圆片级封装新型纳米孪晶铜重布线塑性应变机理与晶圆翘曲特性研究

Wafer level packaging (WLP) is a developing technology in advanced packaging. With the increase of integration of IC, a big challenge to this technology is faced with the question how to reduce the warpage effectively by means of the adoption of new metallization and new techniques. The proposed project focus on the fundamental problems at cutting–edge: Plastic deformation of Cu during WLP process and its influence on the warpage of Si wafer. It is proposed to replace the metallization of Cu in redistribution layer (RDL) with nano-twinned Cu(nt-Cu), which was shown superior thermal-mechanical properties in bulk materials, in order to effectively reduce the warpage generated during WLP process and to increase the reliability. By means of the research on electrodeposition with pulsed current, it is expected to realize a uniform and high density nt-Cu at wafer level. While by means of the observation of the evolution of microstructure of the redistributed metallization especially the microstructure of nt-Cu under different imposed external fields such as thermal, electronic and stress fields, it is intended to study the influence of ambient temperatures on the warpage of the WLP wafer. Together with the in-situ warpage measurement during WLP processing, it is intended to study the influence of some typical thermal impacts (e.g., curing and reflow) on the warpage mode as well as its characterization. Also by identifying the related parameters during thermal cycle, it is expected to establish the physical model between local strain and warpage, which would be beneficial to recognize the mechanism of the superior high stability of the nt-Cu and in turn beneficial to realize the optimal design of the processing parameters. All the effort would be greatly helpful for the development and enrichment of the theory and techniques for WLP.

圆片级封装（WLP）是近年来迅速发展的一种先进封装工艺。随着集成密度不断增加，所面临的严重挑战是如何通过材料和工艺来有效减小晶圆翘曲。本项目围绕WLP中铜塑性应变及其对晶圆翘曲的影响这一前沿基础问题，拟在WLP关键工艺之一的重布线金属中，引入热机械稳定性能优异的纳米孪晶铜，来缓解工艺过程导致的晶圆翘曲，提高WLP的可靠性。通过脉冲电镀工艺研究，在重布线中实现均匀的、高密度的纳米孪晶铜制备；通过观察重布线金属的微观组织尤其是孪晶的微结构在热、电、应力等多场耦合作用下的演化，研究纳米孪晶铜重布线在不同工艺温度下对晶圆翘曲的影响；结合先进的晶圆级翘曲原位测试，研究WLP的典型热过程（如固化和回流过程）中纳米孪晶铜重布线导致的晶圆翘曲特征和模式，从而提取相关参数，建立物理模型，揭示纳米孪晶铜热机械稳定性的机理，实现对工艺条件的优化设计，为WLP技术发展提供理论和技术储备。

项目按节点顺利完成，主要研究进展与成果如下：.①.通过对纳米孪晶铜制备方法的研究，掌握了圆片级制备高密度纳米孪晶铜的方法。在脉冲电镀法制备纳米孪晶铜的过程中，通过SEM观察的方法发现了孪晶生长规律，加深了对脉冲电镀实验条件下纳米孪晶的形核和生长过程的理解，为该工艺的工业应用提供了技术参考与储备。.②.通过晶圆Cu布线样品在多种热过程中的原位翘曲测试，阐明了铜布线层应力演化与圆片级封装中翘曲的相互关系，详细研究了铜布线层在热处理时的翘曲演变、应变松弛和塑性滞后特性。通过理论分析，对铜布线层在室温至400℃范围内的翘曲演变机理进行了总结。发现对铜布线层的室温翘曲影响最为明显的是其微结构和热处理时的最高加热温度。其他参数对铜布线层室温翘曲的影响十分有限。.③通过建立翘曲演变曲线和应变松弛速率之间的关系，采用拟合方法得到了在不同微结构的铜布线层中，应力和温度对晶圆翘曲演变的贡献，阐明了各样品晶圆翘曲演变曲线的成因。采用脉冲电镀制备的高密度纳米孪晶铜和甲基磺酸铜镀液制备的电镀铜布线层，铜布线层引入的翘曲可分别降低21%和35%。.④提供了一种能够根据需要调整铜布线层所致晶圆翘曲的方法，即低温冷却法。由于在低温冷却过程中，铜布线层内部也经历了弹塑性变形，当期恢复到室温之后，会有一部分塑性变形保留下来，从而能够降低布线层内部的拉应力，也能够有效降低晶圆翘曲。..通过该项目研究，对铜布线层引入的翘曲进行了系统研究，从而对圆片级封装中的翘曲问题有了更深刻的理解，建立了相应的物理模型；通过对潜在的新型圆片级封装布线材料――纳米孪晶铜的制备方法和热机械稳定性的机理的深入研究，加深了对脉冲电镀实验条件下纳米孪晶的形核和生长过程的理解，发现了纳米孪晶的生长规律。　期待今后相关研究成果若能应用于工业生产实践，有望实现圆片级封装工艺条件的进一步优化，将有效提升圆片级封装Cu/PI再布线（RDL）封装结构中Cu材料的制备和热处理工艺控制水平,　为集成电路圆片级封装（WLP）技术发展提供深入的理论基础和相关技术储备，为我国集成电路圆片级封装技术的发展做出更大贡献。