2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

Optimization of Masks for High Aspect Ration UV-Lithographic Patterning

U. Triltsch and S. Büttgenbach
Technische Universität Braunschweig, DE

Frenel diffraction, evulutionary algorithms, electro-depositable resist, UV-lithography

The increasing complexity of micro actuators and micro sensors (e.g. electroplated micro coils, flux guidances, insulation and planarization layers) make new fabrication technologies and materials inevitable. For such purposes thick-film photo resists like SU-8 or AZ9260 enable the fabrication of high aspect ratio 3D structures. Electro-depositable photo resists (ED) have been successfully used to coat arbitrary geometries. The main difficulty of this technology exists in the different levels of the microstructures and substrate which results in a proximity distance, where diffraction effects distort the original mask structure. This paper reports on how the simulation of the high aspect ratio UV-lithography process is coupled to an evolutionary optimization algorithm in order to derive a suitable mask structure for a given design problem. Inside the main iteration loop an individual, represented by a mask layout, is manipulated in the manner of a DNA string evolving over generations. The simulation tool is used to asses the quality of each layout. Each layout is simulated and the result is compared by an exclusive-or of the resulting intensity plot with a reference bitmap. Depending on the resulting score a layout is either removed from the optimization process or selected for the next generation. Recombination of the selected individuals on the one hand and mutation on the other hand are used to derive new layouts.

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