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 $Topas®$ is demonstrated. $Topas®$ 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-chip applications. 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 properties of $Topas®$ are measured and the zero shear rate viscosity is found to be $2.16×104 Pa s$ at 170 °C and $3.6×103 Pa s$ 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 oxygen plasma, 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 on top of a $Topas®$ film patterned by NIL is demonstrated. This exploits the chemical resistance of $Topas®$ 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.