Abstract
The ultra-precise machining (UPM) of surfaces with contact-free, beam-based technologies enables the development of flexible and reliable fabrication methods by non-vacuum processes for future application in advanced industrial fields. Laser machining by laser ablation features limitations for ultra-precise machining due to the depth precision, the surface morphology, and laser-induced defect formation. Contrary to physically-based etching, chemical-based dry and wet processing offer high quality, low damage material removal. In order to take advantage of both principles, a combined laser-plasma process is introduced. Ultra-short laser pulses are used to induce a free-standing microplasma in a CF4 gas atmosphere due to an optical breakdown. CF4 gas, with a pressure of 800–900 mbar, is ionized only near the focal point and reactive species are generated therein. Reactive species of the laser-induced microplasma can interact with the surface atoms of the target material forming volatile products. The release of these products is enhanced by the pulsed, laser-induced plasma resulting in material etching. In the present study, SiO2 surfaces were etched with reactive species of CF4 microplasma generated by their laser-induced break down with 775 nm pulses of an fs-laser (150 fs) at a repetition rate of 1 kHz. The dependency of the depth, the width, and the morphology of the etching pits were analysed systematically against the process parameters used. In particular, a linear increase of the etching depth up to 10 µm was achieved. The etched surface appears smooth without visible cracks, defects, or LIPSS (Laser-induced periodic surface structures).
Highlights
Ultra-precise surface machining (UPM) attracts increasing attention as enabling technologies for future developments in optics, microelectronics, and precision mechanics
The S iO2 surface was etched by the laserplasma and an etching pit was generated
In the present study, etching of SiO2 samples with reactive plasma generated by the laser-induced optical breakdown in CF4 at near atmospheric pressure was investigated
Summary
Ultra-precise surface machining (UPM) attracts increasing attention as enabling technologies for future developments in optics, microelectronics, and precision mechanics. The ideal properties of such surfaces are low roughness, high lateral and vertical dimensional precision, and low damage of the material near the surface. UPM is related to optical production where both etching processes and sophisticated polishing technologies are utilized for fabrication [1]. Modern system design calls for new approaches and technologies which enable local material processing that can be used for etching, deposition or modification of materials. New beam-based tools are required that enable innovative fabrication processes. Current examples are ion beam figuring and electron beam writing. These processes are limited in their flexibility as they require complex vacuum systems
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