Reduction of the absorber shadow effect by changing the absorber side wall angle in extreme ultraviolet lithography

The near-field intensity on the extreme ultraviolet lithography (EUVL) mask and the aerial image on the wafer are affected by the mask structure. The absorber and the buffer layer make a shadow since the light is shining on the mask at some angle to the normal on-axis. This shadow effect in the EUVL mask is an important factor that decreases the contrast of the aerial image and, as a result, causes a line width variation and a pattern shift. The thickness and the structure of the absorber stack affect the mask shadowing. The optimum structure of an EUVL mask to decrease the shadow effect is researched and reported. Among the several possible mask structures, we focused on the mask edge slope variation with a typical incident angle of 5 degrees. This modification of the mask structure compensates for the shadow effect on the near-field intensity and the aerial image.