Repairing Nanoimprint Mold Defects by Focused-Ion-Beam Etching and Deposition

Abstract

Nanoimprint lithography (NIL) has been attracting attention from many industries because of its potential use in producing various nanostructure applications through a simple, lowcost, and high-throughput process. There are three primary types of NIL: thermal (T-NIL), UV-NIL, and room-temperature (RT-NIL). T-NIL has a heating and cooling process because thermoset or thermoplastic resins are usually used as T-NIL resins. When a thermoset resin is used, the mold is pressed on a substrate coated with the resin at room-temperature. During pressing, the mold and substrate are heated to harden the thermoset resin, and after cooling, the mold is separated from the substrate. It is slightly different with thermoplastic resin: in this case, the mold is pressed on a substrate coated with the resin at the resin's glass-transition temperature (Tg). The mold and substrate temperatures are then decreased and the mold is removed from the substrate. Si, SiO2/Si, and Ni molds are usually used as T-NIL molds. UV-NIL is a room-temperature process because UV-curable resins are used as UV-NIL resins. The UV-NIL mold is pressed on the substrate coated with UV-curable resin and then the substrate is irradiated with 365-nm UV through the mold. After this irradiation, the mold is separated from the substrate. This means that UV transmissive material must be used as UV-NIL mold material. Generally, a quartz mold is used as a hard mold, and a polydimethylsiloxane (PDMS) mold is used as a soft mold. RT-NIL can be performed without heating, cooling, or UV irradiation. In this process, the sol-gel materials, such as hydrogen silsesquioxane (HSQ), spin-on-glass (SOG), and sol-gel indium tin oxide (ITO), are used as RT-NIL resins. This process requires high pressure, so Si or SiO2/Si molds are usually used. What type of mold to use is one of the most important factors in nanoimprint lithography because the mold must come into direct contact with the replication material and the imprinted pattern resolution depends on the mold pattern resolution. The pattern is therefore typically fabricated by electron beam (EB) lithography to obtain a high resolution pattern, thus necessitating a mold repair process with high resolution. In photolithography mask repair, focused ion beam (FIB) etching is used to remove Cr opaque defects, and FIB chemical vapour deposition (CVD), using hydrocarbon precursor gas, is used to repair clear defects. Two types of defect occur in NIL molds protrusion and hollow defects which correspond to the opaque and clear defects in photomasks. However, unlike photomask patterns, the NIL relief-structure patterns are formed on a substrate surface. Therefore, we