© 2002 by CRC Press LLC Other less obvious competing technologies for LIGA-like applications are ion-beam milling, laser ablation methods and even ultra-precision machining (see Madou [1997, chap. 7]). The latter three are serial processes and rather slow, but if we are considering making a mold then these technologies might be competitive. References Akkaraju, S., Y. M. Desta, B. Q. Li, and M. C. Murphy, “A LIGA-Based Family of Tips for Scanning Probe Applications,” SPIE, Microlithography and Metrology in Micromachining II, Austin, TX, 1996, pp. 191–198. Anderer, B., W. Ehrfeld, and D. Munchmeyer, “Development of a 10–Channel Wavelength Division Multiplexer/Demultiplexer Fabricated by an X-Ray Micromachining Process,” SPIE, 1014, 17–24, 1988. Becker, E. W., W. Ehrfeld, D. Munchmeyer, H. Betz, A. Heuberger, S. Pongratz, W. Glashauser, H. J. Michel, and V. R. Siemens, “Production of Separation Nozzle Systems for Uranium Enrichement by a Combination of X-Ray Lithography and Galvanoplastics,” Naturwissenschaften, 69, 520–523, 1982. Becker, E. W., W. Ehrfeld, and D. Munchmeyer, “Untersuchungen zur Abbildungsgenauigkeit der Ront- gentiefenlitographie mit Synchrotonstrahlung,” KfK, Report No. 3732, Karlsruhe, Germany, 1984. Becker, E. W., W. Ehrfeld, P. Hagmann, A. Maner, and D. Munchmeyer, “Fabrication of Microstructures with High Aspect Ratios and Great Structural Heights by Synchrotron Radiation Lithography, Galvanoforming, and Plastic Molding (LIGA process),” Microelectron. Eng., 4, 35–56, 1986. Bley, P., J. Gottert, M. Harmening, M. Himmelhaus, W. Menz, J. Mohr, C. Muller, and U. Wallrabe, “The LIGA Process for the Fabrication of Micromechanical and Microoptical Components,” in Micro- system Technologies ’91, Krahn, R. and Reichl, H., Eds., VDE-Verlag, Berlin, 1991, pp. 302–314. Bley, P., W. Menz, W. Bacher, K. Feit, M. Harmening, H. Hein, J. Mohr, W. K. Schomburg, and W. Stark, “Application of the LIGA Process in Fabrication of Three-Dimensional Mechanical Microstruc- tures,” 4th International Symposium on MicroProcess Conference, Kanazawa, Japan, 1991, pp. 384– 389. Bley, P., D. Einfeld, W. Menz, and H. Schweickert, “A Dedicated Synchrotron Light Source for Micro- mechanics,” EPAC92. Third European Particle Accelerator Conference, Berlin, Germany, 1992, pp. 1690–2. Burbaum, C., J. Mohr, P. Bley, and W. Ehrfeld, “Fabrication of Capacitive Acceleration Sensors by the LIGA Technique,” Sensors and Actuators A, 25, 559–563, 1991. Bustgens, B., W. Bacher, W. Menz, and W. K. Schomburg, “Micropump Manufactured by Thermoplastic Molding,” Proceedings. IEEE Micro Electro Mechanical Systems (MEMS ’94), Oiso, Japan, January 1994, pp. 18–21. Desta, Y. M., M. Murphy, M. Madou, and J. Hines, “Integrated Optical Bench for a CO 2 Gas Sensor,” Microlithography and Metrology in Micromachining, (Proceedings of the SPIE), Austin, TX, 1995, pp. 172–177. Editorial, “Fibre Ribbon Ferrule Insert Made by LIGA,” Commercial brochure, 1994a. Editorial, “Micro-Optics at IMM,” Commercial brochure, 1994b. Editorial, “X-Ray Scanner for Deep Lithography,” Commercial brochure, 1994c. Ehrfeld, W., “The LIGA Process for Microsystems,” Proceedings. Micro System Technologies ’90, Berlin, Germany, 1990, pp. 521–528. Ehrfeld, W., “LIGA at IMM,” Notes from handouts, 1994, Banff, Canada. Ehrfeld, W., W. Glashauer, D. Munchmeyer, and W. Schelb, “Mask Making for Synchrotron Radiation Lithography,” Microelectron. Eng., 5, 463–470, 1986. Ehrfeld, W., P. Bley, F. Gotz, P. Hagmann, A. Maner, J. Mohr, H. O. Moser, D. Munchmeyer, W. Schelb, D. Schmidt, and E. W. Becker, “Fabrication