Digital Holography is a modern coherent-optical technique that allows the direct access to the interference phase in holographic interferometry. In contrast to conventional tactical measurement techniques digital holographic interferometry provides full-field access, non-invasivity, 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. The measured interference phase contains the information about the shape of the object under test and/or its deformation after loading. These data can be used to investigate the materials' behavior of microcomponents. In combination with special loading techniques and physical models of the loading behavior of the investigated components some important material parameters such as the Young's modulus, the Poisson ratio and the thermal expansion coefficient of microcomponents can be measured. The paper describes the measuring technology and shows some examples of micro component testing.

Testing of micro-electro-mechanical systems (MEMS) for optimization purposes or reliability checks can be supported by device visualization whenever an optical access is available. The difficulty in such an investigation is the short time duration of dynamical phenomena in micro devices. This paper presents a test setup to visualize movements within MEMS in real-time and in two perpendicular directions. A three-dimensional view is achieved by the combination of a commercial high-speed camera system, which allows to take up to 8 images of the same process with a minimum interframe time of 10 ns for the first direction, with a second visualization system consisting of a highly sensitive CCD camera working with a multiple exposure LED illumination in the perpendicular direction. Well synchronized this provides 3-D information which is treated by digital image processing to correct image distortions and to perform the detection of object contours. Symmetric and asymmetric binary collisions of micro drops are chosen as test experiments, featuring coalescence and surface rupture. Another application shown here is the investigation of sprays produced by an atomizer. The second direction of view is a prerequisite for this measurement to select an intended plane of focus.

In photogrammetry several images of an object taken from different positions in space, are combined to calculate 3D geometrical data. This concept can be scaled down to dimensions in the mm or sub-mm regime. In this paper the application of microphotogrammetry for the measurement of strain fields in material testing is presented. The working principle and an experimental measurement setup are described and results of two application examples are given. Microphotogrammetry is compared with speckle-interferometry as an alternative approach for strain field measurement. As an additional implementation of the microphotogrammetric approach the current state of development of a precision assembly system with a positioning control using CCD-cameras is discussed.

White light fringe scanning interferometric profilometry is increasingly used for 3D full field measurements of the surface topography and of the static deformations of MEMS because it can be applied, contrary to most interferometric technique using monochromatic illumination, to surfaces having large discontinuities and patterns with a complex geometry. In this paper it is demonstrated that this technique is also well suited for 3D full field measurements of MEMS vibrations provided that a stroboscopic LED array source is used. A fast algorithm based on quadrature filtering of the interferometric signal is described to determine for each pixel the maximum of the fringe envelope when the sample is translated. 3D measurements of the vibration modes of micromechanical devices with a complex shape and/or an initial deformation are demonstrated up to 570 kHz. A spatial resolution in the micrometer range and a detection limit of 5 nm have been obtained.

Characterizing the mechanical properties of MEMS structures at a very early stage of manufacturing is a challenging task for quality assurance in this field. The paper describes a new solution that is based upon the vibration analysis of the microparts. The microvibrations have nm amplitudes and are detected by electronic speckle pattern interferometry (ESPI). A specific signal processing technique (moving phase reversal reference) has been applied to make the solution robust. Comprehensive numerical simulations provide the theoretical base for estimating the frequencies and mode shapes expected for perfect MEMS as well as for typical faults. The complete wafer ensemble was modeled to gain knowledge about best suited wafer clamping and about interactions between the microparts vibrating. A laboratory system for 4' wafer has been built, and extensive tests show that such key properties as e.g. the thickness of springs or membranes can be determined exactly by means of the hybride approach. Automated frequency scanning and corresponding digital image processing open the way to reliable and fast industrial systems for MEMS testing on wafer level.

Interferometric optical profilometers are increasingly used for the characterization of the static deformation of micromechanical devices and Micro(Opto)Electromechanical Systems (M(O)EMS). Recent works have shown that they can also be used for full field dynamic measurements provided that a stroboscopic light source is added or that time averaging of the interferograms is performed. In this work we investigate two methods to make quantitative time-averaged microscopic interferometric measurements. Both methods are based on the calibration of the fringe contrast variation as function of the vibration amplitude. It is demonstrated from experiments on micromechanical devices that 3D vibration modes shapes can be measured at any frequency with a spatial resolution in the micrometer range and a detection limit around 5 nm.

