Interface study for template release in step and flash imprint lithography
Step and Flash Imprint Lithography (SFIL) is an attractive method for patterning sub-100 nm geometries. SFIL uses photopolymerization of an imprint material by exposure with UV light through a rigid, transparent, imprint template to define the pattern on planar substrates, without projection optics or lenses required for photolithography. New template design and imprint material development introduce promising applications for ultra-large scale integrated (ULSI) circuit interconnect fabrication. In the SFIL process, a complete separation at the interface of the template and imprinted material is one of the key aspects to success. The goal of this work was to investigate various treatment methods and strategies to assist template release, improving imprint fidelity. A fluorinated, self-assembled monolayer (FSAM) was investigated as a release layer to lower the template surface energy. Hydration conditions on the template were demonstrated to be crucial to film quality during FSAM deposition from the vapor phase as confirmed by water contact angle, ellipsometry, XPS and AFM measurements. For indium-tin-oxide (ITO), which is a promising template material, use of an amine catalyst was necessary to successfully deposit a durable and dense FSAM coating. For multi-tier templates designed for a dual damascene process, a hydrocarbon release layer is preferred over FSAM release layers to eliminate voids in the imprinted material. Beyond the strategy of growing a release layer on templates to assist separation, addition of a surfactant to the imprint material as a way to lower interfacial energy was also studied. This strategy was demonstrated to be effective in reducing the separation force and interfacial adhesion energy. A model for prediction of the surfactant concentration profile and the surface tension of the imprinted material as a function of surfactant concentration was also developed.