Nanoimprint lithography in the cyclic olefin copolymer, Topas, a highly ultraviolet-transparent and chemically resistant thermoplast

Thermal nanoimprint lithography (NIL) of the cyclic olefin copolymeric thermoplast Topas® isdemonstrated. Topas® is highly UV-transparent, has low water absorption, and is chemically resistant to hydrolysis, acids and organic polar solvents which makes it suitable for lab-on-a-chipapplications. In particular, Topas® is suitable for micro systems made for optical bio-detection since waveguides for UV-light can be made directly in Topas®. In this article full process sequences for spin coating Topas® onto 4 in. silicon wafers, NIL silicon stamp fabrication with micro and nanometer sized features, and the NIL process parameters are presented. The rheological propertiesof Topas® are measured and the zero shear rate viscosity is found to be 2.16x10⁴ Pa s at 170 °C and3.6x10³ Pa s at 200 °C while the dominant relaxation time is found to be 4.4 s and 0.9 s,respectively. The etch resistance of Topas® to two different reactive ion etch processes, an oxygenplasma, and an anisotropic silicon etch, is found to be 12.6 nm/s and 0.7 nm/s, respectively. The etch rates are compared to the similar etch rates of 950 k PMMA, cross-linked SU-8, and standard AZ5214E photoresist. Finally, UV-lithography (UVL) followed by metal deposition and lift-off ontop of a Topas® film patterned by NIL is demonstrated. This exploits the chemical resistance ofTopas® to sodium hydroxide and acetone. The demonstrated UVL and lift-off on top of an imprinted Topas® film opens new possibilities for post-NIL processing.