Low temperature Si-to-Si wafer bonding with sol-gel coating as intermediate layer

In this study, Si-to-Si bonding process between two 4-inch, p-type silicon wafers has been successfully achieved with the assistance of tetraethylorthosilicate (TEOS) sol-gel coating. Atomic force microscopy (AFM) is used to measure the roughness of the sol-gel coating, and the contact angle of water on the sol-gel coated wafer is measured using an optical contact angle system. Fourier transform infrared spectroscopy (FTIR) is performed to determine the chemical bonds and bonding groups in the coatings. The bond strength is measured using an Instron tensile testing machine. The bond strength of up to 35 MPa has been achieved. The bonding mechanism for the low temperature sol-gel intermediate layer wafer bonding is found to be related to the surface smoothness, porous intermediate layer and high density of OH groups with small amount of absorbed water on the sol-gel coating.