Predicting the lithography impact of a phase defect embedded in a mask used for extreme ultraviolet lithography on the printed image on wafer is a challenging task. In this study, two types of measurement tools were employed to characterize the phase defects. The prior measurement tool was a scanning probe microscope used for measuring the surface topography of phase defects, and the second was an at-wavelength dark-field inspection tool capable of capturing a phase defect and then calculating the defect detection signal intensity (DSI) from those images. A programmed phase defect mask with various lateral sizes and depths was prepared. The sizes and DSIs were then measured. The measured data indicated that the DSIs did not directly correlate with the phase defect volumes. The influence of the phase defects on the printed image on a wafer was also calculated using a lithography simulator. The simulation results indicated that the printed critical dimensions (CDs) were strongly correlated with the DSIs rather than with the phase defect volumes. As a result, the influence of the phase defect on the printed CD can be predicted from the values of the DSIs.
Amano and Abe: Measurement of the phase defect size using a scanning probe microscope and at-wavelength inspection tool