Formation of high aspect ratio fused silica nanowalls by fluorine-based deep reactive ion etching

Even though fused silica was considered as a good mold material for nanoimprint lithography due to the properties of UV-transparent and high strength, fabrication of high aspect ratio nanometer-scale mold was challenging. A fabrication process for 120 nm-wide fused silica ‘nano-walls’ with high aspect ratio has been developed by using fluorine-based deep reactive ion etching (DRIE). The optimum conditions of the DRIE process to result in anisotropic vertical sidewalls with high-aspect ratio and good etch rate control were demonstrated as a function of bias power, process pressure, and argon percentage of the gas mixture. One of the vast applications of this process is the fabrication of the mold for UV nanoimprint lithography (NIL). Due to the fact that the resist is cured using UV-light, it is critical that the mold is transparent. A thin aluminum layer is used as a conducting layer for e-beam lithography, then used as an etch mask for fused silica etch. In the presented study, the etch rate increases with higher bias power and lower gas pressure. The existence of Ar makes the vertical surface smoother.