METHODS OF FORMING BONDING STRUCTURES

A method includes forming a conductive pad over a substrate, forming a multi-layer passivation structure on the conducive pad, patterning a top portion of the multi-layer passivation structure to form a first opening, forming a mask film on sidewall surfaces of the patterned top portion of the multi-layer passivation structure, after the forming of the mask film, performing a first etching process to remove a portion of the multi-layer passivation structure directly under the first opening to form a second opening, after the performing of the first etching process, selectively removing the mask film, performing a second etching process to remove a portion of the multi-layer passivation structure directly under the second opening, thereby forming a third opening exposing the conductive pad, and forming a bonding structure in the third opening, where an etchant of the second etching process is different than an etchant of the first etching process.