A Micro Racetrack Optical Resonator Test Structure to Optimize Pattern Approximation in Direct Lithography Technologies

High-throughput electron beam (EB) lithography technologies such as variable shape beam (VSB) and character projection (CP) are drawing much interests to the industries due to the wafer scale exposure capability and reduced exposure time in the order of magnitude. However, the tradeoff relationship of the exposure quality according to the EB exposure pattern approximation methods has not yet been comprehensively studied. The study is essential for photonics because target patterns include curved shapes. We propose a test structure of silicon racetrack resonator to quantify the quality dependence. Three approximation techniques were tried such as octagon shape CP, tilted square CPs, and thin variable shape rectangles. Optical measurement clearly revealed quality differences between methods, which were impossible to be identified by classical metrological methods including Surface Probe Microscopy (SPM).