Effect of high temperature storage on the stress and reliability of 3D stacked chip

In this work, the effect of high temperature storage (HTS) on the stress in and around Cu TSVs in 3D stacked chips is studied by scanning white beam x-ray microdiffraction. The x-ray microdiffraction measurements were conducted on different die levels in the stacked chips before and after HTS test. High resolution mappings of stress distribution were obtained and compared between pre-HTS and post-HTS for both the Cu via and the surrounding Si. The x-ray microdiffraction technique provides a means for nondestructive, direct stress measurement in a 3D die stack structure. Finite element analysis (FEA) was carried out for the test structure to interpret the measurement results and to discuss the thermal aging effect on the 3D chip. Overall, the results show reduced stress in both Cu and Si after HTS, which can be explained by stress relaxation occurred during HTS. The implication of the HTS results on long term reliability of 3D die stacks is discussed.