转印IMC诱发多层金属/Sn亚微米薄膜制备“单种IMC”焊点机理研究

In this project, IMC thin film with special crystal orientation and grain size will be transferred to the surface of metal/Sn submicron multilayer by laser irradiation, and then grain characters of the IMC film will be utilized to induce fast transformation of the metal/Sn submicron multilayer to a part of a joint. The joint is completely composed of one kind of IMC, and the crystal orientation of IMC transformed from the metal/Sn submicron multilayer will match well with that of the IMC film, and the joint is named as “Single IMC” micro joint. Investigation of Mechanism of crystal orientation and grain size control for the IMC film，thermal-force control in the process of laser transfer IMC film, and interaction between the IMC film with inducing effect and the metal/Sn submicron multilayer are key factors in realizing fast fabrication of “Single IMC” micro joints and control the microstructure of the joints. In addition, study on micromechanical behavior of the joints is the foundation for understanding the reliability issues of the joints. In this study, we will utilize micro-shear or in situ tensile technology to investigate micro-crack initiation, extension, and failure behaviors in the “Single IMC” joints from micro perspective (grain boundary, dislocation and vacancy motion of the IMC film, and the IMC induced by the film and transformed from metal/Sn submicron multilayer). The results will provide the most fundamental data for developing micro joints with high temperature stability and reliability.

本课题拟通过激光转印方法将预先制备的具有特定晶粒取向、尺寸的金属间化合物(IMC-Intermetallic Compounds)薄膜转移至多层金属/Sn亚微米薄膜表面，利用IMC薄膜诱导金属/Sn多层亚微米薄膜结构快速形成与IMC薄膜晶粒取向匹配的焊点，并由一种IMC所构成，即“单种IMC”焊点。IMC诱导薄膜晶粒取向及尺寸的控制机理、激光转印IMC薄膜过程中的热-力作用、IMC诱导薄膜与金属/Sn多层亚微米薄膜界面反应及机理研究是实现“单种IMC”焊点快速制备及其微观组织结构控制的关键，也是本研究的重点。而焊点微观力学行为的研究是理解其可靠性问题的基础。本研究将在微剪切或原位拉伸条件下，从IMC薄膜和其诱发的由多层金属/Sn亚微米薄膜演变而成IMC的晶界、位错和空位运动角度研究“单种IMC”焊点内微裂纹萌生、扩展和失效等行为，为开发具有高温稳定性及可靠性的微互连焊点得到最基础的数据。

本课题通过激光转印方法将预先制备的具有特定晶粒取向、尺寸的金属间化合物(IMC-Intermetallic Compounds)薄膜转移至多层金属/Sn亚微米薄膜表面，利用IMC薄膜诱导金属/Sn多层亚微米薄膜结构快速形成与IMC薄膜晶粒取向匹配的焊点，并由一种IMC所构成，即“单种IMC”焊点。研究发现：毫秒级激光转移IMC薄膜过程存在热扩散现象，沉积点尺寸大于激光光斑直径，且随着激光功率增大而增大，沉积点尺寸随着离焦值的增大先增大后减小。转移过程机理为：在激光能量输入较小时（在转移阈值附近），源基板上薄膜自由表面可能存在部分IMC来不及相变以固态沉积，沉积时气化推动力较小，薄膜成块状沉积，薄膜厚度分布较均匀。在激光能量输入较大时，气化现象加剧，中心区域气化推力较大，会将物质推向边缘沉积，形成“火山口”形沉积点，物质主要以熔化态转移到沉积点边缘，沉积点整体厚度分布不均匀。激光能量输入过大时，更多物质发生气化烧蚀，并在沉积过程中发生消失，最后只有极少物质发生沉积。诱发薄膜在诱发过程中，晶粒尺寸越大的诱发薄膜所诱发出来的新晶粒晶粒尺寸也越大。与之不同的是晶粒取向差角，无论诱发基板取向差角如何分布，诱发过程中都会发生取向差角向60°角集中。这种取向差角的集中是因为Cu/Cu3Sn存在特定的位向关系。诱发结果中出现长条晶粒包裹近等轴晶粒的原因在于相邻Cu3Sn晶粒在吞并同一个Cu6Sn5晶粒时速度差异过大，导致吞并速度小的Cu3Sn晶粒逐渐被吞并速度大的Cu3Sn晶粒所包裹。为了减小错配度，IMC和基板之间会尽量形成位向关系，而Cu3Sn的(100)晶面是其所有晶面中原子密度最接近Cu基板晶面原子密度的，故（100）晶面基本平行Cu基板表面。在微剪切条件下研究了IMC薄膜和其诱发的由多层金属/Sn亚微米薄膜演变而成“单种IMC”焊点内微裂纹萌生、扩展和失效等行为，为开发具有高温稳定性及可靠性的微互连焊点得到最基础的数据。