Anisotropic EUV flare measured in the engineering test stand (ETS)

Abstract

We demonstrate direct flare measurements of the 4-mirror projection optics in the Engineering Test Strand (ETS). By using a conventional resist clearing method, also called the Kirk method, flare was directly measured in the ETS. Although flare has been verified to be constant across the field in our study, different flare values have been observed in different directions. The flare anisotropic variation makes flare compensation more complicated, and it may even result in non-uniform CD changes in different directions. In order to fully identify the directional flare variations of the projection optics in the ETS, a special flare measurement feature, a spoke pattern, has been created. The spoke pattern has been used to measure flare in azimuthal directions (every 15 degrees), and rigorously measured flare in all directions is presented in this study. Measured flare is highest in horizontal direction and lowest in vertical direction. The azimuthal flare variation is believed to be due to anisotropic mirror polishing. Measured flare in all directions qualitatively agrees with the polishing signatures of individual mirrors in the measured optics.

Effects of Flare on Latent Image Formation in Chemically Amplified Extreme Ultraviolet Resists

“…[3][4][5] The intensity of flare has been evaluated for many exposure tools. [5][6][7][8][9][10][11][12][13][14] Owing to recent developments, flare intensity has been reduced. However, the flare intensity remains high (5 -10%).…”