Solid-State Growth Kinetics of Compound Layers in Electroplated Cu-In Layer Systems

• Published in: 2024 IEEE 10th Electronics System-Integration Technology Conference (ESTC) pp. 1 - 7
• Main Authors: Bickel, Steffen, Panchenko, Juliana, Junghahnel, Manuela
• Format: Conference Proceeding
• Language: English
• Published: IEEE 11-09-2024
• Subjects: 3D integration; Bonding; Compounds; Electrochemical deposition; Grain boundaries; growth kinetics; Heating systems; indium; Kinetic theory; Liquids; low-temperature bonding; Nickel; Nonhomogeneous media; Packaging
• ISSN: 2687-9727
• DOI: 10.1109/ESTC60143.2024.10712038

Low-temperature bonding technologies for advanced packaging are of substantial interest since they may enable the integration of a wide variety of components into highly integrated electronic systems. Replacing Sn in fine-pitch interconnects with In presents a viable approach for reducing the required bonding temperature while still exploiting the distinct benefits of liquid interlayers for joint formation. The technological feasibility of Cu-In microbumps depends at first on the grade and scale of interfacial metallurgical reactions. The present study is the first one addressing the growth kinetics of Cu-In compounds in electroplated Cu-In thin films. The results show a homogeneous growth of CuIn 2 up to 80 °C with a layer thickening proportional to the cubic root of the reaction time. The growth behavior is thus mainly controlled by grain-boundary diffusion and associated with an activation energy of 44 kJ/mol. The derived growth model is valid for compound layer thicknesses up to approx. 4 µm, above which volume-diffusion controlled growth becomes the primary mechanism. For temperatures above 100 °C, Cu 11 In 9 predominantly grows in an inhomogeneous way, but the average layer thickening obeys a t 1/3 -law. The growth rates are heavily impacted by the temperature, which is reflected by an activation energy of 76 kJ/mol. The cross-sections of the prepared samples and the derived growth models give novel insights into the early-stage growth behavior and kinetics, respectively, of Cu-In-based compound layers. The derived data provide an essential basis for developing criteria of technological parameters for the formation of Cu-In based fine-pitch joints.