Photolithography is a technique in which a substrate is covered with a film of a photopatternable composition, which is a radiation-sensitive material. The film is selectively exposed to radiation, i.e., some portions of the film are exposed to the radiation while other portions remain unexposed. Selectively exposing the film may be performed by placing a photomask between the radiation source and the film. The photomask may be a radiation-transparent material having radiation-opaque patterns formed thereon. In positive resist photolithography, the exposed portions of the film are removed and the unexposed portions are left on the substrate. In negative resist photolithography, the unexposed portions of the film are removed and the exposed portions are left on the substrate.
Negative resist photolithography may be used to prepare photopatterned silicones that hold great promise for functioning as stress buffer layers, redistribution layers, dielectrics and solder masks for electronics applications such as MEMS, bioelectronics, display and integrated circuit (IC) packaging applications. These patterned silicones may be prepared by processes such as photolithography. Unfortunately, to date patterned silicones suffer from the drawback of not having a technique for removing the patterned silicone film if an error has occurred in the film deposition and patterning process. The process of removing a patterned film is called “rework”, and it allows the patterned film with the error to be removed from the substrate surface so that the substrate can be recycled rather than be discarded.
Furthermore, silicones have been excluded from other electronics applications where removal of the silicone is a necessary or desirable feature for device builds. A technique to remove the silicone after patterning is needed for entry into markets such as negative photoresists.