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Waferstepper Alignment for MEMS Applications using Diffraction Gratings H. W. van Zeijl, K. Simon1, J. Slabbekoorn, W. v. Buel1 and C. Q. Gui1 Delft Institute of Microelectronics and Submicron technologies, Feldmannweg 17, 2628 CT delft, The Netherlands 1 ASM lithography, De Run 1110, 5503 LA Veldhoven, the Netherlands ABSTRACT MEMS manufacturing in general and the litho step in particular could benefit tremendously from an enhanced focus range of waferstepper alignment systems. This would help the MEMS community to cope with large substrate topography or extreme thick resist films. In this study the performance range over which of the alignment system of an ASML PAS5000/50 system operates has been investigated. A test device that requires bulk micro machining was designed and processed. The required front to backwafer alignment (FTBA) was performed on alignment markers in cavities etched through a 100mm wafer. On the test device the FTBA overlay was measured electrically as well as optically using the metrology capability of the stepper alignment system. The results obtained demonstrate the capabilities of an existing alignment system to deal with high topographies. The overlay errors observed were dominated by the bulk micro machining processing. INTRODUCTION The technology of Micro-Electro-Mechanical Systems (MEMS) refers to the integration of electronics, sensors, actuators and mechanical elements on a common silicon substrate. For the lithographic process steps as a part of the IC process sequence, a wafersteppers is generally employed. The high throughput and placement accuracy are also attractive for the MEMS lithographic production steps. However, with regard to the alignment, two issues arise when a waferstepper is employed in MEMS fabrication. First, the focal depth of the alignment system must match the high topography and/or extreme thick resist films often used in MEMS processing. If not, additional focussing is required which reduces throughput. Secondly, front-To-Back Alignment (FTBA), a key enabling technology for the fabrication of many MEMS devices, is not a standard feature on a waferstepper. In this work we explore the focal range of the alignment system of an ASML PAS 5000/50 waferstepper. The feasibility for MEMS applications is demonstrated on substrates with 520 µm topography. ALIGNMENT DETECTION SCHEMES Several categories of alignment detection schemes are used today; the most widely used are either based on contrast detection (brightfield/darkfield ) or phase grating diffraction schemes. These basic principles utilize the fact that light is a wave and carries therefore both phase and amplitude information. While the amplitude information is used for bright/dark field alignment systems, the grating alignment system extracts the phase information to perform alignment. The principle of brightfield /darkfield alignment systems is based on optical pattern recognition. A specifically designed alignment mark is illuminated by a light source, while a CCD camera U5.8.1 Downloaded from https://www.ca