The Influence of Cu Pad Dimensions on the Thermal Expansion of Cu in Cu/SiO2 Hybrid Bonding

As Moore's Law approaches its physical limits, hybrid bonding has become essential in achieving high density interconnects for advanced semiconductor packaging. One of the key challenges in this process is ensuring sufficient thermal expansion of Cu pads to overcome surface recessions, or “dishing,” caused by chemical mechanical planarization (CMP). In this study, we examined the influence of Cu pad geometry, including Cu/SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> ratio, pad thickness, and bond pitch, on the thermal expansion behavior of Cu. Analytical solutions were developed to predict the vertical and triaxial expansion of Cu as a function of temperature, and the results were validated against finite element analysis (FEA) simulations. Our findings suggest that pad dimensions play a crucial role in predicting Cu-Cu contact, with thicker pads and higher Cu ratios exhibiting more significant protrusion. This work offers an efficient approach to estimating bonding temperature conditions without reliance on complex computational methods, providing valuable insights into the design of hybrid bonding systems.