Patent ID: 8716123

Claim:
A method of forming an integrated circuit device, comprising: forming an under-bump-metallurgy (UBM) layer overlying a semiconductor substrate; forming a first photoresist film on the UBM layer, the first photoresist film having a first photosensitivity and a first thickness, forming a second photoresist film on the first photoresist film, the second photoresist film having a second photosensitivity and a second thickness, wherein the first photosensitivity is greater than the second photosensitivity and the second thickness is greater than the first thickness; performing an exposure process on the second photoresist film and the first photoresist film; removing an exposed portion of the second photoresist film to form a first opening; removing an exposed portion of the first photoresist film to expose a portion of the UBM layer and form a second opening underlying the first opening and a third opening underlying the second opening; wherein the second opening surrounded by the first photoresist film has a top diameter and a bottom diameter greater than the top diameter; forming a copper layer in the first opening, the second opening and the third opening, electrically connected to the exposed portion of the UBM layer; and removing the second photoresist film and the first photoresist film, wherein the copper layer forms a copper post.