The present disclosure relates to a method of forming a masking structure having a trench with a high aspect ratio, and an associated structure. In some embodiments, the method is performed by forming a first material over a substrate. The first material is selectively etched and a second material is formed onto the substrate at a position abutting sidewalls of the first material, resulting in a pillar of sacrificial material surrounded by a masking material. The pillar of sacrificial material is removed, resulting in a masking layer having a trench that extends into the masking material. Using the pillar of sacrificial material during formation of the trench allows the trench to have a high aspect ratio. For example, the sacrificial material allows for a plurality of masking layers to be iteratively formed to have laterally aligned openings that collectively form a trench extending through the masking layers.