微接點中因界面反應引發之體積收縮行為

Abstract

近年來半導體產業的發展逐漸落後於莫爾定律的預期，透過發展三維立體構裝 (3D IC) 技術以持續提供半導體產業發展的動能儼然成為各界共識。在眾多發展中的3D IC 封裝技術中，具微小銲料凸塊之晶片接合法是相當受到矚目的構裝方式。然而3D IC元件內之銲點尺寸非常微小，因此接點空間受限Space confinement所導致的界面反應特徵勢必與傳統銲點不同。本研究將針對此種微小接點因界面反應誘發之接點體積收縮(Volume Shrinkage)效應，進行理論分析與實驗量測。從理論分析中得知當Cu與Sn反應形成Cu6Sn5介金屬(Intermetallic Compound)會伴隨著5%理論體積收縮值，而Cu3Sn與Ni3Sn4反應則分別對應7.5%與11.3%收縮值。因此本實驗利用表面輪廓儀對Ni/Sn/Ni、Ni/Sn-Ag/Ni以及Cu/Sn/Cu於180℃熱處理下進行試片體積之監測，並以SEM觀測對應之微結構變化。最後結果顯示，接點中之體積收縮將可能誘發接點內應力以及結構缺陷，對接點強度將具有相當大的影響，本研究係首次以完整的實驗結果證明該效應的存在。

Imminent ending of Moore’s law is the most critical issue threatening the continuing development of semiconductor industry. The strategy of consensus in order to go beyond Moore’s law is through the Three-Dimensional Integrated Circuit (3D IC) architecture. Among many 3D IC integration schemes under development today, solder micro-bumping is a very promising one. Due to the extremely small size of solder joints in 3D IC packages, interfacial reaction features are quite different to that in the conventional solder joints. The space confinement behavior must be considered in the soldering reactions. In this proposal, data analysis and experimental implementation of the volume shrinkage induced by interfacial reaction in micro joints is investigated. Theoretically, there is a 5% shrinkage in volume to produce Cu6Sn5 from the reaction between Cu and Sn. The shrinkages for Cu3Sn and Ni3Sn4 are 7.5% and 11.3%, respectively. Consequently, micro joints would be in highly stressed states and prone to failure. Experimentally, stylus surface profilometer and SEM are carried out to measure the actual volume shrinkages and observe microstructure for Ni/Sn/Ni, Ni/Sn-Ag/Ni, and Cu/Sn/Cu sandwich structures during an isothermal aging at 180℃. The results show that the internal stress and the forming of voids in micro joints during solid state aging might induce potential reliability issues. It is the first time that the reaction induced volume shrinkage is experimentally measured in common solder system. Theoretical analysis and experimental evidence are presented in this proposal to illustrate these issues, and implications based on the findings will be also discussed.