Optimization of exposure parameters for direct laser writing in optical lithography

Various types of nano- and micro-structures, such as security holograms and diffractive optical elements, can be prepared directly into a photoresist using a direct-write optical lithography. Precise knowledge of photoresist properties, parameters of exposure, and photoresist development time are essential. We have characterized and optimised exposure of the positive binary sensitive photoresist ma-P 1200 series. Complex optical functions were obtained using Mueller matrix spectroscopic ellipsometry. True thickness profile of linearly exposed photoresist was studied by confocal microscopy and strong non-linearity was observed. In this paper we propose exposure correction to compensate this non-linearity.