Combined e-beam lithography using different energies

•E-beam grayscale lithography combining two systems with different energies•Throughput improvement of large-scale highly complex 3D micro-optical elements•Two methods presented - independent and simultaneous development process.

This paper considers the possibilities of combined exposure of e-beam systems working with a significant difference of primary electron energies (Gaussian beam system Raith EBPG5000 + ES - 100 keV, variable shape beam system Tesla BS600 - 15 keV) on one substrate with one resist layer for the purposes of grayscale lithography. Variation of primary electron energies and differences in e-beam systems make it possible to use each system for various parts of a large-scale pattern containing various micro-optical elements. The mix and match process can be carried out in two possible ways. The first method consists of two successive exposures followed by resist development. This method has the advantage of using only one developer, though it requires better control of proximity effect corrections. The second method is to perform exposures and resist development independently by finding a suitable second developer that does not influence the result of the first exposure. This method allows the tuning of the resulting structures from each system independently by adjusting the development process (temperature, time). We tested several parameters of both system exposures (data preparation, resolution, speed, type of patterns, developers) to show the advantages of using this combined technique for grayscale lithography. These methods make the preparation of highly complex large-scale micro-optical elements easier in comparison with the use of just one system.

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