Excimer laser micromachining of structures using SU-8 (original) (raw)
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Excimer-laser ablation and micro-patterning of ceramic Si 3 N 4
Applied Physics A: Materials Science & Processing, 1997
Excimer-laser ablation and micro-patterning of ceramic Si 3 N 4 has been investigated. The ablation threshold in air, Φ th , is around 0.3 ± 0.1 J/cm 2 with ArF-and 0.9 ± 0.2 J/cm 2 with KrF-laser radiation. With fluences Φ th < Φ ≤ 4 J/cm 2 the irradiated surface is either very flat or it exhibits a cone-type structure, depending on the number of laser pulses employed. With fluences of 5 to 10 J/cm 2 , the sample surface becomes very smooth, much smoother than the original mechanically polished surface. Pores, scratches, and cracks observed on the non-irradiated surface are absent within the illuminated area. In this regime, the ablation rates are typically 0.1 to 0.2 µm/pulse.
Fabrication of high-aspect-ratio microstructures using excimer laser
Optics and Lasers in Engineering, 2004
An excimer laser micromachining system is developed to study the ablation of high-aspectratio microstructures. The study examines the ablation efficiency, specifically, the impact of changing major laser operating parameters on the resulting microstructural shapes and morphology. The study focuses on glass, although results on silicon and aluminum are also included for comparison. In ablating grooved structures, the ablation depth has been observed to be linearly proportional to the operating parameters, such as the pulse number and fluence. The results specifically indicate that ablation at low fluence and high repetition rates tends to form a V-shaped cross-section or profile, while a U-shaped profile can be obtained at high fluence and low repetition rate. The ablation rate or ablated volume has then been quantified based on the ablation depth measured and the ablated profile observed. The threshold fluence has also been obtained by extrapolating experimental data of ablation rate. The extrapolation accuracy has been established by the good agreement between the extrapolated value and the one predicted by Beer's law. Moreover, a one-dimensional analytical solution has been adopted to predict the ablated volume so as to compare with the experimental data. The reasonable agreement between the two indicates that a simple analytical solution can be used for guiding or controlling further laser operations in ablating glass structures. Finally, the experimental results have shown that increasing the repetition rate favors the morphology of ablated surfaces, though the effect of repetition rate on ablation depth is insignificant. r
A quality study on the excimer laser micromachining of electro-thermal-compliant micro devices
Journal of Micromechanics and Microengineering, 2001
The objective of this research is to improve the quality of the KrF excimer laser micromachining of metal and silicon in fabricating electro-thermal-compliant (ETC) micro devices. The ETC devices combine the actuator and the mechanism into one monolithic compliant continuum and enable a range of mechanical manipulation tasks at micron scale. An efficient method for optimizing the process parameters in laser micromachining, using the orthogonal array-based experimental design method, is presented in this paper. The feed rate of the XY stage, the laser pulse frequency, the discharge voltage and the number of passes were used as the control parameters. The roughness of the machined edge was used as the primary indicator of cutting performance. The roughness of the edges was computed automatically from the optical image of the machined samples. The heat-affected zone, kerf width and rate of cutting depth (depth per one pass) were used as additional quality indicators. The orthogonal array method enabled the optimization of the control parameters by reducing the required number of experiments compared to the traditional full factorial experiment. Furthermore, machining in a liquid environment improved the quality and eliminated more debris and recast compared to machining in the air.
Fabrication of High-Aspect-Ratio Microstructures Using Excimer Lasers
An excimer laser micromachining system is developed to study the process in fabricating high-aspect-ratio microstructures. Specifically, the study experimentally examines process efficiency and the impact of changing major laser operating parameters on the resulting microstructural shapes and morphology. The materials considered in the study include glass, silicon, and aluminum. The ablation or micromachining rate has been observed to be strongly dependent on the operating parameters, such as the pulse fluence, number, and repetition rate. The results specifically indicate that ablation at low fluence and high repetition rate tends to form a V-shaped cavity, while a U-shaped cavity can be obtained at high fluence and low repetition rate. Additionally, the present study also indicates that a three-dimensional V-shaped cavity with large vertex angle can be formed by varying the focus depth of excimer laser. Materials of low thermal conductivity and low melting temperature are indeed more applicable to laser ablation.
