Translator Disclaimer
21 May 1996 Effect of variable sigma aperture on lens distortion and its pattern size dependence
Author Affiliations +
While modified illumination with various illumination apertures is the promising method to get finer patterns, there are many problems in putting it into practical use. In particular, the different apertures give different effects on the lens distortion and they cause the pattern displacement. In this paper, we studied the image placement error of fine patterns under 1 micrometer and its pattern pitch dependence using various illumination apertures. The first layer of 0.8 micrometer lines and spaces is patterned using conventional aperture (NA equals 0.57, sigma equals 0.6) and the second layer is exposed on the etched patterns with various apertures such as conventional, annular and small sigma. The patterns of the second layer are 0.4 micrometer lines with various spaces. Pattern displacements of the second layer are measured within the lens field along the X axis. The results show that the displacements are affected by the illumination status. In addition, the displacement varies with the pattern pitch and the placements of the fine patterns are different from those of large overlay patterns such as box-in-box. These results are confirmed by the optical simulator. The simulated results correspond to the experimental results and they point out the third order coma aberration most effects the pattern displacement. The pattern size and pitch dependence of the image displacement reveals that the measurement result of the conventional overlay patterns such as box-in-box with the sizes of 10 - 20 micrometer doesn't represent the overlay of the fine patterns of actual devices.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Takashi Saito, Hisashi Watanabe, and Yoshimitsu Okuda "Effect of variable sigma aperture on lens distortion and its pattern size dependence", Proc. SPIE 2725, Metrology, Inspection, and Process Control for Microlithography X, (21 May 1996); doi: 10.1117/12.240102;

Back to Top