No abstract

, "In situ bow change of Al-alloy MEMS micromirrors during 248-nm laser irradiation," J. Micro/Nanolith. MEMS MOEMS 15(3), 035502 (2016),

The Fraunhofer Institute for Photonic Microsystems (Fraunhofer IPMS) develops spatial light modulators (SLMs) based on arrays of tiltable micro mirrors on a semiconductor chip. Typical applications are pattern generation for deep UV-laser mask writing or structured illumination in microscopy. Development and optimization of such SLMs requires detailed knowledge of the device behaviour under operating conditions. Here, the flatness of each single mirror effects the image resolution and contrast of the generated pattern and is amongst others a characteristic property of SLMs. In this context a surface topography measurement under laser exposure (in situ) was designed. The interferometric setup uses the phase-shift principle and allows a resolution in z-direction in the single-digit nanometer range. During irradiation with UV-laser light at 248 nm (KrF) and energy densities of up to 20 mJ/cm 2 the change in single micro-mirrors topography was detected in situ. Measurements with varying pulse energies were carried out to identify an impact on the device performance. In general, the setup is neither limited to a specific illumination wavelength nor to micro-mirrors as structures under test

The package of a Micro-Opto-Electro-Mechanical System (MOEMS), a Micro Mirror Array (MMA) based Spatial Light Modulator (SLM), has to stay stable over the full operation temperature range and throughout SLM lifetime in spite of the inevitably different coefficients of thermal expansion (CTE) of the various materials involved. Additionally, in our case the window not only protects the MMA from mechanical damage and corrosion but also serves an optical function as part of a beam combiner. Within the European Union funded Project REALHOLO we are therefore developing a packaging concept that accomplishes the desired optical functionality while meeting the challenge of precise alignment of the window relative to the micro mirrors in lateral direction, which is the motivating factor behind the FEM simulations presented here. The objective of this research is to stabilize the package when subjected to temperature changes by simulating its thermomechanical behaviour with Ansys Workbench TM . A heatsink, a silicon crystal-based MEMS chip, and a window are glued together to form the package. Materials used for window and heatsink components, respectively, are chosen for a best possible CTE match. The significant parameters to be considered for package optimization are the misalignment between window and chip, the stress induced in the package, especially the glue, and the global deformation of the MMA surface. This paper discusses the challenges and possible solution based on a series of simulation findings.