Effects of argon plasma pretreatment of Si wafers on Si-Si bonding based on Mo/Au interlayers

To improve the bonding quality of Si-Si wafers bonded based on Mo/Au intermediate layers at room temperature, the surfaces of Si wafers were pretreated with argon plasma, and the effect of argon plasma pretreatment on Si-Si wafer bonding was analyzed by combining experimental and theoretical methods. Owing to the plasma treatment of Si wafers, the surface roughness of Si wafers was significantly reduced, and the bonded Si-Si samples had lower interfacial voidage. The average bonding strength of 11.46 MPa for the argon plasma pretreated Si-Si bonded samples is much higher than the bonding strength of 4.23 MPa for the unpretreated Si-Si bonded samples. The analysis of the fractured surface revealed that the fracture of the Si-Si bonded samples without argon plasma treatment occurred mainly at the Mo/Si interface, while the fracture of the plasma-treated Si-Si bonded samples arose mainly within the bulk Si. Molecular dynamics (MD) simulations suggest that strong atomic diffusion takes place at the Mo/Au interface, while Mo atoms hardly diffuse into the bulk Si. These results indicate that argon plasma pretreatment not only cleans and activates the Si wafer surface but also makes the Si wafer surface smooth, which helps to enhance the deposited Mo/Au film quality and the adhesion between the Mo film and the Si wafer.