A novel approach is presented to evaluate the mechanical stability of back end of line (BEoL) stacks. A SRAM test vehicle manufactured in 28 nm technology with copper pillar bumps is used. In a second step, the validity of the approach is also shown for a second sample manufactured in 22 nm technology and the experimental results are compared. To inflict damage to the BEoL stack of the respective semiconductor device, external forces are applied to the copper pillars (Cu-pillars) by shear loading using a tribo-indenter system. An acoustic emission (AE) detection sensor is attached to the sample to measure acoustic waves during the shear experiment as an indication for damage. The damage progression in the BEoL stack is extremely fast, hence details can't be resolved anymore with the piezo sensors of the tribo-indenter. However, due to the much higher temporal resolution, AE measurements give a more precise insight into the damage process. The resulting damages are imaged using nano X-ray computed tomography (nXCT) as well as scanning electron microscopy (SEM). The results provide a better understanding of the origin and the propagation of damages in the BEoL stack.

提出了一种新颖的方法来评估生产线后端（BEoL）堆栈的机械稳定性。使用28纳米技术制造的带有铜柱凸点的SRAM测试车。在第二步中，还显示了该方法对以22 nm技术制造的第二个样品的有效性，并比较了实验结果。为了对相应的半导体器件的BEoL堆叠造成损坏，使用摩擦压头系统通过剪切载荷将外力施加到铜柱（Cu柱）上。声发射（AE）检测传感器连接到样品，以在剪切实验期间测量声波，以指示损坏。BEoL堆栈中的损坏进度非常快，因此无法使用摩擦压头的压电传感器解决细节。然而，由于更高的时间分辨率，因此AE测量可以更准确地了解损坏过程。使用纳米X射线计算机断层扫描（nXCT）以及扫描电子显微镜（SEM）对造成的损坏进行成像。结果提供了对BEoL堆栈中损坏的起源和传播的更好理解。