Advances in SLM Development for Microlithography

The Fraunhofer IPMS, in cooperation with Micronic Laser Systems, develops and fabricates micromirror arrays used as spatial light modulators (SLM) for image generation in microlithography. The SLMs used consist of 2048x512 individually addressable micromirrors of 16x16 mu m(2) and can be operated in an analog mode at a frame rate of up to 2 kHz. There are continued efforts to improve the performance of the mask writers with respect to stability and CD uniformity, which include measures to improve the SLMs used, especially with respect to the optical quality and the stability. Therefore, a new technology has been introduced which allows to use different materials for the mechanical suspension and the mirror, thus optimizing them separately. The hinges are made of a thin layer of a material with very good creep resistance, while the mirrors consist of a thick aluminium alloy with high reflectivity in DUV. Furthermore, the same inorganic material is used for the planarization of the electrodes (by means of chemical mechanical polishing) and as sacrificial layer for the actuator fabrication. Thus, at the end of the process, all sacrificial material, including that between the electrodes is removed. In this way, the charging effects caused by dielectrics between the electrodes (as seen in the previous devices) are eliminated. The first devices using the technology described above have been fabricated and tested. The first tests in a lithography machine show that considerable improvements in machine performance can be expected. The next steps are to stabilize and optimize the process.