Copper-Epoxy Interface Engineering for High-Frequency Chip-to-Chip Interconnects

The reliability of high-frequency chip-to-chip (C2C) interconnects requires the durability of Cu interconnects and polymer dielectric interfaces. In this study, we examine the temperature cycling performance of Cu-epoxy interfaces, including methylimidazole and amine functional silane adhesion promoters along with electroplated or electroless metal interlayers such as Ni, NiCo_0.64P_0.25, NiW_0.48P_0.10, and CoW_0.66P_0.17. X-ray photoelectron spectroscopy is used to determine chemical states and compositions. O diffusion is analyzed using energy-dispersive X-ray spectroscopy. The adhesion strength was measured using a peel tester, and sheet resistance was characterized using a four-point probe before and after temperature cycle tests. Insertion losses were measured using a vector network analyzer as a function of temperature cycling. Our results indicate that organic adhesion promoters such as silanes show improvements in the initial adhesion; however, extended temperature cycling results in weakened interfaces associated with Cu oxidation. The CoW_0.66P_0.17 metallic interlayer is more durable and exhibits a minimal 0.02 dB mm^-1 change in insertion losses at 18 GHz after 1500 cycles.