A new technique to fabricate overhanging structure for forming IC metal patterns by lift-off

A new method is proposed to fabricate negative sidewall for forming metal patterns by lift-off in IC. It utilizes two layers of same optical positive resists. Two extra flood exposures are conducted, both layers with different times, which change the bottom resist to an etchable layer and make the upper layer carry the metal away much more easily. When the upper layer is developed, an overhanging structure can be formed by the undercontrolled overetch of the bottom layer. Compared with other methods, the new technique is simple and convenient to operate and easy to lift- off, It is especially practical to form some special metal patterns, such as Au, Pt, in some ICs.