Material effect on thermal stress of annular-trench-isolated through silicon via (TSV)

The material effect on the thermal stress of annular-trench-isolated (ATI) through silicon via (TSV) was investigated. The ATI TSV with two sets of materials as the Cu core with the BCB insulator and solder core with parylene-HT insulator were successfully fabricated. A lower stress level was observed for the ATI TSV with a solder core and parylene-HT insulator in experiments and finite element method (FEM) simulation. In order to reveal the origin of the lower stress, the ATI TSVs with different core materials were simulated. The Si ring with high Young's modulus and low CTE value blocked the effect of the different core material of ATI TSV inside the Si ring and maintained the stress in the Si substrate at the same level. The origin of the lower stress level in the Si substrate was determined to be the lower Young's modulus and CTE of insulator Parylene-HT than BCB. Due to the surrounding structure of the Si ring, the effect of different core material on thermal stress in the Si substrate became weak. The discussion of the material effect on the thermal stress of ATI TSV provided further understanding of the structure with the Si ring.