Embodiments of wafer bonding method and structures thereof are disclosed. The wafer bonding method can include performing a plasma activation treatment on a front surface of a first and a front surface of a second wafer; performing a silica sol treatment on the front surfaces of the first and the second wafers; performing a preliminary bonding process of the first and second wafer; and performing a heat treatment of the first and the second wafers to bond the front surface of the first wafer to the front surface of the second wafers.