Lift-off photoresists for advanced IC packaging metal paternning

3D-TSV, 2.5D interposer, PoP and Flip-Chip wafer micro-bumping are being implemented for consumer electronic products such as mobile phones, tablets, and so on. The consumer product market trends toward smaller and thinner, and cause the IC packaging becoming more complexity. The lift-off method of the photoresist for IC packaging metal patterning has been widely used in the variety of electronic device fabrication processes such as MEMS, and LED manufacturing. The big advantages of using lift-off method are the cost saving and the process simplification. However there is a challenge that the morphology of the deposited metal pattern is difficult to be controlled. In order to achieve desired metal patterning, there are two types of novel lift-off photoresist were developed which are single-layer negative tone photoresist and double-layer positive tone photoresist. Both the photoresists show unique and well-controlled “undercut” profile which enables to form a targeted metal configuration after exposure, development and stripping process. This paper reports the key parameter of photoresist and shows how to control the undercut profile.