Recent developments in micromachining of fused silica and quartz using excimer lasers

Abstract

The characteristics and abilities of excimer lasers for micromachining of fused silica and crystal quartz are reviewed and their applications for making high‐precision and high‐quality microstructures are studied. In addition to the direct ablation technique, two special techniques: laser‐induced backside wet etching and laser‐induced plasma‐assisted ablation, are included in the review. In addition to the basic principle and equipment set‐up, the fundamental processing parameters for each technique are presented and evaluated. The importance of utilizing these parameters for micromachining is illustrated by developing specific formula for each technique in guiding each machining step for making different curved and arrayed structures for various industrial applications. The machined geometries and surface morphologies are also examined. The pros and cons of each technique are then discussed. Finally, recommendations for future efforts for better micromachining the fused silica and quartz are presented. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Laser‐induced front side etching of fused silica with KrF excimer laser using thin chromium layers

“…A linear increase of the etching depth with the laser fluence was also found for the back side etching process 10, 19, 20. At the LIBWE process for fused silica with a laser radiation of 248 nm a higher ablation threshold Φ th at 0.23–0.43 J/cm 2 and an equal slope coefficient at 24–42 nm/(J/cm 2 ) was reported 21.…”

“…During the front side etching process, the laser beam is focused onto the absorber layer and during the back side etching the laser beam is directly guided through the fused silica to the absorber layer. Regarding the absorber material configuration back side etching can be classified into different methods: Laser‐induced back side wet etching (LIBWE) 7–10, laser‐induced plasma‐assisted ablation (LIPAA) 10, 11, laser etching at a surface‐adsorbed layer (LESAL) 12, 13 and laser‐induced dry etching (LIBDE) 14–16.…”

Improving copper plating adhesion on glass using laser machining techniques and areal surface texture parameters

“…A mathematical relationship between the ablation depth and pulse number can be expressed as follows [19]:…”

“…The ablation mechanism with different glasses depends strongly on the composition of the glass. For a krypton fluoride (KrF) excimer laser, photons with a wavelength of 248 nm have an energy of approximately 5 eV, which is sufficient to break chemical bonds, causing a sudden pressure increase within the absorption region and ejecting material in an explosive manner into vapour and particles [19]. Since excimer laser pulse durations are short, the interaction with the material occurs very rapidly, and the opportunity for thermal damage to the surrounding material is minimised.…”

Ablation of silicon suboxide thin layers

“…While ablation at 193 nm is possible at high fluences (in excess of 2 J/cm 2 ) the ablation rate is found to depend on the surface roughness and irradiation by multiple pulses can lead to crack formation [1]. Processing of fused silica at 157 nm (F 2 laser) has been performed by a number of groups and interesting applications have been demonstrated [2][3][4][5]. The experimental effort, however, is very high: beam lines have to be evacuated or purged to remove any absorbing oxygen and laser optics have to be all-reflective or made from expensive materials like calcium fluoride.…”