Electrochemical post-processing of LIGA structures

 The Louisiana State University (LSU) Microsystems Engineering Team (μSET) is developing techniques for producing microstructures with predictable 3-D geometry. One approach is based on controlled anodic dissolution of electroplated structures to obtain desired shapes. A finite element model was developed to predict the resulting shapes. As a demonstration of the shaping process, development of LIGA-based scanning probe microscope tips was investigated. An array of micro-posts 1.8 micrometers in diameter and 12 micrometers high was produced using x-ray lithography and subsequent electrodeposition. The posts were sharpened electrochemically. Other geometries are being investigated. Received: 30 October 1995/Accepted: 18 December 1995     

Replication of LIGA structures using microcasting

Microcasting with a gold base alloy and an Al-bronze as a replication technique for LIGA structures is shown. A LIGA mold insert for injection molding is used to produce PMMA patterns as lost wax models in the microcasting process. Although there are several steps of replication the accuracy of the process is high and allows the fast manufacturing of middle size batches of microstructured parts. The mechanical properties can be varied within a wide range by choosing different casting alloys or cooling rates. Additionally the influence of the investment on the surface roughness is presented as well as results of flowlength tests showing maximal achievable aspect ratios with the gold base alloy and the Al-bronze.The funding of this work within Collaborative Research Center SFB 499 by Deutsche Forschungsgemeinschaft (DFG) is gratefully acknowledged. Thanks also to the colleagues in the SFB 499 for good collaboration, especially to S. Rath for providing special investments for microcasting.     

Materials of LIGA technology

 The progress in microfabrication technologies is currently characterized by an increasing number of microproducts and corresponding efforts for cost effective mass fabrication. In this context, the development and utilization of new application specific materials has become one of the key challenges for the commercial production of miniaturized functional units. This applies, in particular, to the LIGA technique, a sequence of process steps combining deep lithography, microelectroforming and micromoulding, which offers an extremely broad spectrum of materials for the generation of ultraprecise three-dimensional microstructures. A wide variety of polymers, metals, metal alloys and ceramic materials are by now accessible for fabricating microdevices. There are practically no major limitations in selecting the desired material properties, e.g. in respect of mechanical stiffness or biocompatibility, optical transparency or magnetic properties, resistance against corrosion or whatever is required by the specific function of a microdevice.     

Fabrication of LIGA mold inserts

 The present paper describes the fabrication sequence of a LIGA mold insert by electroforming after the patterning steps of the overall process. These tools are applied for large scale fabrication of microcomponents made by molding and embossing processes. The application of an intermediate layer system leads to optimized process performance and to a better surface quality of the mold insert. The plating processes are described and the materials properties, e.g. hardness, are used for the characterization of the recrystallization behavior of the electroformed nickel which yields the high temperature application limit of the tool. Received: 25 August 1997 /Accepted: 22 September 1997     

LIGA activity in Taiwan

 This paper describes activities and development of the LIGA technology in Taiwan. The third-generation synchrotron at SRRC, providing the radiation covering an energy range from VUV to soft X-ray, is fully optimized for the wide-range applications in science and technology. In its five-year plan started from 1995, SRRC has identified deep X-ray lithography and related LIGA technology as one of the main focuses of the applied research programs. To integrate a multiple discipline research, SRRC also seeks collaboration with the following organizations in Taiwan: Industrial Technology Research Institute, National Nano Device Laboratory, Chung-Shan Institute of Science and Technology, Universities and Textile Industry. In the near future, LIGA technology will be used to fabricate the microstructures for the scientific and industrial applications, such as zone plate, nozzle, sensor and heat transfer layer for VLSI. Received: 30 October 1995/Accepted: 25 January 1996     

LIGA technology in BSRF

Beijing Synchrotron Radiation Facility is a partly dedicated Synchrotron Radiation Source which is operated since the end of 1990. Some main specifications of the source are briefly illustrated. Beam line 3B1 is a soft X-ray beam line extracted from bending magnet exploited for lithography. In the end of 3B1 there is a simple exposure chamber, LIGA patterns were exposured in the chamber. The LIGA technologies in BSRF are in the basic research stage, only a few of demonstrated patterns of deep etching structure were obtained. A sample of electroplating apparatus has been set up for getting metal structure. Further plan of the next phase of LIGA technology are presented. A new exposure scanner is being designed and would be set up on the another beam line 4W1 which is extracted from wiggle source with critical wavelength 2.2 A which seems quite suitable for deep etching exposure.     