of Microstructures Using the LIGA Process,” Proceed- ings of the IEEE Micro Robots and Teleoperators Workshop, Hyannis, MA, 1987, pp. 1–11. © 2002 by CRC Press LLC Other less obvious competing technologies for LIGA-like applications are ion-beam milling, laser ablation methods and even ultra-precision machining (see Madou [1997, chap. 7]). The latter three are serial processes and rather slow, but if we are considering making a mold then these technologies might be competitive. References Akkaraju, S., Y. M. Desta, B. Q. Li, and M. C. Murphy, “A LIGA-Based Family of Tips for Scanning Probe Applications,” SPIE, Microlithography and Metrology in Micromachining II, Austin, TX, 1996, pp. 191–198. Anderer, B., W. Ehrfeld, and D. Munchmeyer, “Development of a 10–Channel Wavelength Division Multiplexer/Demultiplexer Fabricated by an X-Ray Micromachining Process,” SPIE, 1014, 17–24, 1988. Becker, E. W., W. Ehrfeld, D. Munchmeyer, H. Betz, A. Heuberger, S. Pongratz, W. Glashauser, H. J. Michel, and V. R. Siemens, “Production of Separation Nozzle Systems for Uranium Enrichement by a Combination of X-Ray Lithography and Galvanoplastics,” Naturwissenschaften, 69, 520–523, 1982. Becker, E. W., W. Ehrfeld, and D. Munchmeyer, “Untersuchungen zur Abbildungsgenauigkeit der Ront- gentiefenlitographie mit Synchrotonstrahlung,” KfK, Report No. 3732, Karlsruhe, Germany, 1984. Becker, E. W., W. Ehrfeld, P. Hagmann, A. Maner, and D. Munchmeyer, “Fabrication of Microstructures with High Aspect Ratios and Great Structural Heights by Synchrotron Radiation Lithography, Galvanoforming, and Plastic Molding (LIGA process),” Microelectron. Eng., 4, 35–56, 1986. Bley, P., J. Gottert, M. Harmening, M. Himmelhaus, W. Menz, J. Mohr, C. Muller, and U. Wallrabe, “The LIGA Process for the Fabrication of Micromechanical and Microoptical Components,” in Micro- system Technologies ’91, Krahn, R. and Reichl, H., Eds., VDE-Verlag, Berlin, 1991, pp. 302–314. Bley, P., W. Menz, W. Bacher, K. Feit, M. Harmening, H. Hein, J. Mohr, W. K. Schomburg, and W. Stark, “Application of the LIGA Process in Fabrication of Three-Dimensional Mechanical Microstruc- tures,” 4th International Symposium on MicroProcess Conference, Kanazawa, Japan, 1991, pp. 384– 389. Bley, P., D. Einfeld, W. Menz, and H. Schweickert, “A Dedicated Synchrotron Light Source for Micro- mechanics,” EPAC92. Third European Particle Accelerator Conference, Berlin, Germany, 1992, pp. 1690–2. Burbaum, C., J. Mohr, P. Bley, and W. Ehrfeld, “Fabrication of Capacitive Acceleration Sensors by the LIGA Technique,” Sensors and Actuators A, 25, 559–563, 1991. Bustgens, B., W. Bacher, W. Menz, and W. K. Schomburg, “Micropump Manufactured by Thermoplastic Molding,” Proceedings. IEEE Micro Electro Mechanical Systems (MEMS ’94), Oiso, Japan, January 1994, pp. 18–21. Desta, Y. M., M. Murphy, M. Madou, and J. Hines, “Integrated Optical Bench for a CO 2 Gas Sensor,” Microlithography and Metrology in Micromachining, (Proceedings of the SPIE), Austin, TX, 1995, pp. 172–177. Editorial, “Fibre Ribbon Ferrule Insert Made by LIGA,” Commercial brochure, 1994a. Editorial, “Micro-Optics at IMM,” Commercial brochure, 1994b. Editorial, “X-Ray Scanner for Deep Lithography,” Commercial brochure, 1994c. Ehrfeld, W., “The LIGA Process for Microsystems,” Proceedings. Micro System Technologies ’90, Berlin, Germany, 1990, pp. 521–528. Ehrfeld, W., “LIGA at IMM,” Notes from handouts, 1994, Banff, Canada. Ehrfeld, W., W. Glashauer, D. Munchmeyer, and W. Schelb, “Mask Making for Synchrotron Radiation Lithography,” Microelectron. Eng., 