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A major breakthrough in UV-LIGA (Lithographie, Galvanoformung and Abformung) started with the use of epoxy-based EPON® SU-8 photoresist in the mid-1990s. Using this photoresist has enabled the fabrication of tall and high aspect ratio structures without the use of a very expensive synchrotron source needed to expose the photoresist layer in X-ray LIGA. SU-8 photoresist appeared to be well-suited for LIGA templates, but also as a permanent material. Based on UV-LIGA and SU-8, Mimotec SA has developed processes to manufacture mold inserts and metallic components for various market fields. From one to three-level parts, from Ni to other materials, from simple to complicated parts with integrated functionalities, UV-LIGA has established itself as a manufacturing technology of importance for prototyping, as well as for mass-fabrication. This paper reviews some of the developments that led to commercial success in this field.

IB-LIGA (Ion Beam Lithographie, Galvanoformung and Abformung) is a new technique for the 3D structuring of photoresist materials. It is a direct-write (maskless) technique that uses high energy (0.5-3.5 McV) light ions (protons or helium ions) for the irradiation of photoresist materials. At CAFI (Centre d'Analyse par Faisceau Ionique), the IB-LIGA technique has been implemented. The experimental parameters for irradiation and the subsequent development have been optimised for PMMA. The results obtained so far are presented. These results include irradiations with different beam energies to control the depth, different sample tilt angles to produce sloping structures, and production of walls by moving the sample. Real 3D structures can be obtained in this way as shown in the examples. These examples show that structures in PMMA can be obtained with smooth near 90degrees side walls and bottom surfaces with low roughness. High aspect ratios have also been obtained, the current maximum is about 40. An ion- beam focussing system has recently been installed at CAFI, to produce ion- beams with sub-micrometer dimensions which can be accurately scanned in an arbitrary pattern over an area of 2.5 X 2.5 mm. (C) 2003 Elsevier Science B.V. All rights reserved.

An innovative method for fabrication and rapid prototyping of high-aspect ratio micromechanical components in photoresist is discussed. The photoresist is an epoxy-negative-tone resist, called SU-8, which can be structured to more than 2 mm in thickness by UV exposure. Small gears of 530 mu m in diameter and 200 mu m in thickness have been realized in this photoplastic and their functionality has been demonstrated. In addition a process called MIMOTEC(TM) (MIcroMOlds TEChnology) has been established for the fabrication of metallic micromolds. MIMOTEC(TM) is based on the use of the SU-8 spun on high thicknesses and electrodeposition of nickel. Thermoplastic microcomponents have been injected and mounted in watches.

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.

A high-sensitivity flat-coil inductive proximity sensor microsystem has been realized and successfully tested. The flat coil, made with CMOS-compatible post processes, is connected to a versatile differential relaxation oscillator electronic interface. In this new and simple interface, the excitation, the signal extraction and amplification are assured by only one operational amplifier. Experimental results on the microsystem confirm that large output frequency variations occur when a metallic target approaches the sensor.

We report on recent advances in micro fabrication technology using micromolding and high aspect ratio structuring of photopolymer. The direct application is the realization of components for millimeter-size, ultrasonic piezoelectric motors. A new fabrication process using a thick epoxy-based material (SU-8) and the electroplating of nickel is demonstrated. Photopolymer structures have also been realized and released using a positive tone resist as sacrificial layer. The main advantages over past fabrication methods are better design flexibility, simplicity of the fabrication process, the capability to combine metallic materials (Ni) with polymeric materials ( SU-8), and the use of positive tone resist as a sacrificial layer. (C) 1998 Elsevier Science S.A. All rights reserved.

An innovative technology for the realization of key elements of a microfabricated reduction unit is presented. In view of integrating the functions of gear, pinion and axle into one element, multilevel metal electroplating in a negative dry film resist mould (Riston) is used. Easier processing, inherent planarization for multilevel 3-D structures, vertical sidewalls and high thicknesses (20–50 μm/level) are shown to be the main key features of dry films. To demonstrate the process feasibility, a gear and pinion set with upper and lower axle posts has been realized with four levels of nickel.

Characterization of the mechanical and thermal properties of the high aspect- ratio, negative, UV resist, SU-S has been carried out. This resist allows for a broad range of thicknesses to be obtained with a single spin process. Standard exposure with a UV aligner has produced outstanding aspect ratios, 15 for lines and trenches. This type of performance lends itself well to MEIMS applications, packaging, micromolds, spacers, etc. Because of the simplicity of use of the resist in addition to the large range of possible applications, the process dependent mechanical and thermal properties must be understood in order to completely exploit the potential of the resist.

We report on recent advances in micro fabrication technology using micromoulding and high-aspect ratio structuring of photopolymer. The direct application is the realization of components for millimeter-size, ultrasonic piezoelectric motors. A new fabrication process using a thick epoxy-based material (SU-8) and the electroplating of nickel is demonstrated. Photopolymer structures have also been realized and released using a positive tone resist as sacrificial layer. The main advantages over past fabrication methods are better design flexibility, simplicity of the fabrication process, the capability to combine metallic materials (Ni) with polymeric materials (SU-8), and the use of positive tone resist as a sacrificial layer.

Briefly reports on advances in the fabrication technology of components for millimeter size ultrasonic piezoelectric motors. A very large height to width aspect ratio with good lateral patterning resolution is required for the active component in acoustic mode conversion. A new fabrication process using a thick epoxy-based material (SU-8) and the electroplating of nickel is demonstrated. The main advantages over past fabrication methods are better flexibility in the design, simplicity of the fabrication process and the combination of metallic materials (Ni) with polymeric materials (SU-8). The mechanical properties of SU-8 have been measured using free cantilever beam structures.

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 /spl mu/m can be achieved reproducibly. Thicker resist layers can be made by multiple coatings, and we have achieved exposures in 1200-/spl mu/m-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 /spl mu/m. 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 resist thicknesses. These results will open up new possibilities for low-cost LIGA-type processes for MEMS applications. In addition, the SU-8 material has interesting mechanical properties which also makes it attractive for photoplastic device fabrication.

This paper describes the characterization of a home-made negative photoresist developed by IBM. This resist, called SU-8, can be produced with commercially available materials. Three blends were prepared for this article and some of its optical and mechanical properties are presented. One of its numerous advantages is the broad range of thicknesses which can be obtained in one spin: from 750 nm to 450 mu m with a conventional spin coater. The resist is exposed with a standard UV aligner and has an outstanding aspect ratio near 15 for lines and 10 for trenches. These ratios combined with the electroplating of copper allow the fabrication of highly integrated electromagnetic coils.

A new approach for the realization of true 3D polymer structures is presented in this paper. It consists in adding, in a post-processing microstereolithography step, 3D polymer microstructures on top of a micropart patterned by means of planar processes such as thin films, bulk silicon etching or high aspect ratio structuration (LIGA, RIE, thick resist). In this way, some shape limitations of the planar technologies can be overcome for new functional applications. Moreover, the direct processing of microstereolithography on predefined structures eliminates manipulations which are associated with micro-assembly of separated parts. To demonstrate this combination of microstructuration processes, an example showing a conical axle added by microstereolithography on a SU-8 piece of gearing is presented. (C) 1999 Elsevier Science S.A. All rights reserved.