Effects of halogenated organic solvents on laser-induced backside wet etching of fused silica

Laser-induced backside wet etching of fused silica using a solution of pyrene dissolved in halogenated and non-halogenated solvents is presented. A significant influence of the solvent used on the etch rate and the etched surface appearance was ascertained. The etching of uniform and smooth surfaces with rates of similar to 0.1 nm/pulse for laser fluences below 500 mJ/cm(2) is observed only for halogenated solvents. Furthermore, reduced threshold fluences, only small incubation effects, and a constant etch rate in dependence on the pulse number were found. The experimental data suggest an additional etch process at low laser fluences characterized by the very low etch rate and the smooth etching observed only with halogen-containing solvents. The generation of halogen radicals/compounds close to the heated surface due to the decomposition of the solvent causing the attack of the surface seems the most probable mechanism.