5, 463–470, 1986. Ehrfeld, W., P. Bley, F. Gotz, P. Hagmann, A. Maner, J. Mohr, H. O. Moser, D. Munchmeyer, W. Schelb, D. Schmidt, and E. W. Becker, “Fabrication of Microstructures Using the LIGA Process,” Proceed- ings of the IEEE Micro Robots and Teleoperators Workshop, Hyannis, MA, 1987, pp. 1–11. © 2002 by CRC Press LLC 18 X-Ray-Based Fabrication 18.1 Introduction 18.2 DXRL Fundamentals X-Ray Mask Fabrication • Thick X-Ray Photoresist • DXRL Exposure (Direct LIGA Approach) • Development • PMMA Mechanical Properties 18.3 Mold Filling 18.4 Material Characterization and Modification 18.5 Planarization 18.6 Angled and Re-entrant Geometry 18.7 Multilayer DXRL Processing 18.8 Sacrificial Layers and Assembly 18.9 Applications Precision Components • Microactuators • Magnetic Microactuator Applications • Other Applications 18.10 Conclusions Acknowledgments 18.1 Introduction Originally conceived for the fabrication of smaller microelectronic features, X-ray lithography has also proven to possess attributes of great utility in micromechanical fabrication. In contrast to the many micromachining processes that have been developed from microelectronic processing, however, X-ray- based approaches may be largely carried out independent of a tightly controlled clean-room environment. The mode of X-ray-based microfabrication most commonly used places this type of processing in the additive category where a sacrificial mold is used to define the desired structural material. As a result, this technique lends itself to a very rich and ever-expanding material base including a variety of plastics, metals and glasses, as well as ceramics and composites. The idea of using X-rays to define molds extends from the 1970s, when its precedent involved the definition of high-density coils for magnetic recording read/write heads and high-density magnetic bubble memory overlays when ultimately the use of X-rays for very large-scale integration (VLSI) lithography was initially investigated [Romankiw et al., 1970; Romankiw, 1995; Spiller et. al., 1976; Spears and Smith, 1972]. The distinction from VLSI X-ray lithog- raphy is that the mold or photoresist thickness for micromachining interests is generally much greater than 50 µ m and may be well over 1 mm. X-ray processing at these thicknesses has prompted the nomenclature deep X-ray lithography or DXRL-based microfabrication. The primary utility of DXRL processing extends from its ability to precisely and accurately define a mold. Consequent component definition via mold filling is thus directly determined by mold acuity. Exceptional definition in this regard is possible with highly collimated X-rays that may be obtained via Todd Christenson Sandia National Laboratories © 2002 by CRC Press LLC 19 Electrochemical Fabrication (EFAB TM ) 19.1 Introduction 19.2 Background Solid Freeform Fabrication • SFF for Microfabrication 19.3 A New SFF Process Why Use Electrodeposition? • Selective Electrodeposition 19.4 Instant Masking A Printing Plate for Metal • Instant Masking Performance 19.5 EFAB Multiple-Material Layers • Process Steps 19.6 Detailed Process Flow Mask Making • Substrate Preparation • EFAB Layer Cycle • Post-Processing 19.7 Microfabricated Structures 19.8 Automated EFAB Process Tool 19.9 Materials for EFAB 19.10 EFAB Performance Accuracy • Materials Properties 19.11 EFAB Compared with Other SFF Processes 19.12 EFAB Compared with Other Microfabrication Processes 19.13 EFAB Limitations and Shortcomings 19.14 EFAB Applications 19.15 The Future of EFAB Acknowledgments Definitions 19.1 Introduction