A new fabrication process for ultra-thick microfluidic microstructures utilizing SU-8 photoresist
01 Sep 2002-Journal of Micromechanics and Microengineering (IOP Publishing)-Vol. 12, Iss: 5, pp 590-597
TL;DR: In this paper, the SU-8 50 negative photoresist (PR) was used for fabricating ultra-thick microfluidic devices using standard UV lithography.
Abstract: In this paper we describe a new process for fabricating ultra-thick microfluidic devices utilizing SU-8 50 negative photoresist (PR) by standard UV lithography. Instead of using a conventional spin coater, a simple 'constant-volume-injection' method is used to create a thick SU-8 PR film up to 1.5 mm with a single coating. The SU-8 PR is self-planarized during the modified soft-baking process and forms a highly-uniform surface without any edge bead effect, which commonly occurs while using a spin coater. Photomasks can be in close contact with the PR and a better lithographic image can be generated. Experimental data show that the average thickness is 494.32 ± 17.13 μm for a 500 μm thick film (n = 7) and the uniformity is less than 3.1% over a 10 × 10 cm2 area. In this study, the temperatures for the soft-baking process and post-exposure baking are 120 °C and 60 °C, respectively. These proved to be capable of reducing the processing time and of obtaining a better pattern definition of the SU-8 structures. We also report on an innovative photomask design for fabricating ultra-deep trenches, which prevents the structures from cracking and distorting during developing and hard-baking processes. In this paper, two microfluidic structures have been demonstrated using the developed novel methods, including a micronozzle for thruster applications and a microfluidic device with micropost arrays for bioanalytical applications.
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TL;DR: This review will introduce the currently relevant microfabrication technologies such as replication methods like hot embossing, injection molding, microthermoforming and casting as well as photodefining methods like lithography and laser ablation for microfluidic systems and discuss academic and industrial considerations for their use.
Abstract: Polymers have assumed the leading role as substrate materials for microfluidic devices in recent years. They offer a broad range of material parameters as well as material and surface chemical properties which enable microscopic design features that cannot be realised by any other class of materials. A similar range of fabrication technologies exist to generate microfluidic devices from these materials. This review will introduce the currently relevant microfabrication technologies such as replication methods like hot embossing, injection molding, microthermoforming and casting as well as photodefining methods like lithography and laser ablation for microfluidic systems and discuss academic and industrial considerations for their use. A section on back-end processing completes the overview.
840 citations
TL;DR: The SU-8 photoresist has become the favourite photoreist for high-aspect-ratio (HAR) and three-dimensional (3D) lithographic patterning due to its excellent coating, planarization and processing properties as well as its mechanical and chemical stability as mentioned in this paper.
Abstract: SU-8 has become the favourite photoresist for high-aspect-ratio (HAR) and three-dimensional (3D) lithographic patterning due to its excellent coating, planarization and processing properties as well as its mechanical and chemical stability. However, as feature sizes get smaller and pattern complexity increases, particular difficulties and a number of material-related issues arise and need to be carefully considered. This review presents a detailed description of these effects and describes reported strategies and achieved SU-8 HAR and 3D structures up to August 2006.
813 citations
TL;DR: The use of various materials, such as silicon, glass and polymers, and their related technologies for the manufacturing of simple microchannels and complex systems is discussed in this paper.
Abstract: Microfluidics is an emerging field that has given rise to a large number of scientific and technological developments over the last few years. This review reports on the use of various materials, such as silicon, glass and polymers, and their related technologies for the manufacturing of simple microchannels and complex systems. It also presents the main application fields concerned with the different technologies and the most significant results reported by academic and industrial teams. Finally, it demonstrates the advantage of developing approaches for associating polymer technologies for manufacturing of fluidic elements with integration of active or sensitive elements, particularly silicon devices.
579 citations
TL;DR: This research presents a meta-lithography program that automates and automates the very labor-intensive and therefore time-heavy and expensive and expensive process of writing and material deposition for two-Photon Lithography.
