Influence of Post-Bonding Annealing Treatment on Interface Characteristics of Si-Si Wafer Bonded via Room Temperature Surface Activation

In order to improve the bonding quality of Si-Si wafers, room temperature Si-Si surface-activated bonding based on Mo nano-interlayer and post-annealing treatment is executed, and the effect of the annealing temperature on the Si-Si interface characteristics is experimentally investigated. The experimental results show that with the annealing temperature increase of 100 to 500 °C, the percentage of the area covered by voids at the bonding interface of the bonded Si-Si wafers gradually decreases to zero at 300 °C and then remains unchanged till 500 °C. The average bonding strength reaches the maximum value of 6.57 MPa at 300 °C, exceeding that of bulk Si. The transmission electron microscopy analyses also demonstrate that the Si/Si bonding interface with a multilayer structure comprising amorphous 2.54 nm Si, 9.88 nm Mo and 3.79 nm Si is free of nanovoids. Moreover, the amorphous-state bonding interface partly turns into a crystalline-state interface after annealing at 500 °C. Furthermore, molecular dynamics simulations show that strong atomic diffusion occurs at the Mo/Mo interface under high-temperature annealing.