Fundamental Insights\ninto Copper-Epoxy Interfaces\nfor High-Frequency Chip-to-Chip Interconnects

Future processes and materials are needed to enable multichip\npackages\nwith chip-to-chip (C2C) data rates of 50 GB/s or higher. This presents\na fundamental challenge because of the skin effect, which exacerbates\nsignal transmission losses at high frequencies. Our results indicate\nthat smooth copper interconnects with relatively thin cuprous oxides\n(Cu<sub>2</sub>O, Cu<sup>I</sup>) and amine-functional silane adhesion\npromoters improve interfacial adhesion with epoxy dielectrics by nearly\nan order of magnitude. For the first time, we present X-ray photoelectron\nspectroscopy (XPS) and Raman spectroscopy evidence of Cu(I)–O–Si\nbond formation at silane-treated interfaces. Thus, relatively smooth\ninterconnects can benefit from reduced skin losses while maintaining\ntheir mechanical integrity and reliability. Failure mechanisms of\nCu interconnects with cuprous and cupric oxide (CuO, Cu<sup>II</sup>) are explored using scanning electron microscopy (SEM) and Auger\nelectron spectroscopy (AES). These results indicate that both cupric\noxides and relatively thick cuprous oxide interfaces lead to relatively\nweaker interfaces compared with thin cuprous oxides with adhesion\npromoters.