Controlled etching of silicate glasses by pulsed ultraviolet laser radiation

TLDR: In this article, the etch depth increases linearly with the number of pulses and the tolerance achieved is better than 5 μm, where the etched holes are well defined in outline.

Abstract: Fused glass which is used as an insulation layer in the electrical packaging of integrated circuits can be precisely patterned by etching with pulsed, ultraviolet laser radiation. The glass absorbs weakly at both 193 and 248 nm lines of the excimer laser. Etching by 193 nm pulses (∼20 ns FWHM) begins at a threshold fluence of 0.5 J/cm2 and rises to 1200 A/pulse at ∼2.5 J/cm2. The etch depth increases linearly with the number of pulses and the tolerance achieved is better than 5 μm. The etched holes are well‐defined in outline. Etching by 248 nm pulses has a threshold fluence of ∼1.2 J/cm2. The etched pattern is irregular and shows damage due to shattering that is well outside the irradiated area. The etch depth is difficult to control since the surface that is produced is uneven. The maximum etch depth per pulse that was realized was only 150 A. The etching by 193 nm laser pulses is believed to depend on the creation of color centers which strongly increases the absorption cross section.