(中国科学院 金属研究所，沈阳 110016)
摘 要: 应用第一原理方法研究通过元素掺杂来抑制SnBi无铅焊料中Bi的电迁移问题。在SnBi体系中掺杂Zn和Sb元素，通过用近弹性带方法计算掺杂体系中Bi元素的扩散能垒。结果表明：加入Sb之后，Bi的扩散能垒由原来的0.32 eV升高到0.46 eV，扩散激活能由原来的1.14 eV升高到1.18 eV；加入Zn后，Bi的扩散能垒由原来的0.32 eV升高到0.48 eV，扩散激活能由原来的1.14 eV升高到1.22 eV。由此可得，Zn和Sb的加入都能够提高Bi的扩散激活能，起到抑制扩散的作用。通过分析态密度可知：加入Zn和Sb后，体系中Sb与Bi的p态曲线几乎完全重合，比Sn与Bi的p态曲线重合度高很多，说明Sb和Bi的共价键作用很强，且比Sn-Bi的共价键作用强，从而增加Bi的扩散能垒。同样，Zn和Bi的p态曲线重合度也比Sn和Bi的曲线重合度高很多，表明Zn—Bi的共价键同样比Sn—Bi的共价键强，所以Zn的加入同样增加Bi的扩散能垒。总结说来，Sb和Zn的掺杂能够抑制SnBi焊料中Bi的电迁移。
关键字: 第一原理计算；电迁移；SnBi无铅焊料；元素掺杂
electromigration of Bi
（Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China）
Abstract:The first-principles calculations on the elemental doping in SnBi lead-free solders were performed, aiming to inhabit electromigration of Bi element during microelectronic packaging. Zn and Sb elements were theoretically added into SnBi system, and the diffusion barrier energy of Bi was calculated with nudged elastic band (NEB) methods. The results show that, after Sb doping, the diffusion barrier energy of Bi increases from 0.32 eV to 0.46 eV, and the diffusion activation energy of Bi increases from 1.14 eV to 1.18 eV. On the other hand, after Zn doping, the diffusion barrier energy of Bi increases from 0.32 eV to 0.48 eV, and the diffusion activation energy of Bi increases from 1.14 eV to 1.22 eV. Zn and Sb can inhabit the diffusion of Bi during electromigration. The density of states (DOS) analyses show that p-state curves of Sb and Bi almost completely overlap, which indicates that Sb and Bi has stronger covalent bonding than Sn-Bi, thereby increases the diffusion barrier energy of Bi. The calculated DOS of Zn and Bi is the same as that of Sb and Bi, which indicates that Zn—Bi also has stronger covalent bonding than Sn—Bi, hence, the addition of Zn also increases the barrier energy of Bi. In conclusion, Sb and Zn doping can inhibit Bi electromigration in SnBi solder.
Key words: first-principles calculation; electromigration; SnBi lead-free solder; elemental doping
