Thermal stress analysis of all-copper interconnection in 3D IC
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摘要:
三维集成电路（Three-Dimensional Integrated Circuit,3D IC）技术相比于二维封装形式具有互连长度短、异构集成度高、功耗低以及封装尺寸小等特点. 因为铜基体具有优异的导电性、抗电迁移性和机械性能,全铜互联结构替代了焊球作为连接结构应用于3D IC中. 本文通过数值模拟研究了含有全铜互连和微流道结构的3D IC模型在循环温度载荷下的热可靠性,分析了全铜互联高度对模型内部热应力的影响. 结果表明,全铜互连部分的最大热应力与铜柱所处的空间位置相关,离模型中心越远,铜柱内的变形越大. 同时,最危险铜柱内部应力分布和变形情况表明,由于铜柱上下端面所受载荷性质不同,铜柱在热载荷作用下的Mises应力大致呈左右及上下对称分布. 这会导致铜柱的潜在失效模式是轴向压缩和剪切共同作用下的断裂或损伤. 另外,最大Mises应力随铜柱高度的增加而逐渐减小,当铜柱高度为300 μm时最大Mises应力趋于稳定,可以为全铜互连可靠性设计提供参考.
Abstract:Compared with the two-dimensional packaging, 3D IC (3D Integrated Circuit) technology has the characteristics of shorter interconnection length, better heterogeneous integration, lower power consumption and smaller package size. All-copper interconnection structures are used in 3D IC instead of solder balls because of the excellent electrical conductivity, electromigration resistance, and mechanical properties of copper matrix. In this paper, the thermal reliability of the 3D IC model with all-copper interconnection and micropin-fin structure is studied by numerical simulation, and the influence of the height of all-copper interconnection on the thermal stress inside the model is analyzed. The results show that the maximum thermal stress of the all-copper interconnection part is related to the spatial position of the copper pillar. The farther away from the center of the model, the greater the deformation in the copper pillar. At the same time, the internal stress distribution and deformation of the dangerous copper pillar show that due to the different nature of the load on the upper and lower end faces of the copper pillar, the Mises stress of the copper pillar under the action of thermal load is roughly symmetrically distributed left and right and up and down. This phenomenon can lead to a potential failure mode of the copper pillar that is fractured or damaged under axial compression and shear combined. In addition, the thermal stress gradually decreases with the increase of the copper pillar height, and the maximum thermal stress tends to be stable when the copper pillar height is 300 μm, which can provide a reference for the reliability design of all-copper interconnects.
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Key words:
- 3D IC /
- all-copper interconnection /
- thermal stress /
- finite element analysis
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图 5 不同网格数量下的铜柱最大Mises应力
Figure 5. The maximum Mises stress for different element number
图 9 铜柱的变形图（放大30倍）
Figure 9. Deformation of the copper pillar (has been magnified by 30 times)
图 10 危险点的应力与应变随时间变化趋势
Figure 10. The evolutions of stresses, and strains at the dangerous point
图 11 铜柱高度对最大Mises应力的影响
Figure 11. The maximum Mises stress plotted with the height of copper pillar
图 12 不同铜柱高度下铜柱上应力分布
Figure 12. The stress distribution on the copper pillar under different copper pillar heights
表 1 微针鳍流道和TSV结构的几何参数
Table 1. Geometry parameters of micropin-fin channel and TSV structure
参数 符号 数值/μm 微针鳍横向间距 ST 470 微针鳍纵向间距 SL 375 微针鳍高度 Hpf 230 微针鳍直径 Dpf 300 SiO2层厚度 TSiO2 1 TSV_Cu直径 DCu 22.5 微凸点高度 Hmb 28 微凸点厚度 Tmb 1 
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表 2 模型材料属性
Table 2. The material properties of the model
材料 密度/
（kg/m3）弹性模量/
GPa泊松比 热膨胀系数（×10−6/K） Si 2330 170 0.28 2.6 SiO2 2270 70 0.16 0.6 Cu 8900 70 0.35 17 FR-4 1850 22 0.35 17 聚氧乙烯 980 1 0.38 17
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