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Optical Nanolithography
Published in Bruce W. Smith, Kazuaki Suzuki, Microlithography, 2020
The advantage to using only a select portion of the lens pupil is appreciated when considering that those portions removed only add background energy to an image.The consequence is a reduction in image modulation. An additional advantage of OAI is a large depth of focus that can be gained by distribution diffraction energy only at radial locations of the projection lens pupil. This is shown in Figure 2.67, where the defocus OPD is shown together with the diffraction order energy for on-axis low sigma illumination and off-axis dipole illumination. In the on-axis case, a large defocus aberration effect will result in image blur because of the phase difference between the diffraction energy travelling through the center of the pupil and that travelling through the edge of the pupil. For dipole illumination, each pole distributes 0th and 1st diffraction order energy at radial pupil locations only. Because of this, there is little difference in the phase of all orders as they are collected by the lens pupil. The end result is imaging with significant improvement in DOF. Indeed, for poles that are single points, the DOF is infinite. More practical source sizes like those in Figure 2.66 may be necessary for throughput as well as the reduction in coherent image artifacts and the improvement will be lessened.
4-aperture differential image motion monitor as a new approach for estimating atmospheric turbulence parameters
Published in Journal of Modern Optics, 2019
B. Dibaee, R. Shomali, J. Khalilzadeh, A. Jafari, M. Amniat-Talab
In this study, the relation between the 4-aperture DIMM atmospheric defocus aberration (here after 4-aperture defocus) and the Fried parameter was evaluated. furthermore, the variance of the 4-aperture defocus was compared with those of Zernike defocus (13) and the differential image motion. Section 2 presents a brief overview of the 4-aperture DIMM. Section 3 is devoted to calculation of the power spectral density (PSD) of the atmospheric 4-aperture defocus. The relation between the variance of the 4-aperture defocus and Fried parameter is discussed in Section 4. The ability of estimating atmospheric coherence time by measuring the variance of the Zernike defocus velocity or the sum of the variances of two astigmatisms velocities was investigated in Section 5. Experimental analyses and results are presented in Section 6. Finally, concluding remarks are presented in the last section.