The profile of the cone-shaped rods

The profile of the cone-shaped rods in the hybrid mask mold was inversely replicated to SU-8 resist
by the nanoimprint process. Due to the nature of the nanoimprint process, there is a thin layer of SU-8
residue at the bottom of the stamped trench, which must be removed by a subsequent O2 plasma etch
process. Since the rod profile is a cone shape, it is critical to control the O2 plasma etch time to get an
optimum etch profile in the SU-8 (Figure 7a). As the process time of O2 plasma etch increases, the
exposed window on the aluminum hard mask becomes larger. As shown in Figure 7b, for etching
times shorter than 21 s, results were not uniform and often gave irregular sizes and shapes of the
window opening on the aluminum hard mask. For relatively longer etch times (greater than 22 s),
fairly reproducible sizes and circular window openings were acquired.