Contamination-Free Cu/SiCN Hybrid Bonding Process Development for Sub- μm Pitch Devices with Enhanced Bonding Characteristics

Abstract

Hybrid bonding has emerged as a promising 3D integration technology for the next generation stacking devices with advantages of higher performance and smaller form factor. As for the future devices with fine-pitch (sub-μm level) copper (Cu) interconnects, however, there are critical issues to consider for a successful application of hybrid bonding processes; (1) Cu diffusion with scaled Cu pads and (2) Cu re-sputtering and chamber contamination during plasma surface activation step that lead to fatal device failure (e.g. electrical shorts) even with a small amount. Here, we demonstrated robust connections for 0.4 to 0.7 μm-sized Cu pads of fine-pitch with wafer-to-wafer (W2W) Cu/SiCN hybrid bonding scheme through N2 plasma development and present comprehensive analyses for surface activation process. A computational work carried out by reactive molecular dynamics (MD) simulations was employed to propose an optimal N2 plasma condition that can enhance SiCN-SiCN bonding characteristics. The optimized N2 plasma condition reproduces SiCN-SiCN bonding strength of above 2.0 J/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> while suppressing oxidation of Cu pads below 2 nm. Cu/SiCN hybrid bonding characteristics using N2 plasma were confirmed to be void-free, well Cu-Cu interdiffused, and mechanically well aligned from the assessment involving SAT, TEM/EDS and FIB-SEM/EBSD analyses. Moreover, our optimal plasma condition meets the contamination- free criteria indicating that it is a preferable surface activation scheme without contaminating the plasma chamber regardless of continuous operations. The methodologies demonstrated in this work suggest that hybrid bonding can be applied to future fine- pitch device applications for successful 3D integration.