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9 November 2001 Requirements and approaches to adapting laser writers for fabrication of gray-scale masks
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The photolithography using gray-scale masks (GSM) with multilevel transmittance is now one of promising ways for manufacturing of high efficiency diffractive optical elements and microoptics. Such masks can be most effectively fabricated by laser or electron-beam writers on materials with a transmittance changing under influence of high-energy beams. The basic requirements for adaptation of existing and developed scanning laser writers are formulated. These systems create an image by continuous movement of a writing beam along one coordinate and overlapping of adjacent written tracks along another coordinate. Several problems must be solved at the GSM manufacturing: the calibration of the influence of the laser beam on a recording material without transferring the gray-scale structure into photoresist; the transmittance at the current exposed pixel depends on surrounding structures generated before recording of the current track and a character of the laser beam power modulation; essential increasing of the computed data in comparison with binary elements. The offered solutions are based on the results of investigations of the materials with variable transmittance (LDW-glass, a-Si film) and takes into account the specificity of diffractive blazed microstructures. The reduction of data amount for fabrication of multi-level DOEs is effectively performed using offered vector-gradient data format, which is based on piecewise-linear approximation of phase profile. The presented approaches to adaptation of laser writers are realized in software and hardware, and they allow to solve the basic problems of manufacturing GSMs.
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Victor Pavlovich Korolkov, Ruslan Shimansky, Alexander G. Poleshchuk, Vadim V. Cherkashin, Andrey A. Kharissov, and Dmitry Denk "Requirements and approaches to adapting laser writers for fabrication of gray-scale masks", Proc. SPIE 4440, Lithographic and Micromachining Techniques for Optical Component Fabrication, (9 November 2001);

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