倒装芯片上金属布线/凸点互连结构中原子的定向扩散

采用倒装芯片互连凸点串联回路研究了高温、高电流密度条件下倒装芯片上金属布线/凸点互连结构中原子的定向扩散现象，分析了互连结构中受电应力和化学势梯度作用的各相金属原子的扩散行为.在电迁移主导作用下，Ni(V)镀层中的Ni原子的快速扩散导致原本较为稳定的Ni(V)扩散阻挡层发生快速的界面反应，造成Al互连金属与焊料的直接接触.Al原子在电子风力作用下沿电子流方向向下迁移造成窗口附近焊料中Al原子含量逐步上升，同时，空位的反向迁移、聚集形成过饱和，导致Al互连中形成大面积空洞.焊料中的Sn，Pb原子在化学势梯度 关键词： 倒装芯片 凸点 电迁移 扩散

Directional diffusion of atoms in metal strips/bump interconnects of flip chip

The diffusion character of metal atoms in the interconnects of metal strips/solder bump was observed by series solder bumps on flip chip which were stressed by high density electric current under high temperature. Assumed that the diffusion of atoms was controlled by electrical stress and chemical potential gradient，the diffusion behavior of all metal atoms in interconnects was investigated. The Ni atoms in the Ni(V) finishes directionally diffuse along the electron flow and accelerate the interface reaction of Ni and Sn by electromigration. Thus the Ni(V) finishes lose the action of the diffusion barrier layer in turn that resulted in the direct connection of Al and the solder. The Al atoms migrate in the electron flow by the electron wind force induced the Al atoms content in solder near the passivation via increases with the stressed time. The vacancies move in the opposite direction with the Al atom flux，and collect in the Al strips. Then the voids appear after the supersaturation of vacancies. The Sn and Pb atoms in the solder diffuse along the concentration gradient because of the non-leading action of electromigration. The atoms in the solder driven by the chemical potential gradient and compression stress form the upward fluxes. The upward diffusion of solder erodes the Al strips，which made the Al strips failure due to the voids and corrosion. The Al and Sn/Pb atoms were driven by their respective dominant force，and result in durative mutual diffusion until the interconnects take place the open circuit because of the difference of mass flux.