微电子封装用铜互连材料的制备、组织调控及可靠性

       集成电路系统发展迅速，电子封装结构逐渐趋于小型化，作为导电桥 梁的铜互连结构的特征尺寸随之减小，致使电子器件的可靠性问题越发显 著。然而铜微观组织与电镀图案尺寸的相关性研究却少有报道。此外，特 殊织构的新型铜互连材料，如具有（111）取向的纳米孪晶铜（NT-Cu）等 以其优异的电学性能，更是传统铜（Cu）材料非常有潜力的替代品。NTCu 作为互连材料与焊料界面的可靠性问题机理尚不明晰，仍需深入研究。 本研究通过控制电镀配方及工艺，深入研究了织构对 Cu/Sn 界面反应 的影响。首先，加速剂分子构型（碳链长度、巯基数量）及浓度会改变 Cu 膜内部晶粒的形状（等轴晶或柱状晶），择优取向为（111）或（220）。浓 度的增加使得界面柯肯达尔孔洞（Kirkendall void, KV）数量明显增多。对 于 NT-Cu 制备来说，孪晶促进剂的选择也对孪晶形态有一定的影响，但不 同促进剂所制备的孪晶组织对柯肯达尔孔洞均有抑制作用；而且当电流密 度从 20 mA/cm² 上升至 50 mA/cm² 时，老化实验后期界面 Cu₃Sn 层厚度明 显减小。此外，NT-Cu 和普通铜在 1.1×10⁴ A/cm²条件下的电迁移测试结果 表明，NT-Cu 具有更薄的 Cu₃Sn 层与更少的 KV，抗电迁移能力更强。 进一步地，在多种尺寸的焊盘、再布线及盲孔结构中制备了具有不同 织构的铜材料，研究了图形尺寸对铜材料组织及可靠性的影响。结果表明 随着图案尺寸的减小，材料的组织及轮廓均发生改变。具体地，当凸点焊 盘的直径由 40 μm 增加至 105 μm，等轴晶铜（EG-Cu）的平整性由 34.5% 降低至 23.5%，表现出强尺寸依赖效应。而对于孪晶铜而言，随着焊盘直径 增加，（111）织构由 9.6%增加至 38.1%；冷热冲击测试结果表明，随着铜 材料织构的改变，其失效也表现出不同的尺寸相关性，EG-Cu 主要集中在 小焊盘，而 NT-Cu 小焊盘的失效率较低。 本课题研究了添加剂、电流密度以及电镀工艺对铜材料微观组织的影 响，证明了铜互连材料内部微观组织调控可以提升可靠性，为实际互连结 构应用中铜材料的选择及优化提供参考，并为封装小型化趋势下可靠性的 提升提供了理论指导。

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