Development of Lift-off Photoresists with Unique Bottom Profile

Lift-off method for metal patterning has been widely used in the variety of electronic device fabrication processes such as semiconductor packaging, MEMS, and LED manufacturing. The big advantages of using lift-off method are the cost saving and the process simplification. However there is a serious issue that the deposited metal pattern has unexpected edge crown after photoresist stripping. In order to achieve desired metal patterns, two types of novel lift-off photoresist were developed, one is a single-layer negative tone photoresist and the other is a double-layer positive tone photoresist. After exposure and development processes, both the photoresists show unique and well-controlled "undercut" profile, which enables to form a targeted metal configuration after stripping. This paper reports the key parameter of photoresist and how to control the undercut profile.