An ion beam layer removal method of determining the residual stress in the as-fabricated TSV-Cu/TiW/SiO2/Si interface on a nanoscale

Abstract

Thermally induced residual stresses across the TSV-Cu/TiW/SiO2/Si interface in through‑silicon vias (TSVs) have raised serious concerns about mechanical and electrical reliability in 3D ICs. The lack of a nanometer-precision measurement technique for the TSV interfacial stress gradient makes the interface failure mechanism unclear. In this work, we propose an ion beam layer removal (ILR) method for determining the residual stress in the as-fabricated TSV-Cu/TiW/SiO2/Si interface on a nanoscale to facilitate identification of the failure mechanism of the TSV-Cu/TiW/SiO2/Si interface in as-fabricated TSVs. The measurement results showed that the residual stress fluctuates across the TSV-Cu/TiW/SiO2/Si interface and that both compressive stress and tensile stress existed within the interface system. Compressive stress occurred at all three interfaces, the TSV-Cu/TiW, TiW/SiO2, and SiO2/Si interfaces, but transitioned to tensile stress at a distance of 25–45 nm from these interfaces. The highest level of shear stress concentration appeared inside the TSV-Cu at a distance of approximately 45 nm from the TSV-Cu/TiW interface. This shear stress concentration explains the experimentally observed TSV interfacial cracking phenomenon.