A variety of different photo resists are used for fabrication of MEMS. Presently good results were reported for SU-8, a chemically amplified negative tone photoresist. But SU-8 has a disadvantage for some applications in LIGA technique, especially in the X-ray mask fabrication. After processing the finished resist pattern are hardly soluble from the substrate. This paper will briefly describe the current status of the development of the new negative tone photoresist CAR 44 whose big advantage is the easy removableness of the cross linked pattern.

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The high suitability of hydrogen silsesquioxane (HSQ) as e-beam resist has long been known. Despite its undoubtedly good and reliable properties, HSQ nevertheless proves to be problematic in certain aspects due to its relatively short shelf-life and the small processing window between coating preparation and exposure. We thus intended to optimize the silsesquioxane with respect to a prolonged shelf-life and larger processing window while retaining all advantages like the high silicon content for high etch resistance and high pattern resolution. Our combined knowledge resulted in the development of the hydrogen silsesquioxane-based e-beam resist Medusa 82 with improved characteristics. Medusa 82 can be processed with HSQ standard procedures but allows for a delay of several weeks between layer preparation and exposure under standard conditions. Medusa 82 resist compositions tolerate storage periods of several weeks at room temperature. In addition, we generated and investigated variants of Medusa 82, which offer the possibility for exposure with less energy to cross-link the resist. Furthermore, weaker alkaline developers can be applied. A postexposure bake of these new Medusa 82 variants provides a significant enhancement of sensitivity and contrast. In this context, applications of Medusa 82 in deep to extreme ultraviolet and grayscale lithography are described. The use of glasslike resists with moderate electron beam sensitivity has the potential to reduce the effort and to simplify the manufacturing process of micro-optical devices that traditionally have to be structured in glass surfaces. The transformation process of Medusa 82 into a glasslike material involves an e-beam exposure, a thermal treatment, or a combination of both. Moreover, the adjustable contrast and sensitivity enable grayscale lithography. Different e-beam exposures trigger a different cross-linking degree within the layer, resulting in height variations after development. A postexposure bake step induces further cross-linking and a complete conversion into silicon oxide.

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