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Optical microsystems metrology
Optics and Lasers in Engineering 36 (2001) 75–76
Editorial Optical microsystems metrology High quality standards are a must for the majority of manufacturers from all over the world. This applies to a large extent to microsystems technology. Strict requirements must be fulfilled here with respect to reliability and lifetime if relevant products can be used in medicine, telecommunication and safety engineering. The development of new materials and processing technologies, combined with advanced structural design, contributes significantly to this process. However, it is well known that the materials’ behavior cannot be easily predicted by theoretical simulations. A possible reason for wrong predictions made by FEM calculations with respect to the loading behavior of microdevices is the lack of reliable materials data and boundary conditions in the microscale. Properties determined on much larger specimens cannot be scaled down from the bulk material without any experimental verification. Furthermore in microscale the materials’ behavior is noticeably affected by the production technology. Therefore, simple and robust methods to analyze basic properties like the shape and the deformation of the microcomponents are needed. Conventional tensile test techniques (e.g. strain gauges) are unable to test specimens from submillimeter-sized regions because of their limited local resolution and partly unwanted tactile character. Other approaches, such as, micro-hardness measurements, do not reveal directional variations. A promising alternative to the conventional techniques can be provided by fullfield optical methods. The main advantages of these methods are: non-invasive and fieldwise character; high sensitivity and accuracy; high resolution of data points and advanced system performance in order to meet requirements of the underlying numerical or analytical model. To provide a timely review of the research into the application of modern optical measurement techniques for the investigation of microsystems and their basic components, Optics and Lasers in Engineering published in 2000 a call for papers dedicated to this subject. The international response to this call was extremely positive. Almost 30 contributions submitted by well-known research groups from all over the world had to be evaluated. As the result of a careful reviewing process, 19 papers were finally selected for the special issue. This first volume contains 10 papers dealing with the application of different optical measurement techniques such as interferometry, holography, structured light, image correlation and Raman spectroscopy for the inspection of microcomponents. Petitgrand et al. from the University Paris demonstrate the capability of microscopic interferometry as a powerful technique for the visualization of the vibration modes of microbeams by using stroboscopic illumination. The contribution of the Bremen Institute of Applied Beam Technology shows the advantages of 0143-8166/01/$ - see front matter r 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 3 - 8 1 6 6 ( 0 1 ) 0 0 0 5 1 - 3
76
Editorial / Optics and Lasers in Engineering 36 (2001) 75–76
digital holography for the precise whole field measurement of the shape and the displacements of microcomponents. These data are used afterwards for the determination of material parameters (Poisson’s ratio, Young’s modulus, thermal expansion coefficient). Miller et al. from Intel Corporation provide a competent insight into the analysis of an advanced flip-chip package with fine interconnection features using phase-shifting moir!e interferometry. The group from the Technical University Stuttgart compares two optical measurement techniques, white light interferometry and fringe projection, with respect to their suitability for microsystems inspection. A new approach, the so-called scanning fringe projection, enables an absolute 3D-measurement with one single grating period. Bitte et al. from the Fraunhofer Institute of Production Technology in Aachen show the application of a Digital Micromirror Device (DMD) as an array of pinholes that may substitute the Nipkow-disk used in confocal microscopes for the lateral scanning of microstructures. The application of scanning white light interferometry to profile single layer and multilayer, surface micromachined, micromechanical elements is described by Hill et al. from the National Microelectronics Research Centre in Cork, Ireland. The continuous progress in CMOS submicron technology for the production of novel imaging devices with added functionalities is considered in the article of Willemin et al. from the Centre Suisse d’Electronique et de Microtechnique in Zu. rich. Modern measurement techniques for a reliable inspection of the most relevant parameters of imaging sensors are described. Vogel et al. from the Fraunhofer Institute for Reliability and Microintegration in Berlin utilize correlation techniques to measure the deformations of solder interconnects of flip chip and chip scale packages. Emphasis is made with respect to the support of Finite Element Simulation by means of experimental validation of mechanical modeling. The contribution from the IMEC Leuven in Belgium discusses the use of Raman spectroscopy to study the functioning and reliability of microsystems. This interesting contribution shows that Raman spectroscopy has several potential applications for the identification of materials, the study of their crystallinity, uniformity and composition and for the measurement of local temperature and stress in MEMS. Finally, a paper from the Warzaw University of Technology presents a concept of an optical measurement station for the complex testing of microelements using grating interferometry, ESPI, digital holography and thermovision. Thanks are due to all authors for their contributions that give a comprehensive impression about the state of the art in optical microsystems metrology and to all reviewers, who spent a significant amount of time in helping all authors to increase the quality of their presentations. Finally, the editor is grateful for the cooperation shown by Elsevier represented by Martin Ruck, the publishing editor in material science and engineering. W. Osten Bremer Institut fu´r Angewandte Strahltechnik (BIAS), Klagenfurter Strasse 2, D-28359 Bremen, Germany E-mail address: [email protected] May 2001