Photo-acoustic microscopy (laser ultrasonics) is a potentially powerful tool for nondestructive, in situ, MEMS device characterization. This paper discusses the use of narrowband photo-acoustics to characterize the properties of free-standing nanometer-sized thin films. Photo-acoustic generation is achieved by use of a micro-chip laser which deposits pulsed laser energy (10mJ in 300 picoseconds) in the form of a spatially periodic source on the structure. The resulting narrowband ultrasonic modes are monitored using a Michelson interferometer. By varying the geometry of the spatially-periodic source, a wide range of wavenumbers is probed. Experiments were conducted on two-layer Al/Si3N4 membranes (aluminum thickness: 300-500nm; silicon nitride thickness: 240-400nm. For such thin films, only the two lowest order modes are generated and these in turn can be related to sheet and flexural modes in plates. The mechanical properties and residual stress in the thin films are evaluated from the dispersion curves for these two lowest order modes.

A newly developed miniature phase-modulation variable angle Ellipsometer named PEARL was detailed. PEARL is an acronym of Paraboloidal Ellipsometer with Accurate Retardance and Latitude. This newly developed system was designed by using a diamond turned axis-symmetric paraboloidal metallic mirror and a concave spherical mirror to accurately control the incident angle of the probing light beam. The penta prism carried by a precision servomotor was designed to change the incident light beam. Coupling the 0.4mm accuracy of today's servomotor, the extreme accurate figure achieved by the diamond turning machine, and the newly invented metallic mirror set, PEARL achieved the goals of miniaturization and with accurate incident angle control. The built-in self-calibration system of PEARL, which provide us with an opportunity to eliminate the expensive and hard-to-maintain standard specimen was also discussed. Modification to the paraboloidal mirror and the spherical mirror in order to resolve the non-unique probing point problem in in-situ process control of semiconductor processing and flying height measurement of magnetic disk drives will also be detailed.

This investigation deals with various new aspects of the sensitivity improvement of a pump-probe laser based acoustic method. A short laser pulse is used to excite a mechanical pulse thermo-elastically. Echoes of these mechanical pulses reaching the surface are causing a slight change of the optical reflectivity. The surface reflectivity is scanned versus time with a probe pulse. Thus the time of flight of the acoustic pulse is measured. The quantity to be measured i.e. the optical reflectivity change DR caused by acoustic pulses, is rather small. A set-up having an estimated sensitivity DR/R of about 10(superscript -5 has shown to be sufficient to detect up to the 5th echo in a 50 nm aluminum film on sapphire substrate. A key challenge is the reduction of optical and electrical cross talk between the excitation and the detection. Therefore the concepts of double-frequency modulation, cross-polarization, and balanced-photo-detection are implemented. Practical aspects like beam guiding, modulation techniques, beam focus-minimization, beam focus-matching, and the variation of the pump-probe power ratio are discussed. Measurements for single and multi-layer metallic films demanding higher sensitivity are presented.

Optical measuring techniques in MEMS are attractive ways of detection and reproducible methods. Applications of appropriate optical measuring techniques can be found in many situations: local study of materials constants, characterization of micromechanical systems, vibration analysis, and environmental behavior.

The increased use of micromechanical devices demands the miniaturization of corresponding testing- and evaluation methods. The well known scanning probe methods (SPM) have very high lateral resolution. Pulsed laser acoustic experiments on the other hand have the advantage of very high temporal resolution, whereas the lateral resolution is limited by the fact that the minimal spot size to which a laser pulse can be optically focused amounts to several wavelengths of light. The mechanical wavelength of acoustic waves excited by a ultra short laser pulse amounts to 10 to 20 nm. In contrast the spot size of the laser pulse is three orders of magnitude larger. The presented approach to improve the lateral resolution is the combination of the conventional scanning probe methods with pulsed laser acoustic methods. The introduction of a micro-opto-mechanical focusing tip in which the mechanical waves are focused leads to a new potential time resolved scanning probe technique. An elastodynamic finite difference method has been developed to investigate the ultrasonic wave propagation in the tip numerically. The mechanical wave propagation for a conical tip geometry is discussed. The numerically calculated results are verified by experiments with structures having macroscopic dimensions. Scaling effects and restrictions due to the pulsed laser experiment are considered in order to translate the results into the microscopic scale.

