Chia Pay Ying, Haseeb A S M A, Mannan Samjid Hassan
Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia.
Physics Department, King's College London, Strand, London WC2R 2LS, UK.
Materials (Basel). 2016 May 31;9(6):430. doi: 10.3390/ma9060430.
Miniaturization of electronic devices has led to the development of 3D IC packages which require ultra-small-scale interconnections. Such small interconnects can be completely converted into Cu-Sn based intermetallic compounds (IMCs) after reflow. In an effort to improve IMC based interconnects, an attempt is made to add Ni to Cu-Sn-based IMCs. Multilayer interconnects consisting of stacks of Cu/Sn/Cu/Sn/Cu or Cu/Ni/Sn/Ni/Sn/Cu/Ni/Sn/Ni/Cu with Ni = 35 nm, 70 nm, and 150 nm were electrodeposited sequentially using copper pyrophosphate, tin methanesulfonic, and nickel Watts baths, respectively. These multilayer interconnects were investigated under room temperature aging conditions and for solid-liquid reactions, where the samples were subjected to 250 °C reflow for 60 s and also 300 °C for 3600 s. The progress of the reaction in the multilayers was monitored by using X-ray Diffraction, Scanning Electron Microscope, and Energy dispersive X-ray Spectroscopy. FIB-milled samples were also prepared for investigation under room temperature aging conditions. Results show that by inserting a 70 nanometres thick Ni layer between copper and tin, premature reaction between Cu and Sn at room temperature can be avoided. During short reflow, the addition of Ni suppresses formation of Cu₃Sn IMC. With increasing Ni thickness, Cu consumption is decreased and Ni starts acting as a barrier layer. On the other hand, during long reflow, two types of IMC were found in the Cu/Ni/Sn samples which are the (Cu,Ni)₆Sn₅ and (Cu,Ni)₃Sn, respectively. Details of the reaction sequence and mechanisms are discussed.
电子设备的小型化推动了3D集成电路封装的发展，这种封装需要超小规模的互连。这种小互连在回流后可完全转化为基于Cu-Sn的金属间化合物（IMC）。为了改进基于IMC的互连，人们尝试在Cu-Sn基IMC中添加Ni。分别使用焦磷酸铜、甲磺酸锡和瓦特镍镀液依次电沉积由Cu/Sn/Cu/Sn/Cu或Cu/Ni/Sn/Ni/Sn/Cu/Ni/Sn/Ni/Cu堆叠而成的多层互连，其中Ni的厚度分别为35 nm、70 nm和150 nm。对这些多层互连在室温老化条件下以及固液反应中进行了研究，样品在250℃下回流60 s，以及在300℃下回流3600 s。通过X射线衍射、扫描电子显微镜和能量色散X射线光谱法监测多层结构中反应的进程。还制备了聚焦离子束研磨的样品用于室温老化条件下的研究。结果表明，通过在铜和锡之间插入一层70纳米厚的镍层，可以避免铜和锡在室温下过早反应。在短时间回流过程中，添加镍抑制了Cu₃Sn IMC的形成。随着镍厚度的增加，铜的消耗减少，镍开始起到阻挡层的作用。另一方面，在长时间回流过程中，在Cu/Ni/Sn样品中发现了两种类型的IMC，分别是(Cu,Ni)₆Sn₅和(Cu,Ni)₃Sn。讨论了反应序列和机理的细节。
