Electroless-Plated Gold Nanolayer for Low-Temperature Copper Hybrid Bonding

This study investigates the deposition and characterization of electroless-plated gold (Au) nanolayers for low-temperature copper (Cu) hybrid bonding applications. A 0.7μ m-thick thermally grown SiO₂ layer on 8-in Si wafers was coated with a 50 nm Ti adhesion layer and 1μ m Cu layer, followed by electroless Au plating to form ~7 nm nanolayers. Before plating, samples underwent wet pretreatment, and post-deposition analyses included X-ray photoelectron spectroscopy (XPS), grazing-incidence X-ray diffraction (GIXRD), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The electroless-plated Au exhibited predominantly metallic characteristics with minimal Cu oxidation and conformally covered the underlying Cu, achieving an average surface roughness (R_q) of 3.21 nm. Die bonding at 200° C and 15 MPa demonstrated successful Cu-Au interface formation, and shear strength of 14.9 MPa showed mechanical integrity. Furthermore, selective deposition of Au on patterned Cu pads surrounded by SiO₂ was achieved, and its potential as a cost-effective solution for metal nanolayer formation in Cu hybrid bonding technologies.