Effects of Plating Current Density on Electrochemical Reliability of RDL: In-Situ Electrochemical Migration Testing and Time-to-Failure Prediction

초록

As semiconductor packages continue to advance toward higher integration densities, the reliability of the redistribution layer (RDL) has become increasingly critical. Scaling-driven reductions in dielectric spacing and linewidths can heighten susceptibility to dielectric failure modes, including time-dependent dielectric breakdown (TDDB). Among electrical reliability concerns, electrochemical migration (ECM) is widely recognized as a dominant failure mechanism, in which anodic copper dissolution and cathodic dendrite growth can lead to short-circuit failures. The kinetics of ECM are strongly dependent on copper grain size, which is in turn governed by the applied plating current density (ASD, A/dm2). In this study, the electrochemical properties of copper varying with ASD were characterized using linear polarization resistance (LPR) and potentiodynamic polarization (PDP). Furthermore, the moisture diffusivity of the photo-imageable dielectric (PID) under Biased Highly Accelerated Stress Test (B-HAST) conditions was evaluated via electrochemical impedance spectroscopy (EIS). The microstructural variations of copper induced by the applied ASD, particularly grain size, were analyzed using X-ray diffraction (XRD). B-HAST was conducted to validate the effect of microstructure characteristics-dependent electrochemical kinetics on reliability performance. Failure analysis using Focused Ion Beam (FIB) cross-sectioning was performed to verify the failure mechanism and dendrite morphology. Finally, incorporating these experimentally derived material parameters, a finite-element simulation model was developed to predict failure time, successfully establishing a comprehensive predictive model linking manufacturing process parameters to electrochemical reliability.

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