Abstract: 3.2. Two-Photon Lithography (TPL) 919 4. Serial Writing with Charged Particles 920 4.1. Electron Beam Lithography 920 4.2. Ion Beam Lithography 920 4.3. Scanning Probe Resist Lithography 921 5. Microand Nanomachining 921 5.1. Focused Ion Beam 921 5.2. Scanning Probe Nanomachining 921 6. Direct Writing and Material Deposition 921 7. Moulding 922 7.1. Mould Fabrication 922 7.2. Demoulding: Mould Treatment 924 7.3. Embossing Thermoplastic Materials: Nanoimprint Lithography (NIL) 924
445 citations
TL;DR: This work intends to discuss the potential and application examples of such processes with a detailed view on applicable materials, and point out the advantages and the disadvantages of the respective technique.
Abstract: Microfluidics is an evolving scientific field with immense commercial potential: analytical applications, such as biochemical assay development, biochemical analysis and biosensors as well as chemical synthesis applications essentially require microfluidics for sample handling, treatment or readout. A number of techniques are available to create microfluidic structures today. On industrial scale replication techniques such as injection molding are the gold standard whereas academic research mostly focuses on replication by casting of soft elastomers such as polydimethylsiloxane (PDMS). Both of these techniques require the creation of a replication master thus creating the microfluidic structure only in the second process step—they can therefore be termed two-(or multi-)step manufacturing techniques. However, very often the number of pieces to be created of one specific microfluidic design is low, sometimes even as low as one. This raises the question if two-step manufacturing is an appropriate choice, particularly if short concept-to-chip times are required. In this case one-step manufacturing techniques that allow the direct creation of microfluidic structures from digital three-dimensional models are preferable. For these processes the number of parts per design is low (sometimes as low as one), but quick adaptation is possible by simply changing digital data. Suitable techniques include, among others, maskless or mask based stereolithography, fused deposition molding and 3D printing. This work intends to discuss the potential and application examples of such processes with a detailed view on applicable materials. It will also point out the advantages and the disadvantages of the respective technique. Furthermore this paper also includes a discussion about non-conventional manufacturing equipment and community projects that can be used in the production of microfluidic devices.
318 citations
References
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TL;DR: The IBM SU-8 resist as discussed by the authors is an epoxy-based resist designed specifically for ultrathick, high-aspect-ratio MEMS-type applications and it has been shown that with single-layer coatings, thicknesses of more than 500 μm can be achieved reproducibly.
Abstract: Detailed investigations of the limits of a new negative-tone near-UV resist (IBM SU-8) have been performed. SU-8 is an epoxy-based resist designed specifically for ultrathick, high-aspect-ratio MEMS-type applications. We have demonstrated that with single-layer coatings, thicknesses of more than 500 μm can be achieved reproducibly. Thicker resist layers can be made by applying multiple coatings, and we have achieved exposures in 1200 μm thick, double-coated SU-8 resist layers. We have found that the aspect ratio for near-UV (400 nm) exposed and developed structures can be greater than 18 and remains constant in the thickness range between 80 and 1200 μm. Vertical sidewall profiles result in good dimensional control over the entire resist thickness. To our knowledge, this is the highest aspect ratio reported for near-UV exposures and the given range of resist thicknesses. These results will open up new possibilities for low-cost LIGA-type processes for MEMS applications. The application potential of SU-8 is demonstrated by several examples of devices and structures fabricated by electroplating and photoplastic techniques. The latter is especially interesting as SU-8 has attractive mechanical properties.
613 citations
"A new fabrication process for ultra..." refers background in this paper
...Lorenz et al [12] have reported that a microstructure with a height of 1.2 mm could be formed by double coating the SU-8 PR layers [12]....
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...Detailed information regarding the quantity measurement of the stress induced by the polymerization of SU-8 has been reported in the literature [12]....
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...Lorenz et al [12] have reported that a microstructure with a height of 1....
