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Title: Micromachining of Transparent Dielectrics and Silicon using Nanosecond Pulsed Laser
Authors: , Tunzeel ur Rahman
Keywords: Physical Sciences
Issue Date: 2022
Publisher: University of Azad Jammu and Kashmir Muzaffarabad, Pakistan
Abstract: Laser micro-structuring and micro-machining of glasses and silicon have attracted increasing amount of interest due to its wide range of applications in the fields of optoelectronics, microelectronics, medicine and biology. The direct micro-machining of glass is troublesome due to week coupling of laser beam with it. Laser-induced plasma-assisted ablation (LIPAA) is a recently employed indirect method to fabricate micro-channels, micro heaters, microfluidic devices and micro-patterns on the variety of transparent hard materials. Clearly, the morphology of glass micro-structure should depend on the laser and sacrificial material parameters. The objective of this study was to investigate the influence of laser parameters, operating conditions and the type of sacrificial material on the morphology of the glass micro-structures fabricated using LIPAA technique. The micro-craters on soda-lime glass were fabricated by LIPAA using Nd: YAG laser and aluminum (Al) as sacrificial material. The objectives were to investigate the impact of laser fluence and target-to-substrate distance on the morphology of microcraters and relate the observed effects with the plasma parameters. The incident laser fluence was in the range of 27-870 J/cm2 and target-to-substrate distance was in the range of 0 to 600 μm. The most obvious finding that emerged from this study was that the variation of plasma parameters (electron temperature and density) and change in size (diameter and depth) of micro-craters as function of laser fluence are quite identical. The electron temperature and density were in the range of 6320-11450 K and 7.78×1016 -2.0×1017 cm-3 , respectively. The saturation in the size of micro-craters and plasma parameters at high fluence attributes to plasma shielding. Next, the micromachining of soda-lime glass by LIPAA via Nd: YAG laser using aluminum and tungsten targets was performed. The objective was to understand the role of sacrificial material plasma in the LIPAA process and explore its impact on the structure of xxvii micro-craters. The size of the glass micro-crater was observed to depend on the laser fluence for both Al and W plasmas. However, the size of glass micro-craters fabricated by Al plasma was much bigger than that of the W plasma. The findings of these experiments revealed that ablation yield of sacrificial target material and size of plasma plays a vital role in LIPAA based micromachining of transparent materials. The effect of cw laser irradiation on the micromachining of quartz by LIPAA was analyzed. Silicon was used as sacrificial material and the target-to-substrate distance was 20 µm. The most important outcome of this study was the significant enhancement in quartz ablation due to the cw laser. A linear increase in the diameter, depth and volume of the quartz microfeatures was observed with the fluence of cw laser in the range of 3.5-10.2 µJ/cm2 . The maximum increase in the diameter, depth, and volume of the microfeatures was 35±6.4%, 198±11.9%, and 443±48.8%, respectively. Quartz ablation enhancement due to cw laser irradiation attributes to the increase in the size of silicon craters. The micromachining of silicon using single and multiple nanosecond pulses for the range of laser fluence 62-122 J/cm2 revealed that the size of micro-craters increases with laser intensity and saturates at higher values. The estimated mass of ablated material was in the range of 0.27×10-9 -2.69×10-9 g/pulse for this fluence range. The numerical simulation was performed to generate time-based temperature profiles along with target depth. The comparison of estimated target temperature and onset melting/boiling time at various laser intensities with crater’s depth provided valuable insight and knowledge of the micromachining process. The laser parameters were optimized to test the capability of LIPAA to fabricated smooth micro-channels on the quartz surface using silicon as target material. In addition to xxviii laser intensity, the micro-channel’s morphology found to depend upon the laser scan speed, number of passes and gap distance. The optimum condition to fabricate high-quality (crack free and smooth) quartz micro-channels are 315.6 kW/cm2 laser power density, 1000 number of passes, 30-45 mm/s scanning speed and 30 µm gap distance.The results presented in this thesis provide a deeper insight of the LIPAA process, and are quite useful for laser micromachining fraternity.
Gov't Doc #: 26029
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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