Editorial Optical microsystems metrology High quality standards are a must for the majority of manufacturers from all over the world. This applies to a large extent to microsystems technology. Strict requirements must be fulfilled here with respect to reliability and lifetime if relevant products can be used in medicine, telecommunication and safety engineering. The development of new materials and processing technologies, combined with advanced structural design, contributes significantly to this process. However, it is well known that the materials’ behavior cannot be easily predicted by theoretical simulations. A possible reason for wrong predictions made by FEM calculations with respect to the loading behavior of microdevices is the lack of reliable materials data and boundary conditions in the microscale. Properties determined on much larger specimens cannot be scaled down from the bulk material without any experimental verification. Furthermore in microscale the materials’ behavior is noticeably affected by the production technology. Therefore, simple and robust methods to analyze basic properties like the shape and the deformation of the microcomponents are needed. Conventional tensile test techniques (e.g. strain gauges) are unable to test specimens from submillimeter-sized regions because of their limited local resolution and partly unwanted tactile character. Other approaches, such as, micro-hardness measurements, do not reveal directional variations. A promising alternative to the conventional techniques can be provided by fullfield optical methods. The main advantages of these methods are: non-invasive and fieldwise character; high sensitivity and accuracy; high resolution of data points and advanced system performance in order to meet requirements of the underlying numerical or analytical model. To provide a timely review of the research into the application of modern optical measurement techniques for the investigation of microsystems and their basic components, Optics and Lasers in Engineering published in 2000 a call for papers dedicated to this subject. The international response to this call was extremely positive. Almost 30 contributions submitted by well-known research groups from all over the world had to be evaluated. As the result of a careful reviewing process, 19 papers were finally selected for the special issue. This first volume contains 10 papers dealing with the application of different optical measurement techniques such as interferometry, holography, structured light, image correlation and Raman spectroscopy for the inspection of microcomponents. Petitgrand et al. from the University Paris demonstrate the capability of microscopic interferometry as a powerful technique for the visualization of the vibration modes of microbeams by using stroboscopic illumination. The contribution of the Bremen Institute of Applied Beam Technology shows the advantages of 0143-8166/01/$ - see front matter r 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 3 - 8 1 6 6 ( 0 1 ) 0 0 0 5 1 - 3
76
Editorial / Optics and Lasers in Engineering 36 (2001) 75–76
digital holography for the precise whole field measurement of the shape and the displacements of microcomponents. These data are used afterwards for the determination of material parameters (Poisson’s ratio, Young’s modulus, thermal expansion coefficient). Miller et al. from Intel Corporation provide a competent insight into the analysis of an advanced flip-chip package with fine interconnection features using phase-shifting moir!e interferometry. The group from the Technical University Stuttgart compares two optical measurement techniques, white light interferometry and fringe projection, with respect to their suitability for microsystems inspection. A new approach, the so-called scanning fringe projection, enables an absolute 3D-measurement with one single grating period. Bitte et al. from the Fraunhofer Institute of Production Technology in Aachen show the application of a Digital Micromirror Device (DMD) as an array of pinholes that may substitute the Nipkow-disk used in confocal microscopes for the lateral scanning of microstructures. The application of scanning white light interferometry to profile single layer and multilayer, surface micromachined, micromechanical elements is described by Hill et al. from the National Microelectronics Research Centre in Cork, Ireland. The continuous progress in CMOS submicron technology for the production of novel imaging devices with added functionalities is considered in the article of Willemin et al. from the Centre Suisse d’Electronique et de Microtechnique in Zu. rich. Modern measurement techniques for a reliable inspection of the most relevant parameters of imaging sensors are described. Vogel et al. from the Fraunhofer Institute for Reliability and Microintegration in Berlin utilize correlation techniques to measure the deformations of solder interconnects of flip chip and chip scale packages. Emphasis is made with respect to the support of Finite Element Simulation by means of experimental validation of mechanical modeling. The contribution from the IMEC Leuven in Belgium discusses the use of Raman spectroscopy to study the functioning and reliability of microsystems. This interesting contribution shows that Raman spectroscopy has several potential applications for the identification of materials, the study of their crystallinity, uniformity and composition and for the measurement of local temperature and stress in MEMS. Finally, a paper from the Warzaw University of Technology presents a concept of an optical measurement station for the complex testing of microelements using grating interferometry, ESPI, digital holography and thermovision. Thanks are due to all authors for their contributions that give a comprehensive impression about the state of the art in optical microsystems metrology and to all reviewers, who spent a significant amount of time in helping all authors to increase the quality of their presentations. Finally, the editor is grateful for the cooperation shown by Elsevier represented by Martin Ruck, the publishing editor in material science and engineering. W. Osten Bremer Institut fu´r Angewandte Strahltechnik (BIAS), Klagenfurter Strasse 2, D-28359 Bremen, Germany E-mail address: [email protected] May 2001