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...2 mm could be formed by double coating the SU-8 PR layers [12]....
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...Not only does internal stress distort the patterned structures but it also causes some adhesion problems or even cracking failures [12, 16, 19]....
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TL;DR: In this paper, a negative tone photoresist, SU•8, was proposed for ultrathick layer applications, achieving an aspect ratio of 10:1 using near-ultraviolet lithography in a 200μm-thick layer.
Abstract: This article describes a new negative‐tone photoresist, SU‐8, for ultrathick layer applications. An aspect ratio of 10:1 has been achieved using near‐ultraviolet lithography in a 200‐μm‐thick layer. The use of this resist for building tall micromechanical structures by deep silicon reactive‐ion etching and electroplating is demonstrated. Using SU‐8 stencils, etched depths of ≳200 μm in Si and electroplated 130‐μm‐thick Au structures with near‐vertical sidewalls have been achieved.
445 citations
IBM1
TL;DR: The history and chemistry of negative-resist systems and their development in IBM are provided and materials with wide processing latitude and high resolution are provided that are used to manufacture IBM's advanced CMOS devices and to achieve high-aspect-ratio patterns for micromachining applications.
Abstract: Negative photoresists are materials that become insoluble in developing solutions when exposed to optical radiation. They were the first systems used to pattern semiconductor devices, and still comprise the largest segment of the photoresist industry because they are widely used to define the circuitry in printed wiring boards. However, the current use of negative resists in the semiconductor industry has been limited by past difficulties in achieving high-resolution patterns. Recent advances in the chemistry of negative-resist systems, however, have provided materials with wide processing latitude and high resolution that are used to manufacture IBM's advanced CMOS devices and to achieve high-aspect-ratio patterns for micromachining applications. This paper provides an overview of the history and chemistry of negative-resist systems and their development in IBM.
427 citations
TL;DR: In this paper, a method for fabricating microfluidic devices in a photodefinable epoxy (SU-8) is described, which is compatible with and complementary to conventional fabrication techniques.
Abstract: This paper describes a method for fabricating microfluidic devices in a photodefinable epoxy (SU-8). This technique is compatible with, and complementary to, conventional fabrication techniques. It allows microstructures formed in SU-8 to be bonded to produce sealed microfluidic channels. A micromixer fabricated entirely in SU-8, using this technique, for performing liquid-phase reactions is shown to be suitable for visible spectroscopy. This fabrication method also allows the incorporation of materials that are often difficult to integrate. By fabricating hybrid devices that incorporate quartz windows, we demonstrate that these devices are compatible with organic solvents and that in situ ultraviolet detection in a microfluidic system is possible.
246 citations
"A new fabrication process for ultra..." refers background in this paper
...These fine features have been found in previous works3 [5, 10, 11] and are thought to be related to the mask problems....
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TL;DR: In this paper, the optimization results of SU-8 under UV lithography are reported and the parameters which could have an influence on the lithography quality are chosen and optimized by a three-level, L9 orthogonal array of the Taguchi method.
Abstract: In this paper, SU-8 EPON-based photoresist (PR) polymerization optimization and its possible microfluidic and MEMS applications are reported. First, the optimization results of SU-8 under UV lithography are reported. The parameters which could have an influence on the lithography quality were chosen and optimized by a three-level, L9 orthogonal array of the Taguchi method. By optimization, the optimal parameter range and the weighted per cent of a parameter on the final results were determined. For SU-8-5 and SU-8-50, many microstructures with thicknesses of more than 100 and 500 µm and aspect ratios of more than 20 and 50 were obtained with high resolution. The optimization results show that the prebake time plays the key role in the quality, which is different from the previously published results. With the optimization results obtained, some possible applications of SU-8 were developed and demonstrated. These applications included using SU-8 as a structural material for a microfluidic system, as a micromold for electroplating, as a master for plastic hot-embossing, and even as a mask for some wet-etching processes.
241 citations