Utilization of Direct Write Lithography to Develop Ultra High Aspect Ratio (>100:1) DRIE Silicon Pillars

Aspect ratios for deep reactive ion etching (DRIE) typically do not exceed 100. The discussed technique uses direct write lithography utilizing a Heidelberg DWL 66FS laser pattern generator followed by DRIE and hydrofluoric acid etching to create a nano pillar array on a silicon wafer. Prior to the direct write process, chrome was patterned on the wafer to act as an etch stop once the positive photoresist was consumed via DRIE. The sample was then oxygen-plasma etched to remove any remaining C4F8 residuals, as confirmed by Energy Dispersive X-ray spectroscopy. Remaining oxides were removed with dilute hydrofluoric acid and the wafer was rinsed with de-ionized water. The resulting structure was a nano pillar array with aspect ratios of 129.9:1, where pillar lengths were 50 μm with widths of 380 nm.