UV-laser ablation of fused silica mediated by solid coating absorption

Abstract

Micro patterning of fused silica by laser ablation is very challenging due to the lack of absorption in the whole spectral range from the deep UV to the near IR. Beside vacuum UV lasers emitting at 157 nm or femtosecond lasers inducing multi photon absorption, indirect methods utilizing external absorbers are applied. Established methods like LIBWE and LIPAA are applicable in a backside configuration, i.e. the laser beam has to pass the workpiece before inducing ablation at the backside. This causes restrictions concerning the shape of the workpiece, i.e. generally a flat front surface is necessary. We propose an indirect ablation method that can be applied for both, back side and front side processing. The fused silica substrate to be machined is coated with a UV-absorbing oxide film. This film is irradiated using an excimer laser leading to ablation of the film and, at sufficiently high fluence, to surface ablation of the fused silica substrate. The ablation depth in the silica can be controlled by the fluence in excess to the threshold. The remaining coating in the unexposed areas is removed afterwards by large area irradiation of the whole surface at a fluence above the threshold of film ablation, but below the threshold of substrate ablation.

Microchannel Fabrication in Fused Quartz by Backside Laser-Induced Plasma Ablation Using 248 nm KrF Excimer Laser

“…The etched depth of a single pulse reached 600 nm, and the roughness was as low as 2.2 nm [17]. Ihlemann et al presented the same scheme with a UV absorbing oxide film instead of a silver coating, and single-pulse ablation depths ranging from a few to 500 nm were obtained, with a surface roughness lower than 5 nm [18]. Chemical corrosion [19] or successive electroplating [20] were also employed in LIPA treatment for the fabrication of good-quality microchannels.…”