E-Beam Lithography Stencil Planning And Optimization With Overlapped Characters

Electronic Beam Lithography (EBL) is an emerging maskless nanolithography technology which directly writes the desired circuit pattern into wafer using e-beam, thus it overcomes the diffraction limit of light in current optical lithography system. However, low throughput is its key technical hurdle. In conventional EBL system, each rectangle in the layout will be projected by one electronic shot, through a Variable Shaped Beam (VSB). This would be extremely slow. As an improved EBL technology, Character Projection(CP) shoots complex shapes, so called characters, by putting them into a pre-designed stencil to increase throughput. However, only a limited number of characters can be put on the stencil due to its area constraint. For those patterns not in the stencil, they still need to be written by VSB. A key problem is how to select an optimal set of characters and pack them on the CP stencil to minimize total processing time. In this paper, we investigate a new problem of EBL stencil design with overlapped characters. Different from previous works, besides selecting appropriate characters, their placements on the stencil are also optimized in our framework. Our experimental results show that compared to conventional stencil design methodology without overlapped characters, we are able to reduce total projection time by 51%.