Akihiko Sekine

Axial eye-length measurement by wavelength-shift interferometry

A simplified noncontact measuring technique for axial eye length was developed. According to this method, the wavelength shift of a single-mode laser-diode beam that is irradiated onto the eyeball causes a phase shift in the interference fringes of reflections from the retina and the cornea. Then the optical distance between the cornea and the retina is obtained from the phase-shift measurement. High-speed axial eye-length measurements can be performed by using a laser diode on a pulse-modulation drive and signals from the reference light path as an analog-to-digital-conversion trigger. Compared with the technique that uses partially coherent light, this technique is inferior in terms of measurement accuracy but superior in its wide, measurable range of 16-32 mm. The results of measurements of 21 adults showed that 2 standard deviations of measurement was 2 sigma = +/- 0.11 mm.

Advanced mask inspection optical system (AMOS) using 198.5-nm wavelength for 65-nm (hp) node and beyond: system development and initial state D/D inspection performance

A novel high-resolution mask inspection platform using DUV wavelength has been developed. This platform is designed to enable the defect inspection of high quality masks for 65nm node used in 193nm lithography. In this paper, newly developed optical system and its performance are reported. The system is operated at wavelength of 198.5nm, which wavelength is nearly equal to 193nm-ArF laser exposure tool. Some defect image data and defect inspection sensitivity due to simulation-base die-to-die (D/D) inspection are shown on standard programmed defect test mask. As an initial state D/D inspection performance, 20-60 nm defects are certified. System capabilities for 65nm node inspection and beyond are also discussed.

A New Method of Magnification Correction for Accurately Measuring Retinal Vessel Calibers From Fundus Photographs

Purpose To report a semiautomated retinal vessel caliber measurement system that measures central retinal artery (vein) equivalent (CRAE [CRVE]) with individual correction for magnification errors under conditions assuming optimal focus. Methods The focusing condition of the subject eye fundus camera optical system was individually determined by constructing an optical model of each eye applying its refractive error, corneal curvature, and axial length (AL) to Gullstrands schematic eye, and by adjusting the position of the cameras focusing lenses using each eyes refractive error. Once the focusing condition of the entire optical system was fulfilled, magnification of the fundus images was calculated using paraxial ray tracing. Measurements of CRAE (CRVE) were performed in an annular area centered on the optic disc with magnification-corrected diameter from 1.8 to 2.7 mm. Reproducibility of the measurements of the results using the new method and comparison with those using interactive vessel analysis (IVAN) were performed in normal Japanese eyes. Results Intra- and interexaminer intraclass correlation coefficient (ICC) for CRAE (CRVE) measurements was greater than 0.978. CRAE (CRVE) using the new method averaged 148.9 ± 10.9 μm (225.0 ± 13.9 μm; mean ± SD, N = 99). Differences between the new method and IVAN were greater with increasing AL (P < 0.001). The new method yielded CRAE (CRVE) in good agreement with IVAN in eyes with AL of approximately 24 mm. However, the new method yielded smaller values in eyes with shorter AL and vice versa. Conclusions A new accurate and reproducible method to measure CRAE (CRVE) from fundus photographs was reported.

Mask blank particle inspection in vacuum environments

The mask blank surface inspection system for the electron beam mask writing system (EB mask writer) has developed. This system, that has the small vacuum chamber attachable to EB mask writer, inspects a mask blank that is just before EB writing in vacuum environments. It can inspect whole area of the 230mm mask at 0.3micrometer sensitivity. It also can perform fast inspection by applying the original scanning algorithm for the laser beam. It has the wide detective range from 0.3 to 2.0 micrometers of particle size. It can distinguish sizes of particles in that range. The auto focus function is most important factor for maintaining the sensitivity.