Demonstration and Electrical Performance of Cu–Cu Bonding at 150 °C With Pd Passivation

In this paper, one low-temperature direct Cu bonding structure is demonstrated using metal passivated layers. With the protection of Cu bonding layer, the bonding temperature can be reduced to meet low thermal budget requirement. Direct wafer-level Cu bond scheme with Pd passivation is successfully demonstrated at 150°C. Electrical performance along with the material analysis and reliability tests of passivated Cu bonded structures is presented. Furthermore, reliability assessments, including current stressing, temperature cycling, and unbiased highly accelerated stress test, imply excellent stability without electrical degradation. Diffusion behavior between passivation Pd and Cu layers is surveyed, and the corresponding mechanism is discussed as well. The low-temperature Cu/Pd-Pd/Cu bonded structure presents good bond quality and electrical performance, indicating a great potential for 3-D integration applications.