LIGA activity in Taiwan

This paper describes activities and development of the LIGA technology in Taiwan. The third-generation synchrotron at SRRC, providing the radiation covering an energy range from VUV to soft X-ray, is fully optimized for the wide-range applications in science and technology. In its five-year plan started from 1995, SRRC has identified deep X-ray lithography and related LIGA technology as one of the main focuses of the applied research programs. To integrate a multiple discipline research, SRRC also seeks collaboration with the following organizations in Taiwan: Industrial Technology Research Institute, National Nano Device Laboratory, Chung-Shan Institute of Science and Technology, Universities and Textile Industry. In the near future, LIGA technology will be used to fabricate the microstructures for the scientific and industrial applications, such as zone plate, nozzle, sensor and heat transfer layer for VLSI. During the past year, I had many valuable discussions with professor W. Menz, Dr. H. Lehr and Dr. J. Mohr who inspired and assisted in shaping the present LIGA program. I would like to thank all of our German friends. I would like to extend special thanks to professor A. C.-M. Yang at Tsing-Hua university for the preparation of the thick film photo resist. He developed a brand new method to produce the thick resist without polymerization process. My appreciation also extends to professor C.-L. Kuo at Yunlin institute of technology for the preparation of the Ta stencil mask by EDM machining. For the multiple exposure-development process, I want to thank Dr. M.-C. Jiang, the only full time staff in the LIGA program at present. In writing this paper, I have received a lot of support from the SRRC staff for providing me with the most current data and drawings of TLS. For that, I thank Dr. Ch. Wang, Dr. C.-C. Kuo, Dr. K.-K. Lin, Mr. Z.-I. Cheng and Mr. Z.-C. Chen.     

LIGA technology in BSRF

 Beijing Synchrotron Radiation Facility is a partly dedicated Synchrotron Radiation Source which is operated since the end of 1990. Some main specifications of the source are briefly illustrated. Beam line 3B1 is a soft X-ray beam line extracted from bending magnet exploited for lithography. In the end of 3B1 there is a simple exposure chamber, LIGA patterns were exposured in the chamber. The LIGA technologies in BSRF are in the basic research stage, only a few of demonstrated patterns of deep etching structure were obtained. A sample of electroplating apparatus has been set up for getting metal structure. Further plan of the next phase of LIGA technology are presented. A new exposure scanner is being designed and would be set up on the another beam line 4W1 which is extracted from wiggle source with critical wavelength 2.2 A which seems quite suitable for deep etching exposure. Received: 30 October 1995 / Accepted: 26 January 1996     

Microcomposite electroforming for LIGA technology

 Effective methods to improve hardness and thickness uniformity in electroforming for the LIGA process to produce metallic microstructures are described. The result shows the internal stress of Ni-Co alloy deposit can be well tuned between 2 to −2 kg/mm² by adding a stress release agent into the electroplating bath. A secondary cathode is applied to improve the thickness uniformity in electroforming without loss plating rate at the center of the features. Received: 7 July 1999/Accepted: 25 November 1999     

LIGA fabrication of X-ray Nickel lenses

Nickel refractive planar lenses generating line and point X-ray spots were fabricated by LIGA technology. The optimum parameters of the lenses were simulated for a kinoform lens profile and an X-ray energy range from 100 keV to 1 MeV. The focusing elements of the lens are characterised by an aspect ratio of about 200 and a side-wall roughness of less than 5 nm r.m.s. The optical characteristics of the lenses were tested at the ESRF using a photon energy of 212 keV. A focal spot of 10 m size was measured using a X-ray sensitive film as a width at a half maximum of the darkening of this detector. A ratio of appr. 7 of the detector responses of the focused spot to the unfocused radiation was measured. The correspondent characteristics of the focal spot of the lens for the revealed photon flux are FWHM = 6 m and ~20 for the gain.     

Processing-microstructure-resulting materials properties of LIGA Ni

Electroplated nickel is the main material used in LIGA technique for fabricating MicroElectroMechanical System (MEMS) components. This paper presents the recent results regarding LIGA Ni material property enhancement at Center for Advanced Microstructures and Devices at Louisiana State University. The methodology of this study is based on the fundamental materials science paradigm that processing and manufacturing determine the microstructure of materials, which results in specific properties, and governs the performance of the structures that are made from these materials. This paper will focus on results in three aspects of our current research efforts, which are: (1) manipulating the plating parameters to tailor deposited Ni microstructures for different grain size distributions that are in the range of tens nanometer in diameters; (2) analyzing the mechanical properties, such as nano-hardness, micro-hardness, and wearing property as the function of LIGA Ni metallurgical microstructures; (3) estimating the corrosion properties of nanocrystalline LIGA Ni.     

LIGA相关技术及应用

微电子机械系统(MEMS)技术的兴起及其在现代信息社会中的广泛应用,推动了能实现高深宽比三维微细加工的LIGA及准LIGA技术的迅速发展。介绍了LIGA相关技术的发展状况并举例说明了它们在射频、光学等方面上的一些应用。     

Injection molding of polymeric LIGA HARMs

The primary goal of an ongoing research effort at LSU is to develop the three-step LIGA process to inexpensively manufacture high aspect ratio microstructures (HARMs). The first two steps of the process (lithography and electroplating) produce a metallic mold insert that can be used as a template for molding microstructures. The final step of LIGA is molding. This paper focuses on injection molding of thermoplastics to produce surfaces covered with HARMs. The resulting microstructures are hundreds of micrometers in height, tens of micrometers in width, and separated by gaps on the order of tens of micrometers. Injection molding experiments using high density polyethylene were performed using a commercially available injection molding machine. Experimental variables included injection speed, the tool temperature, and air pressure in the mold cavity. Elevating the tool temperature above the melting point ensured that the polymer completely filled the mold, producing microstructures with the desired geometry. As the temperature of the mold was reduced, higher injection speeds did not necessarily ensure filling of the mold cavity. The cycle time is shorter than the values previously reported in the literature [Madou (1996)]. Received: 30 March 1999 / Accepted: 12 April 1999     

