Surface Tension Driven Flow in a Low Molecular Weight Photopolymerby Kim, Chae Bin; Zhou, Sunshine X.; Heilman, Drew L.; Janes, Dustin W.; Ellison, Christopher J.
Low molecular weight photopolymers are candidate materials for resists in Extreme Ultraviolet Lithography. The patterned chemical transformations used in photolithography generate a surface energy pattern that can induce flow in low molecular weight photopolymers via the Marangoni effect, due to their intrinsically higher translational mobility relative to larger polymers. To demonstrate this outcome, a low molecular weight photopolymer bearing acid-labile protecting groups was co-cast with a photo-acid generator and exposed through a contact mask. During a post-exposure bake above the film’s glass transition temperature, unexposed polymer flowed into deprotected regions since the deprotected polymers possess relatively higher surface tension compared to the unreacted polymers. After cooling, the film exhibited thickness variations of up to 90 nm, and the topographic profile reflected the mask pattern. An appreciation of this transport mechanism could be useful to those integrating low molecular weight photopolymers into lithographic process flows.