Analysis on the Adhesion Failure between Cu Metal Layer and Photosensitive Polyimide (PSPI) for 2.nD Re-Distribution Layer (RDL) Process

Abstract

The continuous scaling-down of semiconductor devices has improved the performance of devices, but various materials, processes, devices, and systems are being developed together for various functions and power reduction. In particular, technological advancements in the semiconductor packaging field have become more important recently. In order to connect many chips, there are various chip-to-chip connection methods in the 2.nD or 3D packaging field. When connecting these chips, research is needed to improve the adhesion issue between the existing copper (Cu) wiring and the build-up material in the interposer. This study evaluates adhesion failure between Cu metal layer and photosensitive polyimide (PSPI) for 2.nD redistribution layer (RDL), which is a core technology component for the advanced packaging technology scheme. By employing optimized plasma treatments using a mixture of Ar and O2 gas on the PSPI substrate, reduced Cu adhesion failure is confirmed by 90-degree peel-off mechanical test, contact angle analysis, atomic force microscopy (AFM), and x-ray photoelectron spectroscopy (XPS). It turns out that metal to carbon element bonding is critical parameter affecting this adhesion failure rather than surface roughness between metal and PSPI substrate. We also correlate this adhesion with the electrical parameters such as S-parameter and eye-diagram under different operating frequency conditions.