達破壞條件所花費的時間，並觀察其電遷移破壞模式的差異。結果顯示，在Ni /Ni之結構，經過淬火處理之試片可有效減少early failure的發生，而無淬火處理之試片，錫晶粒方向會主導其達破壞條件之時間。在Cu /Ni之結構，經過淬火處理之試片雖能減少early failure的情況，但卻因晶界多，造成銅金屬墊層加速溶解進入銲錫，使得達破壞條件之時間遠比未淬火處理之試片短。

To meet the increasing demand of device densities, microbumps in three-dimensional integrated circuits have been widely adopted. Since the joint size dramatically shrinks, there is a limited number of the solder grains, and the size of each grain would play a significant role in different electromigration(EM) failure modes. In this study, we investigated effect of microstructures of Sn grains on the electromigration of microbumps. Microbumps with two different under-bump-metalligation (UBM) were adopted, inducting Cu/Ni/Sn2.3Ag/Ni/Cu and Cu/Sn2.3Ag/Ni/Cu. By varying the cooling rate during solidification, we can change the grain sizes and orientations of Sn grains. Then we conduct electromigration (EM) tests and analyze the failure mechanisms. The results indicate that, for Cu/Ni/Sn2.3Ag/Ni/Cu structure, microbumps with quench treatment have no early failure. However, for non-quenched microbumps, early failure occurs and Sn orientation dominates the failure time. For Cu/Sn2.3Ag/Ni/Cu structure, early failure can be inhabited. Nevertheless. Cu UBM dissolved into the grains boundaries of small Sn grains, resulting in fast-resistance increase of microbumps. Thus, the average failure time of quenched microbumps is shorter than that of non-quenched microbumps.