The study of phase effects in EUV mask pattern defects

In this paper, we present a detail study of the impact of material-induced phase effect on the EUV mask absorber defect through-focus behavior. Illumination, material properties, and defect size are shown to have different impacts on the behavior. Also, we study the possibility of using alternative absorber materials to reduce the phase effects on the defect. Based on the mask near field distribution, energy confinement and phase accumulation can be reduced with new absorber materials. The defect sensitivity is reduced and the peak signal position is closer to the best focus due to less material-induced phase. Moreover, the novel pupil engineering method can utilize the phase induced by the material to improve the defect sensitivity of absorber defect by adding lens phase shifts in the pupil plane. At least 29% enhancement of the absorber defect signal at focus can be achieved by optimum lens phase shifts.