Cu-Sn化合物电流辅助定向生长与微焊点瞬态键合机理

发布时间：2018-04-25 14:08

本文选题：电流辅助 + 固-液电迁移　；参考：《哈尔滨工业大学》2017年博士论文

【摘要】：信息、能源、空间探测等领域不断要求功能更强、尺寸更小、可靠性更高的微电子器件。三维(3D)封装技术作为新一代信息技术产业的重点发展领域,不仅使电子产品尺寸大幅度减少,性能大幅度提高,更使元件之间的互连长度从厘米级减少到亚微米级,相应的微互连方法也将发生革命性变化。在“低温连接、高温服役”的目标驱动下,全金属间化合物(IMCs)焊点实现3D封装叠层芯片互连引发高度关注,但传统的整体加热互连工艺,键合时间长、施加压力大等工艺特点为器件带来可靠性隐患。因此,如何快速、高效地制备可靠的全IMCs微焊点是3D封装叠层芯片互连技术中亟待解决的问题之一。本论文基于电流焦耳热效应和电迁移促进金属原子固-液互扩散的原理,通过施加104A/cm2量级的电流密度载荷,能够在毫秒级时间内实现IMCs定向生长的Cu-Sn微焊点键合,为3D封装叠层芯片互连提供了一种快速、高效的新连接方法。通过试验和理论分析相结合的方法,详尽地阐述了全Cu-Sn IMCs焊点电流辅助瞬态键合的相关机理、界面IMCs形貌演变规律、Cu/Sn界面固-液电迁移机制以及定向电流作用下Cu-Sn IMCs晶粒择优生长的原理,并对瞬态键合后微焊点的力学性能做出了评估。根据3D叠层芯片互连结构特点,分别设计了平行电极型和对接电极型两种电流辅助瞬态键合模式。在平行电极模式下,通过对键合压力、时间、电流密度载荷以及中间Sn钎料厚度等参数的优化,在0.16MPa、电流密度载荷1.5×104A/cm2条件下键合200ms后制备了无孔洞等缺陷的目标全Cu_3Sn焊点;同时,对接电极模式下基于对键合温度的调控,在不同电流密度载荷条件下键合180ms后制备了三种不同类型的全Cu-Sn IMCs焊点。利用选择性化学腐蚀的方法对电流辅助瞬态键合界面IMCs三维形貌微观组织进行分析发现:随键合时间的增加,固-液界面成分过冷程度加大,界面Cu_6Sn_5形貌将由胞状晶依次向胞状树枝晶、柱状树枝晶转变,当键合温度超过Cu_6Sn_5熔点,树枝晶Cu_6Sn_5熔化并演变为自由树枝晶的Cu_3Sn,最终Sn钎料消耗完毕形成全Cu_3Sn微焊点。MATLAB求解熔融钎料中Cu原子总量的计算结果表明,较高温度下的Cu原子固-液电迁移可以在毫秒量级时间内为生成全Cu_3Sn微焊点提供充足的Cu原子。该Cu_3Sn焊点织构具有高度的定向特征,在电流载荷下焊点中的Cu_3Sn晶粒均倾向于沿着[100]晶向择优生长,通过量子力学理论分析和投影面原子密度计算,证明Cu_3Sn的[100]方向为电阻较小路径。此外,剪切试验表明,焊点内部IMCs的形貌、物相种类、成分比将对力学性能影响显著,随着键合时间和电流载荷的增加剪切强度随之升高,定向生长的全Cu_3Sn焊点的剪切强度可以达到67.6MPa,约是键合初期Sn基焊点的2.3倍。在电流密度量级为102A/cm2、较低温度条件下的固-液电迁移试验表明,通电初期,固-液电迁移促进阳极一侧Cu_6Sn_5的生长,而抑制阴极一侧的生长,呈现明显的极性效应。随后的生长动力学分析表明,相比于界面反应中的晶界扩散和体扩散,Cu溶质原子的固-液电迁移在阳极Cu_6Sn_5的生长中起到主导作用,且阳极Cu_6Sn_5平均厚度与时间呈直线关系。同时,固-液电迁移外延生长的Cu_6Sn_5晶粒取向分析表明,生长初期的Cu_6Sn_5倾向于沿着电阻路径最小的[0001]方向择优生长,随着电流密度载荷的增加,Cu_6Sn_5沿着[0001]方向定向生长的趋势更加明显。
[Abstract]:In the fields of information, energy, space exploration and other fields, the more powerful, smaller and more reliable microelectronic devices are required. As the key development field of the new generation of information technology industry, three-dimensional (3D) packaging technology not only reduces the size of the electronic products greatly, improves the performance greatly, but also reduces the interconnection length of the components from the centimeter level. Less to sub micron level, the corresponding micro interconnect method will also revolutionize. Under the target of "low temperature connection, high temperature service", full metal intermetallic compound (IMCs) solder joint of 3D package laminated chip interconnects highly concerned, but the traditional integrated heating and interconnect technology, long bonding time, high pressure and so on are the characteristics of the process. Therefore, how to quickly and efficiently prepare the reliable full IMCs micro solder is one of the problems to be solved in the 3D package laminated chip interconnection technology. This paper is based on the principle of the Joule thermal effect and electromigration to promote the solid to liquid mutual diffusion of metal atoms. By applying the current density load in the order of 104A/cm2, the current density load can be applied. Cu-Sn micro solder joint bonding for IMCs directional growth in millisecond time provides a fast and efficient new connection method for 3D laminated chip interconnection. Through the combination of experimental and theoretical analysis, the related mechanism of transient bonding of the full Cu-Sn IMCs welding point current assisted transient bonding, the evolution law of the interface IMCs morphology, Cu/S The mechanism of solid liquid electromigration in n interface and the principle of preferential growth of Cu-Sn IMCs grains under the action of directional current are used to evaluate the mechanical properties of the