Drie of fused silica

This paper reports detailed characterization results of deep reactive ion etching of fused silica with three different masking materials: single-crystal Si, negative photoresist KMPR and SU-8. With an optimized etch recipe, KMPR and SU-8 show higher effective mask selectivity, are easier to integrate and remove than Si, making them better masks for creating high-aspect ratio features. Using a KMPR mask, a high aspect ratio (8:1) etch with a 6-μm mask opening is obtained. SU-8 masks also achieve high aspect ratios of 4.5:1 for 20-μm wide trenches, with mask selectivity of ~2:1. However the polymeric masks cause greater FS sidewall roughness.