Electrochemical fabrication (EFAB TM ) is an emerging micromachining technology invented at the University of Southern California and licensed to MEMGen Corporation [Cohen, 1998; 1999; Tseng et al., 1999]. It is based on multilayer electrodeposition of material using a new selective deposition technique called Instant Masking TM which provides a simpler, faster and readily automated alternative to through-mask electroplating. EFAB is based on the paradigm of solid freeform fabrication (SFF), rather than the semiconductor clean-room fabrication paradigm on which conventional micromachining is based. The technology is targeted at prototyping and volume production of functional microscale components, devices and systems. Adam L. Cohen MEMGen Corporation © 2002 by CRC Press LLC 20 Fabrication and Characterization of Single-Crystal Silicon Carbide MEMS 20.1 Introduction 20.2 Photoelectrochemical Fabrication Principles of 6H-SiC 20.3 Characterization of 6H-SiC Gauge Factor Resistor–Diaphragm Modeling • Temperature Effect on Gauge Factor • Temperature Effect on Resistance 20.4 High-Temperature Metallization General Experimental and Characterization Procedure • Characterization of Ti/TiN/Pt Metallization • Ti/TaSi 2 /Pt Scheme 20.5 Sensor Characteristics 20.6 Summary Acknowledgments 20.1 Introduction For the purpose of precision instrumentation to better enable accurate measurements in high-temperature environments ( > 500 ° C), there is a growing need for sensing and electronic devices capable of operating reliably for a reasonable length of time in such a harsh environment. Typical applications for sensors that function at high temperature include automotive, aeropropulsion (both commercial and military), process control in materials engineering, and a host of others. Temperatures in these can go as high as 500 ° C or greater. However, most existing electronic components are limited to temperatures lower than 200 ° C, primarily due to the thermal limitations imposed by the conventional materials used in their manufacture (most notably silicon). Robust device architecture based on silicon-on-insulator (SOI) technology can extend device operation to near 400 ° C, either for brief period of time or with water- cooling-assisted packaging. However, at 500 ° C the thermomechanical deformation of silicon becomes the ultimate factor limiting high-temperature silicon microelectromechanical (MEMS) devices [Huff et al., 1991]. Therefore, to meet the increasing need for higher temperature instrumentation, new and inno- vative devices from materials more robust than silicon are being developed by various groups. Technological advancement in the growth of wide band-gap semiconductor crystals such as silicon carbide (SiC) has made it possible to extend the operation of solid-state devices and MEMS beyond 500 ° C. Silicon carbide has long been viewed as a potentially useful semiconductor material for high-temperature Robert S. Okojie NASA Glenn Research Center . W. Menz, and W. K. Schomburg, “Micropump Manufactured by Thermoplastic Molding,” Proceedings. IEEE Micro Electro Mechanical Systems (MEMS ’94), Oiso, Japan, January 1994, pp. 18–21. Desta, Y. M. ,. W. Menz, and W. K. Schomburg, “Micropump Manufactured by Thermoplastic Molding,” Proceedings. IEEE Micro Electro Mechanical Systems (MEMS ’94), Oiso, Japan, January 1994, pp. 18–21. Desta, Y. M. ,. developed from microelectronic processing, however, X-ray- based approaches may be largely carried out independent of a tightly controlled clean-room environment. The mode of X-ray-based microfabrication