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

Abstract

Laser-induced plasma ablation (LIPA) using a 248 nm KrF excimer laser was investigated for microchannel fabrication. Examination of the morphology in relation to ablation performance was emphasized, and a synthetic LIPA mechanism model was proposed based on the results. Backside LIPA with a metal target on the bottom can be attributed to a combination of two phenomena: laser-induced plasma vaporization thermal ablation from the metal target below and enhanced laser–glass direct interaction from the plasma residuum. The laser absorption enhancement of quartz substrate resulting from the metal residuum was validated clearly using absorption spectrum measurements. The influence of laser parameters on the etching quality during LIPA was also analyzed for processing optimization. Finally, fused quartz glass microchannels of outstanding surface quality and dimension uniformity were implemented. The channel depth was 28 μm, and the bottom surface roughness was better than several hundred nanometers.

High aspect ratio sapphire micromachining by ultraviolet laser‐induced plasma‐assisted ablation (LIPAA)

“…To further verify that the saturation in the engraving depth is not from an excess deposition from the out-ofreach target plasma, 11,25 a thin film of a target material can be deposited on the backside of the substrate. By pulsing the target with a low pulse overlap, a deposition of target material on the backside surface of the sapphire can be achieved without ablating the sapphire.…”

“…For the target to ablate, the laser fluence must be above the target material's ablation threshold but below that of the substrate 24 . Certain studies claim that the engraving depth is limited to the size of the plasma 11,25 . As the substrate and target material is consumed, the gap between the two increases and the substrate will be out of reach of the plasma.…”

“…Beyond the number of pulses required to attain this maximum engraving depth, a deposition of particles from the out‐of‐reach plasma occurs within the engraved feature. This deposition is said to obstruct subsequent pulses from reaching the target material which further deteriorates the surface quality 11,25 …”

“…24 Certain studies claim that the engraving depth is limited to the size of the plasma. 11,25 As the substrate and target material is consumed, the gap between the two increases and the substrate will be out of reach of the plasma. Beyond the number of pulses required to attain this maximum engraving depth, a deposition of particles from the out-of-reach plasma occurs within the engraved feature.…”

“…This deposition is said to obstruct subsequent pulses from reaching the target material which further deteriorates the surface quality. 11,25 The second mechanism is described as follows. The plasma generated from the target material deposits ions on the backside of the substrate.…”