With the downscaling of microelectronic devices, thermal gradients become increasingly important, making thermomigration (TM) an important mass transport mechanism. We use a combination of thermal simulations using finite element (FE) methods and a 1D physics-based TM model to characterise and design test structures to study thermomigration in Cu interconnects. As the test structure, in order to locally heat a section of the Cu interconnect, we propose to add a W-heater below a classical electromigration (EM) test structure. Using experimentally calibrated FE thermal models, we study the temperature distribution and temperature gradients along the Cu interconnects for various configurations of the test structure. Subsequently, the 1D TM model is used to identify locations where the tensile stress would reach a critical stress, σ_crit, which can lead to void nucleation induced by thermal gradients. By comparing different heater positions, we show that a higher thermal gradient is expected when the heater is positioned further away from the local heat sinks. Based on the outcome of the simulations, we propose a modified test structure where metal levels are inverted such that the Cu metal line is closer to the heater. Such structure shows a 4× increase in temperature gradient compared to the original structure, facilitating TM characterisation studies.

随着微电子器件的小型化，热梯度变得越来越重要，使热迁移 (TM) 成为重要的质量传输机制。我们结合使用有限元 (FE) 方法的热模拟和基于 1D 物理的 TM 模型来表征和设计测试结构，以研究铜互连中的热迁移。作为测试结构，为了局部加热铜互连的一部分，我们建议在经典电迁移 (EM) 测试结构下方添加一个 W 加热器。使用实验校准的 FE 热模型，我们研究了测试结构的各种配置沿 Cu 互连的温度分布和温度梯度。随后，一维 TM 模型用于识别拉伸应力将达到临界应力的位置，σ _crit，这可能导致由热梯度引起的空洞成核。通过比较不同的加热器位置，我们表明，当加热器远离局部散热器时，预计会有更高的热梯度。基于模拟的结果，我们提出了一种改进的测试结构，其中金属层被反转，使得铜金属线更靠近加热器。与原始结构相比，这种结构的温度梯度增加了 4 倍，有利于 TM 表征研究。