Generation of trapezoidal illumination for the step-and-scan lithographic system

To meet the uniform dose exposure in optical lithography, it is desirable to get uniform illumination and trapezoidal illumination in the scanning direction on the wafer for the step-and-scan lithographic system. A design strategy for trapezoidal illumination is proposed which offers both high uniformity illumination and fixed integral energy of trapezoidal illumination in a different illumination pattern. The strategy describes a light uniform device which contains a microlens array, a microcylindrical array, and a Fourier lens and produces trapezoidal illumination directly at the scanning slit. Compared with the conventional method to obtain the trapezoidal illumination, the strategy in this paper reduces the difficulty of assembly and has the advantage of simplicity and directness without blocking energy. This method utilizes energy of the lithographic system more effectively, and it improves the throughput of the lithography. The simulation results show that this method not only maintains the uniformity of trapezoidal illumination but also improves the energy utilization.