Atomic Diffusion Bonding of Wafers in Air Using Ag-3at%Cu Films

Abstract

This study examined the atomic diffusion bonding (ADB) of wafers using 3at%Cu-Ag (20 nm) films in air and compared it to that using Ag films. The bonding wave was observed even with exposure times of the film surface to air t_exp up to 2.6 × 10⁵ s (72 h), which was significantly longer than using Ag films under the ADB process. A large bonding strength was obtained after post-bonding annealing at 100°C in the t_exp range up to 1 × 10⁴ s (3 h), and at 150°C up to 2.6 × 10⁵ s (72 h). Structural analyses revealed that Cu precipitated on the surface of Ag-Cu films during film deposition, which prevented the cohesion of the Ag-Cu film surfaces by film surface exposure to air and improved ADB performance.