Improvement of Thermal Conductivity of Electroplated Copper Interconnections by Controlling Their Crystallinity
Improvement of Thermal Conductivity of Electroplated Copper Interconnections by Controlling Their Crystallinity
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通过控制结晶度来提高电镀铜互连的热导率
DOI：
10.1115/ipack2015-48197
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
Ken Suzuki and Hideo Miura
中科院分区：
文献类型：
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作者：
Masaru Goto;Ken Suzuki and Hideo Miura
电镀铜薄膜对于先进电子产品中的互连是不可或缺的，例如TSV（硅通孔）结构、精细凸块以及各种器件和中介层中的薄膜互连。然而，据报道，与传统的块状铜相比，薄膜的电气和机械性能有很大差异。变化的主要原因可归因于薄膜中晶粒和晶界结晶度的波动。多孔或稀疏的晶界会导致电阻率增加和薄膜脆化。因此，根据维德曼-弗朗茨定律，电镀铜薄膜的导热率应根据其微观纹理而发生巨大变化。由于铜互连不仅用作电导体，而且用作热导体，因此阐明薄膜的结晶度和热性能之间的关系非常重要。在本研究中，通过实验研究了结晶度和物理性能的局部分布。由于沿互连的局部焦耳热导致温度分布，表明电镀铜薄膜中晶界质量的变化导致了电阻率的不均匀性，从而导致了薄膜中的焦耳热。在本研究中，研究了种子层材料对电镀铜薄膜热性能的影响。当在电镀铜薄膜和Ta扩散阻挡层之间沉积Ru籽晶层作为缓冲层时，由于铜和籽晶层金属之间的晶格失配减少，电镀铜膜中的结晶度和晶界均匀性均得到改善。结晶度的提高提高了互连在电迁移和应力诱导迁移负载下的长期可靠性。
Electroplated copper thin films are indispensable for the interconnections in the advanced electronic products, such as TSV (trough silicon via) structures, fine bumps, and thin-film interconnections in various devices and interposers. However, it has been reported that both electrical and mechanical properties of the films vary drastically comparing with those of conventional bulk copper. The main reason for the variation can be attributed to the fluctuation of the crystallinity of grains and grain boundaries in the films. Porous or sparse grain boundaries cause the increase in electrical resistivity and the embrittlement of the films. Thus, the thermal conductivity of the electroplated copper thin films should be varied drastically depending on their micro texture based on Wiedemann-Franz law. Since copper interconnections are used for not only electrical conductor but also thermal heat conductor, it is important to clarify the relationship between the crystallinity and thermal properties of the films.In this study, the local distributions of the crystallinity and physical properties were investigated experimentally. As the result of the temperature distribution due to local Joule heating along an interconnection, it was suggested that the variation in the quality of the grain boundaries in the electroplated copper thin-films caused the non-uniformity of the resistivity and thus, Joule heating in the thin films. In this study, the effect of the seed layer material on the thermal properties of the electroplated copper thin film was investigated. When a Ru seed layer was deposited as a buffer layer between the electroplated copper thin film and the Ta diffusion barrier layer, both the crystallinity and uniformity of grain boundaries in the electroplated copper films were improved since lattice mismatch between copper and the seed layer metal was decreased. The improvement of the crystallinity increased the long-term reliability of the interconnections under the loads of electromigration and stress-induced migration.