Micromachining of TiNi shape memory alloy by excimer laser ablation
Device and Process Technologies for MEMS and Microelectronics II, 2001
In this paper we investigate excimer laser micromachining of TiNi shape memory alloy using an image projection system as an alternative to photolithographic patterning. We report on the characteristics of material removal by KrF excimer laser induced ablation at 248 nm and the dependence of material removal rates on laser parameters such as fluence and pulse frequency. Fluences at the workpiece using a 10× projection lens were up to 2.5 J cm -2 with pulse repetition rates up to 100 Hz. Conventional chrome-on-quartz masks were used for pattern transfer. Material removal mechanisms and rates of material removal are compared with those observed during excimer laser micromachining of polymers and ceramics and limitations on achievable lateral and depth resolution explored. Data obtained by a variety of characterisation methods are correlated to assess the effects of laser induced damage.
Projection ablation of glass-based single and arrayed microstructures using excimer laser
Optics and Laser Technology, 2005
Ablation of single and arrayed microstructures using an excimer laser is studied. The single feature microstructures are fabricated for evaluating the ablation mechanism, threshold fluence, and associated material removing (ablation) rate. The morphology changes during ablation are investigated with the focus on the formation of the ablation defects, debris or recast. The possibility of removing these defects is also evaluated and demonstrated. The present study concentrates on the borosilicate glass, although ablation of polyimide and silicon are performed and discussed for comparison. Polyimide and silicon are the most popular polymer or semiconductor material used in the electronics industry. The arrayed microstructures are ablated to demonstrate the fact that, by repetition of a simple-patterned mask associated with synchronized laser pulses and substrate movement, arrayed and more complex structures can be cost-effectively manufactured. The potential applications of these arrayed microstructures are discussed and illustrated. A low-cost replication technique that uses the arrayed microstructure presently machined as the forming mold for making electroforming nickel microneedles is specifically presented. Finally, the potential areas of using excimer laser in micromachining of glass-based structures for future research are also briefly covered. r
Design and performance of an excimer-laser based optical system for high precision microstructuring
Optics and Laser Technology, 1998
We report on the design of an excimer-laser based system for high precision micromachining of spinnerets using a mask imaging technique. Both the illumination and imaging unit are optimized for specified demagnification ratios of 5 and 15, respectively. Detailed investigations were performed to measure the resolution, depth of focus and the sensitivity for the position accuracy of the substrate depending on illumination parameters. A special test mask for measuring the resolution in combination with a new definition of measurement procedure is used. SEM views of ablation results with high machining quality are presented. ß
Laser micromachining for applications in thin film technology
Applied Surface Science, 2000
. Ž The patterning of thin and thick films 100 nm-2 mm is performed with excimer laser radiation l s 248 nm, t s 20 ns, 2 . s 5 Jrcm . The laser ablation is investigated for the film systems: Fe Co rSiO -multilayers, Tb Fe rFe Co max 0.6 0.4 2 0.4 0.6 0.5 0.5 multilayers and SiN -layers. The ablation process strongly depends on the film material, film thickness, as well as on the y laser parameters such as laser fluence and number of pulses. The influence of using a beam homogenizer on the ablation process is discussed. For applications in microsystem technology, the minimal attainable structure sizes and an appropriate choice of laser parameters are determined. The patterning of SiN -layers for application in solar cells is investigated. q 2000 y Elsevier Science B.V. All rights reserved.
Analysis of the formation and evolution of oriented microstructures on laser ablated silicon
Applied Physics A, 2008
A theoretical approach and qualitative analysis of the changes induced on the surface morphology and the formation of microstructures on silicon targets irradiated by excimer laser are presented. This study is based on theoretical principles of the laser ablation process, in particular, on the analysis of the contribution of the laser energy density, which involves the laser beam parameters and also the physical properties of the target material. For different laser incident angles, the formation of micro-columns oriented towards the laser incident direction is explained. Moreover, numerical simulations and ablation experiments carried out with an excimer laser corroborate the theoretical analysis.
Applied Surface Science, 2012
Throughout this investigation, experiments on laser ablation with silicon (Si) wafers have been performed using silicon nitride (Si 3 N 4 ) as a sacrificial layer to find the optimal fluence capable of removing the Si 3 N 4 , which allows the subsequent anisotropic etching in Si with potassium hydroxide. As a result, an alternative to the traditional micromachining techniques that require more steps and processing times has been introduced. The effect of the pulse numbers on Si wafers has been studied and it has been observed that when increasing the pulse numbers at the same fluence, the capacity of the pyramidal cavity formed was greater than using only one pulse at higher fluences.