量測厚膜銅/鎳與銅金屬墊層的共晶錫鉛接點之電遷移活化能

Abstract

在元件無可避免的輕、薄、短、小化後，電遷移對於元件可靠度的影響已經是非常嚴重的議題，因此元件壽命變的難以估計，準確的計算活化能值就顯得其重要性。本研究設計並製造凱文結構來研究銅鎳墊層與銅墊層於共晶錫鉛銲錫接著下，其電遷移活化能的大小，在量測上，利用凱文結構來觀測銲錫凸塊在電遷移下電阻變化情形，並定義電遷移破壞準當其阻值上升至初始的1.2 倍。然而大部分的研究都定義當整個迴路開路時，為其破壞標準。測試條件為分別在140℃、150℃、160℃的加熱盤上施以0.9 安培，不同金屬墊層所造成的破壞機制將各別被討論，同時在銲錫凸塊中因焦耳熱效應所造成的溫升，將利用凱文結構與鋁導線電阻溫度係數來量測，此方式提供了一個比較好且方便的方法來探討銲錫凸塊電遷移測試下的焦耳熱效應。銅鎳與銅墊層在共晶錫鉛銲錫接著下，其量測到的電遷移活化能分別為1.52 與0.84 電子伏特。

Activation energy of electromigration is investigated in eutectic SnPb flip-chip solder joints with thick under-bump-metallizations (UBMs) of 5-μm Cu/3-μm Ni and 5-μm Cu. We fabricate the Kelvin probes to monitor the bump resistance during the current stressing, and define the electromigration failure as the bump resistance increase reaches 20% of its initial value. Most of the previous studies defined the failure of the electromigration when the stressing circuit was open. The current stressings were done on a hotplate with temperatures at 160oC, 150oC, and 140oC, and the applied current was 0.9 A. The failure mechanisms of different UBM structures are examined. The joule heating of the solder joints during electromigration test was measured by using Kelvin probes and aluminum Temperature coefficient resistivity effect. This approach provides a better way of studying joule heating due to electromigration test in flip chip solder joints. The activation energy was measured to be 1.52 and 0.84 eV for the eutectic SnPb solder joints with the Cu/Ni and Cu UBMs, respectively.