| 摘要: | 本論文探討兩種不同結構的電遷移研究，一種是覆晶凸塊的結構，另一個是錫微米線中添加不同成分的鎳與銅對之電遷移的影響。這兩個結構通入的電流密度值為104A/cm2。實驗溫度設定為155℃, 180℃與200℃。銲料為Sn.07Ni和Sn3Ni。我們發現這些微量銅添加會以銅原子之型態遷移至銲點介面而與錫原子生成Sn-Cu介金屬化合物。對於錫銲點中參雜微量的鎳，銅原子則會與錫鎳反應生成三元的Ni-Cu-Sn介金屬化合物。而對於純錫銲點，在陰極端的二元Cu-Sn介金屬化合物會因為電子流衝擊而溶入錫銲點中。反之，如前所述，含微量鎳的錫，在電遷移的效應下，三元的Ni-Cu-Sn介金屬化合物發現比二元的Cu-Sn介金屬化合物穩定。此外，我們也發現一個很有趣的現象，在陽極與陰極端，銅極與金屬化合物的界面有很多的孔洞(Kirkendall void)出現。從FIB的剖面分析，我們發現陽極端的孔洞比陰極端的孔洞嚴重。因此，隨著電流流動的方向不同會有兩種不同斷裂模式發生，在陽極端，斷裂模式發生在介金屬化合物與銅金屬墊層之間，在陰極端，另一個模式是發生在介金屬化合物與銲點之間。此外，我們也計算出在電遷移的效應下，Sn0.7Ni合金與Sn3Ni合金的活化能分別為0.85 eV / atom和1.132 eV / atom。Sn3Ni合金的銅消耗比Sn0.7Ni合金及比純錫(Q= 0.68 eV/ atom, 資料來自同學戈鈴)來得慢，主要有兩個原因: 第一個原因是(Cu1-yNiy)6Sn5此三元相有比較慢的生長速率且也是銅擴散的阻障層，除此之外，此(Cu1-yNiy)6Sn5在電遷移效應下也很穩定。第二個原因是從質量守恆定律，銅消耗的量等於銅溶入銲料內與銅與IMC化合物混合的總量。從生長速率的圖(Fig 5.2~5.5)，我們知道Sn3Ni合金的IMC化合物的厚度比Sn0.7Ni合金小，所以銅在Sn3Ni合金的消耗量比Sn0.7Ni合金慢。 在錫微米線添加不同銅與鎳含量的電致遷移效應研究中，環境溫度設定為室溫與60℃。我們發現電遷移的速率為Sn0.7Cu>Sn>Sn3Cu>Sn0.7Ni>Sn3Ni。Sn0.7Cu是所有合金裡面為較最嚴重的遷移速率是因為共晶組合之Sn0.7Cu有較高密度的晶界。我們可以發現堆積在陽極端而孔洞發生在陰極端。然而Sn(Ni)銲料比Sn(Cu)銲料可抑制錫的電遷移速率。我們發現由於Sn(Ni)銲料的grain size 很大，接近20μm，所以推論Sn(Ni)的grain boundary path比較少，因此可抑制電遷移。我們也可以藉由因電遷移效應所堆積的體積演算出擴散係數(D)與有效電遷移係數(Z*)的乘積值，DZ*。根據實驗結果，推算出來的DZ*值跟文獻值很接近。 The effect of Ni and Cu additive on electromigration(EM) in Sn solder joints and lines have been studied. Both EM test samples were stressed under the current density of 104 A/cm2. The electromigration behaviors in Sn0.7Ni solder joints were investigated at 155℃, 180℃, 200℃, respectively. We found that the Cu additives were transported to the anode side and formed Cu-Sn intermetallic compound. For Ni doped Sn solder joint, a thin layer of intermetallic compound (IMC) formed at the interface which was identified to be the Ni-Cu-Sn ternary compound phase. Under EM test, we found that for the pure Sn solder, the interfacial Cu-Sn compound layer at the cathode side will dissolve into Sn. However, for the Sn0.7Ni solder joint, remarkablely, we found that the Ni-Cu-Sn ternary compound layer is more stable than the Cu-Sn compound layer under EM test. Another intriguing finding is that a line of voids (Kirkendall voids) occurred at the interface between IMC and Cu pad. From the FIB examination, the Kirkendall voids, which at the anode side is more serious than that at the cathode side. Depending on the direction of electron flow, two cracking failure modes were observed. One is on the anode side, the cracking was occur at the IMC / Cu interface, the other is on the cathode side, the cracking was occur at the IMC / solder. Comparing the activation energy between Sn0.7Ni alloy (Q= 0.85 eV/ atom ) and Sn3Ni alloy (Q= 1.13 eV/ atom ), we know that, under the EM current stressing, the Sn3Ni has the highest activation energy than Sn0.7Ni, therefore the Cu consumption rate of Sn3Ni alloy is the slowest. The reason for Sn3Ni alloy has the slowest Cu dissolution rate than Sn0.7Ni than pure Sn (Q= 0.68 eV/ atom, reference data from Ellen Ge). The reason for the lower Cu consumption rate is mainly due to the formation of (Cu1-yNiy)6Sn5 can induced a lower Cu consumption rate[33]. The first reason is that (Cu1-yNiy)6Sn5 has a lower growth rate and is an effective diffusion barrier under the EM stressing. Otherwise, the (Cu1-yNiy)6Sn5 also is much stable under the EM stressing, as aforementioned. The second reason is that, from the growth kinetic of data for the IMC, as seen the Fig 5.2~5.5, we found that the thickness of IMC of Sn3Ni alloy is much smaller than the thickness of IMC of Sn0.7Ni alloy. Considering the mass balance of Cu, the amount of Cu consumed is equal to the amount of Cu dissolved into the solder, and incorporated with the IMC compounds. The formation IMC thickness of Sn3Ni alloy is less than the IMC thickness of Sn0.7Ni alloy, therefore, the Cu consumption rate in the Sn3Ni alloys is the slowest than in Sn0.7Ni and even in pure Sn under the EM current stressing. Using solder lines structure, we have studied the electromigration phenomenon on Sn (Cu) alloys and Sn (Ni) alloys lines, which are Sn, Sn0.7Cu, Sn3Cu, Sn0.7Ni, Sn3Ni. Two EM test temperature were at the room temperature and 60℃. The samples were stressed under the current density of 104 A/cm2. Mass accumulation near the anode and void nucleation near the cathode were observed during the current stressing. The electromigration rates of the above alloys were determined by knowing the extrusion where at the anode side. Our results show that the magnitude were Sn0.7Cu>Sn>Sn3Cu>Sn0.7Ni>Sn3Ni. We known that Sn0.7Ni alloy and Sn3Ni alloy shows much higher electromigration resistance than Sn (Cu) alloys. Furthermore, the grain boundary diffusion is known to be the main kinetic path of atomic transport in EM. From the Fig 5.12, we know that the Sn (Ni) alloy has a larger grain size than Sn (Cu) alloy, compare from the Table III, we know that the grain size of Sn (Cu) alloys just 3~10μm, however, the grain size of Sn (Ni) alloy is almost 20μm, it’s means that the Sn (Ni) alloy has the less grain boundary density and the electromigration’s diffusion path is decrease. Therefore, the Sn (Ni) alloys can retard the electromigration than the Sn(Cu) alloys. However, a more detail study is needed to verify this suggestion. Otherwise, we can estimate the accumulation region, the atomic flux driven by the electromigration can be calculated. Then the effective charge number and DZ* value of the different solder alloy lines were obtained. The DZ* values agree with the literature data. |
