Development of optimum annular illumination: a lithography-TCAD approach

The development of advanced steppers with adjustable numerical aperture, and size and shape of the illumination source enables us to improve resolution with less depth-of-focus penalty. However, the optimization of lithography processes for this type of illuminators is costly due to its high complexity. In this paper, we propose an efficient methodology to optimize the process window for an annular illumination stepper through using litho-TCAD and experimental data. This paper demonstrates the calibration of litho-TCAD to experimental profiles and the use of Taguchi optimization to select the best choice of numerical aperture, inner coherence and outer coherence