Effect of post exposure bake in inorganic electron beam resist and utilizing for nanoimprint mold

A high-aspect-ratio structural mold has been fabricated using a simple process that comprises of electron beam lithography (EBL) and post exposure bake (PEB) of inorganic resist. Using developed inorganic resist for mold, pattern transfer to a photo-curable polymer was carried out by ultraviolet nanoimprint lithography (UV-NIL). The developed inorganic resist has enough hardness to be used for mold because this resist structure is almost equivalent to that of quartz. The aspect ratio of the fabricated mold with PEB was 2.59; this value is twice the size of aspect ratio of fabricated mold without PEB (1.16). Thus, PEB is very effective in fabricating high-aspect ratio pattern in inorganic resist. The size of the fabricated mold with PEB was 1004 nm developed depth and 388 nm line and 252 nm space. Using the mold, UV-NIL was carried out. The size of replicated pattern was 942 nm height and 278 nm line and 241 nm space. The replicated height and line width were slightly smaller than mold depth and line width because of volume shrinkage of photo-curable polymer by UV irradiation. The aspect ratio of the replicated pattern using the mold with PEB was 3.39; thus, high-aspect-ratio transfer was also possible. This process is useful for rapid fabrication of quarter wavelength plates.