Aspect ratios, sizes, and etch rates in photostructurable glass-ceramic

Photostructurable glass-ceramics (PSGCs), although not yet widely used, are well suited to many micro-optical and micromechanical applications. Their appeal stems from the combination of the physical properties of glass-ceramics with the excellent three-dimensional shaping control that can be achieved by laser-patterning a transparent photostructurable material. The PSGCs are both mechanically and thermally robust. Exposure with a focused 355-nm pulsed laser beam initiates a cascade of reactions that ends in crystallization of a different phase of the glass-ceramic. The crystal-rich phase etches chemically much faster than the original crystal-free phase. In this experiment, we examined the dependence of the chemical etch rate on the aspect ratios and sizes of structures made from Foturan, a commercially available PSGC. We fabricated several types of test structures in 1-mm-thick Foturan samples. We tested the initial and long-term etch behavior of Foturan etched in 5% HF as a function of the size of the etched structure. An aspect ratio of 100 for a 10-μm-wide trench etched through a 1000-μm-thick sample was achieved.