Fabrication of High-Aspect-Ratio Microstructures Using Excimer Lasers (original) (raw)
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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
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
Excimer laser machining for the fabrication of analogous microstructures
Applied Surface Science, 1996
Excimer laser ablation is normally used for micromachining of binary structures, for instance holes or cuts. We investigated new machining techniques for the fabrication of three-dimensional (3D) structures with analogous topology by excimer laser ablation: (i) line scan with a contour mask which correlates with the desired topology and (ii) gray scale mask projection. The structuring methods make use of the dependence of the machined depth (i) on the locally applied pulse quantity or (ii) on the energy density. The details of the methods, the process parameters and the resultant structure properties are discussed. Examples for the structuring of cylindrical and spherical microlenses and microarrays with dimensions in the micron range are given.
Recent developments on microablation of glass materials using excimer lasers
Optics and Lasers in Engineering, 2007
For many years, the development of effective laser machining techniques for making glass-based microcomponents and devices has been a critical factor in the birth of new photonic and biomedical microsystems. In this article, the characteristics and abilities of excimer lasers for micromachining of a wide range of glass materials are reviewed and studied. Following the introduction, the special features of excimer lasers are discussed. The typical micromachining system used for glass materials is presented. Then, the fundamental micromachining parameters and the associated morphologies of machined surfaces are evaluated. The approaches by controlling the ablation rate for making the curve surfaces are specifically formulated. Although a wide range of commercially available glasses is covered in this article, two types of the most widely used glasses, borosilicate glass and fused silica, are thoroughly examined to illustrate the complexity in micromachining the glass materials. The procedures to machine single, arrayed, curved microstructures are described. The utilizations of these procedures for making microneedles, optical waveguides, submicron grating, and microlenses are specifically demonstrated. Finally, recommendations for future efforts are presented. r
Excimer laser micromachining of structures using SU-8
Micromachining and Microfabrication Process Technology V, 1999
The ablation characteristics of the SU-8 photoresist (spun on Si wafers) under 248 KrF excimer pulsed laser radiation have been studied. The variation of etch rate with fluence has been investigated in the range 0.05-3.01 J cm −2 . The threshold fluence for ablation of SU-8 is measured to be about 0.05 J cm −2 . The etch rate of SU-8 is found to be higher than that of polyimide (previously reported) under similar conditions. We have investigated the effects of different prebake temperatures (90, 110, 120 and 200 • C) on ablation characteristics, which are found to be similar for all temperatures. The effect of increasing the number of laser shots (from 10 to 10 000) has been examined at different fluences in order to understand the etch-rate variation near the 'end of film' stage of ablation. The results of our analysis using scanning electron microscopy, profilometry and optical microscopy reveal the very smooth morphology of the etched surfaces with no significant debris, no noticeable damage to underlying silicon and the gradual build-up of a carbonaceous film outside and around the etch pits. We find SU-8 very suitable for excimer ablation lithography and have demonstrated this by patterning a gear structure in an SU-8 resist layer with an aspect ratio of 4.5. For the first time, we have shown that the laser micromachining technique has the potential to cleanly remove SU-8 after electroplating a microstructure with copper.
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.
SN Applied Sciences, 2020
This paper presents the process development and characterization towards microstructural realization using laser micromachining for MEMS. Laser micromachining technique is environmental friendly, fast patterning and able to avoid multi steps in conventional lithography based microfabrication techniques. This research focuses on understanding the dimensional properties of materials of the laser beam on the silicon wafers where microstructures were fabricated. Four main parameters like rectangular variable aperture (RVA-XY) size, number of pulse, stage/table feed rate and laser energy play important role in laser ablation process. The pattern of the microchannel or line with 1 cm length was drawn by AutoCAD software or any CAD software. The pattern in the CAD software is then transferred onto the silicon wafer by using laser micromachining. Finally, high power microscope (HPM) and Stylus Profiler will be used as measurement tools for observing and analysing the width and depth of the microchannel structures fabricated by laser micromachining. When using bigger size of RVA, it will lead to bigger microchannel width. There are a little effects or almost comparable in term of microchannel depth if varying all parameters' value. Surface roughness test also needs to be considered before choosing the best setting for the laser ablation.
Development and Modeling of Laser Micromachining Techniques
Laser micromachining has great potential as a MEMS (micro-electromechanical systems) fabrication technique because of its materials flexibility and 3D capabilities. The machining of deep polymer structures with complex, well-defined surface profiles is particularly relevant to micro-fluidics and micro-optics. This paper presents the use of projection ablation methods to fabricate structures and devices aimed at these application areas. A better understanding of the mechanisms of thermodynamics and heat transfer in MEMS is desired to improve the thermal performance of MEMS due to the importance of these physical processes. Ablation rate of the laser depends on temperature, the material properties and accumulation of heat in the work material. In consequence, to control the laser processing, thermal distribution of the sample has to be determined, which can be made by modeling of laser ablation. By using such modeling tool, proper laser parameters can be determined easier and faster. Geometry of the domain under investigation varies during the simulation, because laser pulses remove material from the sample, thermal effects, photochemical and other phenomena still exist and so the modeling of laser ablation is a specialised problem. A two dimensional finite element model is developed in this work for laser ablation of polymers. Model has been further modified for fabrication of curved sufaces utilized in MEMS applications.
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.