We propose to fabricate GaAlAs/GaAs multi-layer microtips for scanning near-field optical microscopy (SNOM) using the anisotropic etching. The etching was performed in a solution of H₃PO₄:H₂O₂:H₂O, operating at the temperature of 10 degrees C. We obtained the pyramid-shaped microtips with four etched facets and with a radius of curvature at the apex lower than 50 nm.

Industrialization of MEMS devices such as silicon-based sensors and actuators requires specific tools to verify that their mechanical properties and/or motions obey the designer's's intent. Accordingly, this paper investigates new on-chip laboratories that will allow systematic mechanical analysis of MEMS-based structures and materials.

The maturing designs of moving microelectromechanical systems (MEMS) make it more-and-more important to have precise measurements and visual means to characterize dynamic microstructures. The Berkeley Sensor&Actuator Center (BSAC) has a forefront project aimed at developing these capabilities and at providing high-speed Internet (Supernet) access for remote use of its facilities. Already in operation are three optical-characterization tools: a stroboscopic-interferometer system, a computer-microvision system, and a laser-Doppler vibrometer. This paper describes precision and limitations of these systems and discusses their further development. In addition, we describe the results of experimental studies on the different MEMS devices, and give an overview about high-speed visualization of rapidly moving MEMS structures.

In this paper the measurement concept based on full-field optical methods is presented. In order to fulfil most of the requirements connected with advanced micro element and micro material testing a waveguide micro interferometer based on grating interferometry method is proposed and described in details. The modification of this system for 3D-displacement measurements is presented. The applicability of the micro interferometer is shown at the examples of silicon beam and micro membranes testing.

Nowadays large area microstructured surfaces can be produced by innovative production technologies. The task for the measurement technologies is to cover the process chain during the production of these 3D-nano- and microstructures. At the Fraunhofer IPT the form of the structures is investigated because it determines the functionality of the components most significantly. Fast interferometrical measurement concepts are developed for the inspection of the surface. The possibilities of interferometrical formtesting of prisms, spherical lens arrays or gratings are adapted to the microscopic range. Especially for the characterization of gratings, the measurement range has been extended by using multiple wavelength interferometry.

We have developed a new design of advanced optics for processing high-power laser material. We introduce the concept of DOE for high power CO₂ lasers. The superior functionality of DOE means that it could become the new standard in optics for next generation devices. Here we describe the design of our DOE technology using scalar theory and micro fabrication using photolithography and RIE. We also present results of our ZnSe-DOE technology, mainly focusing on a novel spot-array generator.

An experimental set-up designed for the mechanical characterization of small-size membranes by the bulge test and blister test techniques is described. The differential pressure (0-10 bars) is applied to the membrane with a motorized microsyringe pump filled with water to minimize stored elastic energy in the system. An interferometric microscope equipped with a quasi monochromatic Na discharge lamp, a CCD camera and an apertured photomultiplier is used to get simultaneously full field interferograms of the membrane deformed shape and a point measurement of the membrane central height variation. Phase extraction by FFT and unwrapping of the photomultiplier output signal, and processing of some pixels corresponding to the substrate in the set of interferograms images allows to get, with an accuracy in the 3-30 nm range, the true membrane maximum deflection corrected from substrate bending, vertical drift and tilting. 2D or 3D profiles of the membrane deformed shape can as well be obtained with a similar accuracy and a spatial resolution of 3micrometers . The good performances of the system are illustrated from measurements on micromachined Si3N4 and Mo membranes on silicon.

Results on extended studies on mechanical properties of polarimetric fiber-optic smart structures are presented. The smart structure consists of highly birefringent fiber embedded in an epoxy cylinder.