3D IC 微凸塊電遷移研究

Abstract

三維積體電路(3D IC)已成為一個能比傳統覆晶封裝技術提供更高效能的關鍵科技。在 3D IC 技術中，不同的矽元件可以垂直且更短線長的方式連接。經由不同的方法，直徑 約20 微米(μm)的微凸塊焊錫(micro bump)被用為晶片間的接合材料，與覆晶封裝技術 中使用的焊錫比起來，微凸塊銲錫只有其五分之一的高度及二十五分之一的接觸面積。 因此微凸塊焊錫中的電流密度將達到104A/cm2 而電遷移(EM)效應將成為一個非常重要的 可靠度議題。由於微凸塊銲錫中焊錫的量較少，電遷移效應預期與傳統覆晶技術中的焊 錫凸塊相比(高度約為70-100μm)將有相當大的不同。 在此為期三年的計劃中，我們將製作微凸塊焊錫間距為40μm 之電遷移測試結構試 片並且研究其中的電遷移效應。第一年的計劃中，我們將透過封裝公司設計電遷移試片 的線路及製作微凸塊銲錫。同時也將研究傳統覆晶技術中的焊錫凸塊之電遷移效應，其 銲錫凸塊高度約為5 至20 μm 並非常接近微凸塊銲錫的高度。在第二及第三年，我們 將同時研究在低高度之覆晶技術焊錫及微凸塊銲錫中的電遷移效應及熱遷移效應。這項 計畫將為了解微凸塊銲錫在3D IC 中的電遷移效應及熱遷移效應帶來重要的進展。

Three-dimensional integrated circuit (3D-IC) has emerged as a critical technology to offer higher performance than traditional flip-chip technology. With 3D-IC technology, dissimilar Si devices can be stacked vertically with much shorter interconnection lengths. Among different methods, microbumps with a diameter of approximately 20 μm have been adopted as the interconnections between chips, which have the height of about 1/5 and the contact area only 1/25 of a flip-chip joint. Therefore, current density may reach 104 A/cm2 in microbumps, and electromigration (EM) can be a very important reliability issue. Due to the small amount of solder, the EM behavior is expected to be quite different from that in traditional flip-chip solder joints with bump heights of 70-100μm . In this three-year project, we will fabricate the EM test structures of 40-μm-pitch microbumps and investigate the EM behavior of microbumps. In the first year, we will design the EM layout and fabricate microbumps by a packaging house. In the same time, we will study the EM behavior in traditional flip-chip solder bumps with bump heights ranging from 5 to 20 μm, which are very close to the bump height of microbumps. In the second and third year, we will investigate EM and thermomigration (TM) behaviors of the low-bump-height flip-chip joints and the microbumps. This project will bring critical advancement in understanding EM and TM behaviors in microbumps for 3D IC packaging.