以無電電鍍技術沈積鎳/銅凸塊與銲錫和鎳銅之界面反應研究

Abstract

本實驗以無電電鍍(Electroless-plating)搭配微影成像及蝕刻技術，在氮化鋁基板上製作無電鍍鎳/銅雙層線路及凸塊；另藉由電鍍方法沉積錫鉛於無電鍍鎳/銅上，用以模擬鎳銅凸塊與銲錫球產生之界面反應，進而評估無電電鍍技術應用在覆晶構裝之可行性。X光繞射結果顯示，無電鍍鎳磷鍍層由非晶質及及微晶結構構成，而無電鍍銅則具有結晶結構，且在250℃下進行一小時退火處理對兩者之結晶型態沒有明顯改變。在氮化鋁基板上以蝕刻技術形成鎳金屬線路，再以微影成像技術定義出凸塊位置，進行無電鍍鎳15分鐘後去光阻後再無電鍍銅30鐘，可完成厚度約2 μm之無電鍍鎳/銅之雙層線路及高度約5 μm之鎳/銅凸塊結構。鎳/銅金屬與共晶錫鉛之界面反應分析顯示，介金屬化合物厚度會隨著250℃之熱處理時間增長而增加；但約在2小時後介金屬生長已趨緩，厚度不再有明顯變化，與鎳層具有相當之4 μm厚度；元素線掃描結果顯示，錫無法突破鎳層之阻絕，證實鎳層是一良好的擴散阻絕層；介金屬化合物由Ni3Sn4、Ni3Sn2及Cu6Sn5組成；當熱處理時間達12小時後，介金屬化合物內之鎳、銅元素多擴散至銲錫內部，顯示介金屬化合物慢慢轉變為Ni-Sn-Cu固溶體。

This work utilized the electroless plating technology, accompanying with the photolithography and etching processes, to prepare Ni/Cu double-layered metal bumps on AlN substrate. In addition, by depositing solder by electro-plating on Ni/Cu to simulate the interfacial reaction of Ni/Cu metal bump and solder, we evaluated the feasibility of electroless plating technology to under bump metallization (UBM) for flip chip bonding. From X-ray diffraction analysis, the Ni-P film was consisted of amorphous and microcrystalline structure and the Cu film was polycrystalline. After annealing at 250 ℃ for 1 hour, both of the structures of Ni-P and Cu layers had no change. By forming Ni metal lines on AlN substrate within photolithography process, we were able to achieve the structure of 2μm thick Ni/Cu double layer metal lines and 5-μm-height metal bumps by using the electroless plating technique. From the scanning electron microscopy (SEM) observation, we found that the thickness of intermetallic compounds (IMCs) increased with the time of thermal treatment at 250 ℃. When the time exceeded 2 hours, the thickness of IMCs had no distinct raise. Both the IMCs and Ni film had the same thickness (4μm). From element linear scanning, we identified that the Ni-P film was a good diffusion barrier layer since Sn could not diffuse through the Ni-P layer. The IMCs were consisted of Ni3Sn4, Ni3Sn4 and Cu6Sn5, as revealed by XRD and EDS analyses. After thermal treatment for 12 hours, the IMCs gradually were replaced by Ni-Sn-Cu solid solution due to dissolution of Ni and Cu.