Coma measurement of projection optics in lithographic tools based on relative image displacements at multiple illumination settings

Abstract

In this paper, we propose a novel method for measuring the coma aberrations of lithographic projection optics based on relative image displacements at multiple illumination settings. The measurement accuracy of coma can be improved because the phase-shifting gratings are more sensitive to the aberrations than the binary gratings used in the TAMIS technique, and the impact of distortion on displacements of aerial image can be eliminated when the relative image displacements are measured. The PROLITH simulation results show that, the measurement accuracy of coma increases by more than 25% under conventional illumination, and the measurement accuracy of primary coma increases by more than 20% under annular illumination, compared with the TAMIS technique.

Parity decomposition theory of full wavefront aberration measurement using the intensity differences of aerial images in microlithography

“…Moreover, we have numerically shown the proof of concept of this method in practical aberration regions. The merit of WAMPD is that this measurement technique does not require best focus shift measurements, unlike the technique discussed in previous studies [2][3][4][5][6][7][8]. The applicable aberration region may be larger than that of previously proposed methods because the squared aberration terms are exactly canceled.…”

“…Moreover, we cannot apply interferometer measurements to the "lens-onbody" situation in which the projection optics have already been installed in the exposure apparatus. On the other hand, alternative methods based on images projected by the optical system, which are called aerial images in this work, have been actively suggested [2][3][4][5][6][7][8][9][10][11][12] and could be utilized in lens-on-body aberration measurements at the cost of the measurement accuracy.…”

“…For example, the odd aberration leads to a lateral shift of the total aerial image, and the even aberration shifts the best focus position in the z axis. Therefore, the wavefront aberration can be estimated by measuring the qualities of these aberration-induced characteristics [2][3][4][5][6][7][8]. However, in the measurement of the best focus shift, we must obtain at least three defocused images at different z-axis positions.…”

Coma measurement by use of an alternating phase-shifting mask mark with a specific phase width

“…Z 23 and the other higher coma terms remain low level in the projection lens [21]. The impact of distortion on the IPE can be eliminated when the relative image displacements are measured [22]. Even aberrations induce only shifts of best focus with no IPE when the exit pupil is illuminated symmetrically by use of the conventional, dipole, annular, quadrupole, and quasar illumination models.…”

Even aberration measurement of lithographic projection system based on optimized phase-shifting marks

“…Recently, we have reported several novel in-situ methods for measuring the wavefront aberration based on phase-shifting marks that had a line/space ratio of 1:1 [11][12][13]. However, the line/space ratio of the phase-shifting marks which obviously influences the sensitivity to even aberrations was not optimized, so the measurement accuracy of even aberrations can still be further improved.…”