30μm尺度下銅鎳錫銀以及銅銅錫銀微凸塊冶金反應及電遷移議題之研究

Abstract

電子元件微縮化的趨勢下，焊錫體積不斷的縮小，在三維積體電路中中微凸塊已經廣泛的被用來連接各晶片，焊錫高度縮小至20微米甚至更低，在此情況之下微凸塊能很快的轉變成介金屬化合物之接點，因此介金屬化合物接點將更受到重視。 本實驗我們使用金屬墊層開口為30微米尺度大小之錫銀接點來做研究，我們使用兩種金屬墊層組合來做研究，分別為Cu/Sn2.5Ag/Ni/Cu以及Cu/Sn2.5Ag/Cu。實驗中主要是利用Cu/Ni系統來觀測銅晶片端金屬墊層之消耗，並與Cu/Cu系統作比較。我們將試片作260℃迴焊測試、150℃高溫儲存測試以及電流密度8x104 A/cm2電遷移測試，結果顯示在迴焊測試以及電遷移測試下Cu/Ni系統基板端鎳墊層的存在會使銅晶片端加速消耗，在高溫儲存測試之下卻是Cu/Cu之金屬墊層消耗較快，我們對於各階段的差異來做不同的解釋，並對於Cu/Ni系統中介金屬接點所需要之銅金屬墊層厚度作進一步之計算。

With intent to satisfy the demand of smaller electric component, the volume of solder continue shrinking. In three-dimensional integrated circuit, the microbump has been adopted to be interconnections between chips. The bump height decrease to 20μm or even lower. In this condition, the solder joint may transform into fully intermetallic compounds (IMCs) joint during electromigration (EM). In this study, we use the SnAg solder bump samples with the dimension of 30μm in width. There are two kinds of under-bump-metallization (UBM) were used: one type is Cu/Sn2.5Ag/Ni/Cu and another is Cu/Sn2.5Ag/Cu. We study the metallurgical reactions at liquid state and solid state. The bumps in the liquid state were reflow at 260°C and the process in the solid state were annealed at 150°C in the oven. In addition, we also conducted EM test in our samples with the current density 8x104 A/cm2. In the reflow and EM process, Cu/Ni system has faster dissolution rate in Copper UBM side than Cu/Cu system. The present of Nickel UBM at the substrate side can facilitate the Copper diffusion from the chip side. The different outcomes have been found in the annealing process. We explain the reasons in each process and also calculate the critical thickness of Copper UBM used in the Cu/Ni system.