Molding of LIGA microstructures from fluorinated polymers

 For further applications microsystem technology needs a wider range of materials and processes suited to manufacture microstructures of high chemical resistance, medical compatibility and low friction. Therefore, the fundamentals of stepped-microstructure fabrication from fluorinated polymers were developed at Forschungszentrum Karlsruhe in cooperation with the Bürkert GmbH & Co. company. It was the aim to enhance the applicabilities of the LIGA technique. First, the process for the fabrication of LIGA molding tools with two or more levels, and second, the process of vacuum hot embossing of PVDF microstructures were developed. The potentials of both developments are demonstrated by the example of molded stepped micro valve plates of PVDF. These micro valve plates were implemented in miniaturized values and tested successfully. Received: 30 October 1995 / Accepted: 12 January 1996     

Characterization of gear pumps fabricated by LIGA

 This paper presents the characterization of a positive displacement, magnetically-coupled, self-priming gear pump and a direct drive metal gear pump. In the magnetically coupled design (the in-line pump), the gears are indirectly driven by a electric motor coupled to a pair of magnets. The pump provides a flow rate of 350 μl/min at 5000 rpm, over 140 cm-H₂O (∼2 psi) of head pressure and 28.8 cm-H₂O vacuum on the suction side for a single stage pump. A two stage in-line pump generated 53 cm-H₂O vacuum at its inelt (21″H₂O). Very recently, we demonstrated a direct driven gear pump using a 3 mm smoovy^TM brushless DC motor. The direct driven pump provides a maximum flow rate of 2.5ml/min at 1200 Hz (72 krpm) and 3.6 psi dead head pressure. The direct drive pump provided 18 cm-H₂O vacuum at its inlet due to the large clearances in the first generation device. Received: 25 August 1997 / Accepted: 15 September 1997     

Molding of LIGA microstructures from fluorinated polymers

For further applications microsystem technology needs a wider range of materials and processes suited to manufacture microstructures of high chemical resistance, medical compatibility and low friction. Therefore, the fundamentals of stepped-microstructure fabrication from fluorinated polymers were developed at Forschungszentrum Karlsruhe in cooperation with the Bürkert GmbH & Co. company. It was the aim to enhance the applicabilities of the LIGA technique. First, the process for the fabrication of LIGA molding tools with two or more levels, and second the process of vacuum hot embossing of PVDF microstructures were developed. The potentials of both developments are demonstrated by the example of molded stepped micro valve plates of PVDF. These micro valve plates were implemented in miniaturized values and tested successfully.     

Photoresist application for the LIGA process

 Fabrication of high aspect ratio structures requires the use of a photoresist able to form a mold with vertical sidewalls. Thus the photoresist should have a high selectivity between the exposed and the unexposed area in the developer. It should be relatively free from stress when applied in thick layers necessary to make high aspect ratio structures. PMMA (Poly Methyl Methacrylate) is the photoresist of choice in the LIGA process, mainly for its ability to hold vertical sidewalls for tall structures. It is applied to the substrate by a glue-down process in which a pre-cast, high molecular weight, sheet of PMMA is attached to the plating base on a substrate. The applied photoresist is then milled down to the precise height by a fly-cutter prior to pattern transfer by x-ray exposure. The requirement that the applied layer be relatively free from stress dictates the choice of glue-down over casting. The substrate preparation steps, as well as the conditioning of the PMMA sheet prior to the glue-down, are done, in part, to reduce the stress in the glued down sheet of photoresist. The cutting of the PMMA sheet in the fly-cutter requires specific operating conditions as well as particular cutting tools to avoid introducing any stress and the resultant crazing of the photoresist. Received: 25 August 1997/Accepted: 3 September 1997     

New LIGA exposure source in China

 An advanced light source has been proposed by Municipality of Shanghai and the Chinese Academy of Sciences. It would be scheduled in the beginning of next century. The main propose is for the fundamental scientific research and industrial application etc. The parameters of Shanghai Synchrotron Radiation Facility (SSRF) are listed. The LIGA experimental station are planned to build in the first phase of construction of SSRF. Main parameters, spectrum and power density of beam lines for deep etching lithography are illustrated. Received: 25 August 1997/Accepted: 3 September 1997     

Silicon IC compatible LIGA mask-fabrication process

 This paper describes a technique for fabricating a LIGA mask that offers good compatibility with the silicon IC process. X-ray exposure can be eliminated from the LIGA mask-fabrication process, so that LIGA masks can be fabricated with existing silicon IC process equipment. A gold absorber pattern, 2 μm wide and 10 μm thick, has been successfully fabricated by combining a three-layer resist-patterning process with the electroplating process. Improvements in both the mask structure and fabrication process alleviate the problems of dust in a cleanroom and contamination in the etching chamber. Received: 25 August 1997/Accepted: 23 September 1997