A Three-Dimensional Ultraviolet Curable Nanoimprint Lithography (3D UV-NIL)

This study investigates the use of ultraviolet nanoimprint lithography (UV-NIL) for patterning three dimensional (3D) structures. Generating the 3D structures is a challenging task especially on an insulating substrate such as quartz. The quartz transparent mold is essential for the UV-NIL process. The 3D profiles were created on the negative tone photoresist, Microresist ma-N2403 using a Raith-150 electron beam lithography (EBL) tool in a single step variable dose controlled exposure. The developed 3D resist profiles were subsequently utilised as the 3D masking layer. The 3D patterns were transferred into the quartz mold substrates by a single-step reactive ion etching (RIE). Surface roughness below 2 nm has been achieved when the RIE process pressure is lower than 6 mTorr. The replication of the 3D mold structure by using the UV-NIL technique requires a two-step imprint process. The master mold profile was replicated onto a Microresist Ormocomp US-S4 resist on the first imprint to become the soft mold. The cured Ormocomp soft mold, was subsequently used as a mold for replicating the 3D pattern structures on the Microresist mr-UVCur06 resist in the second imprint step to create a positive replica of the original mold. A test pattern of a 3D pyramid-shaped array with multilevel features was successfully replicated using this technique. This paper reviews our recent work on 3D UVNIL mold making and imprinting processes.