micro solder joints after transient bonding. According to the characteristics of the interconnection structure of 3D laminated chips, two kinds of parallel electrode mode and butt electrode type are designed respectively. The parallel electrode mode is designed in parallel electrode mode. By optimizing the bonding pressure, time, current density load and the thickness of the intermediate Sn solder, the target all Cu_3Sn solder joint with no holes and other defects was prepared after bonding 200ms under the condition of 0.16MPa and current density load of 1.5 x 104A/cm2. At the same time, the joint electrode mode was based on the control of the bonding temperature in different current density loads. Three different types of all Cu-Sn IMCs solder joints were prepared after bonding with 180ms. By selective chemical etching, the microstructures of the three dimensional morphology of the transient bonding interface IMCs were analyzed by the method of selective chemical etching. It was found that the supercooling degree of the solid to liquid interface was increased with the increasing of bonding time, and the morphology of the interface Cu_6Sn_5 would be in turn from the cell crystal to the morphology. The dendritic crystal and columnar dendrite change, when the bonding temperature exceeds the Cu_6Sn_5 melting point, the dendrite Cu_6Sn_5 melts and evolves into the free dendrite Cu_3Sn. Finally, the calculation of the total Cu_3Sn micro solder joint.MATLAB to solve the total Cu atom in the molten solder of the Cu_3Sn micro solder.MATLAB shows that the Cu atom solid liquid electricity migration at the higher temperature can be at the higher temperature. In millisecond order of time, sufficient Cu atoms are provided for generating full Cu_3Sn micro solder. The Cu_3Sn solder joint texture has high directional characteristics. Under current load, the Cu_3Sn grains in the solder joints tend to grow along the [100] crystal. The [100] direction of Cu_3Sn is proved by the quantum mechanics theory analysis and the calculation of the projection surface's original density. In addition, the shear test shows that the morphology, phase type and composition ratio of IMCs in the solder joint will affect the mechanical properties significantly. With the increasing of the bonding time and current load, the shear strength of the all Cu_3Sn solder joint can reach 67.6MPa, which is about 2.3 times that of the bonding point at the early bonding of the Sn. The flow density is 102A/cm2, and the solid liquid electromigration test under the lower temperature shows that the solid to liquid electricity migration promotes the growth of the anode side Cu_6Sn_5, while the growth of the cathode side is inhibited. The subsequent growth kinetics analysis shows that Cu dissolves in the grain boundary diffusion and body diffusion in the interface reaction. The solid liquid electromigration of the mass atom plays a leading role in the growth of the anode Cu_6Sn_5, and the average thickness of the anode Cu_6Sn_5 has a linear relationship with the time. At the same time, the Cu_6Sn_5 grain orientation analysis of the growth of the solid liquid electromigration epitaxy indicates that the early growth of Cu_6Sn_5 tends to grow along the [0001] direction with the smallest resistance path, with the current of the growth. With the increase of density loading, the tendency of Cu_6Sn_5 to grow along [0001] direction is more obvious.

【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG40

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