Kiyoshi Uchikawa

Angular spectrum calculations for arbitrary focal length with a scaled convolution

Nyquist sampling theorem in an image calculation with angular spectrum method restricts a propagation distance and a focal length of a lens. In order to avoid these restrictions, we studied suitable expressions for the image computations depending on their conditions. Additionally, a lateral scale in an observation plane can be magnified freely by using a scaled convolution in each expression.

Phase-modulation technique for accumulated photon echo

A novel photon-echo technique based on the phase-modulation method has been developed that is applicable to the accumulated photon echo in scattering materials.

Photon-echo spectroscopy on biological systems. I. Application to tissues

The fluorescence detection technique of incoherent accumulated photon echo is applied to the investigation of animal and human tissues. The correlation between the kind of animal tissue and the dephasing time is determined. The dephasing times of normal and cancerous human tissues are measured by this technique. The cancer tissues exhibit shorter dephasing times than the normal tissues, and this is interpreted as being caused by the large number of conformational substates of cancer tissues. The dephasing time of a benign-tumor tissue is also measured and shows a value similar to that of the normal tissue. The dephasing time of a metastasizing cancer region is also measured. The applicability of photon-echo spectroscopy to diagnosis is noted.

Method for designing phase-calculation algorithms for two-dimensional grating phase-shifting interferometry

We propose a design method of phase-analysis algorithms based on two-dimensional grating phase shifting for Talbot interferometry, Talbot-Lau imaging, or the Ronchi test. These algorithms are designed to separate the two orthogonal shearing wavefronts and eliminate error effects of unwanted diffraction orders, simultaneously. Taking the effect of multidiffraction into account, moving the two-dimensional grating along a certain pass leads to a series of phase-shifted interfrograms, from which two orthogonal shearing wavefronts are derived, for the tested wavefront to be retrieved. The designing process is demonstrated, and the residual errors are analyzed via simulation works and experimental comparison.

Investigation of proximity effect correction in electron projection lithography (EPL)

An electron projection lithography (EPL) system which projects reticle patterns onto a wafer will be applied to sub 100 nm lithography. Requirements for line width accuracy are very strict as feature sizes are less than 100 nm. For electron beam lithography, proximity effect corrections have always been an important issue for accurate feature width control. In this paper characteristics of several correction methods are examined, and appropriate correction methods for 100 kV EPL are introduced. Employing the shape correction method burdens the reticle pattern preparation system much more than other methods. Therefore a calculation method suitable for 100 kV EPL where the backscatter radius is very wide ((beta) b approximately equals 30 micrometer) and the forward scatter radius is narrow ((beta) f approximately equals 7 nm) has been developed. The calculation of deposition energy by the backscattered electron beam is carried out with a coarse grid but wide range. The calculation of the combined effect of the electron scattering blurs from the features is carried out only within a narrow range. The correction calculation is carried out using both of these results. Using this method, accurate and fast calculations can be achieved. Employing the GHOST correction method increases total exposure cost. The practical GHOST correction methods may also be improved. An additional correction method named shape correction with GHOST is also shown.

Photochemical hole burning by photoinduced electron transfer. Effects of sacrificially consumable molecules

Abstract Photochemical hole burning by photoinduced electron transfer was studied with emphasis on the effects of sacrificially consumable molecules. A backward electron-transfer process reduces the total efficiency of electron transfer. In order to enhance the effective electron transfer and to suppress the backward electron transfer, sacrificially consumable molecules were introduced to the donor—acceptor electron-transfer systems. In the presence of sacrificially consumable molecules, the efficiency of hole formation increased remarkably. The two-color enhancement of hole formation was also observed for a suitable acceptor.

Error analysis and compensation method of focus detection in exposure apparatus

An original approach to measurement accuracy of a typical focus sensor in conventional integrated circuit lithographic equipment is introduced. Causes of measurement error in the focus sensor are theoretically analyzed and found to be generated mainly from interactions between imperfections of the optical system and the actual surface of processed wafers. We derive mathematical formulations describing these errors, which are confirmed by the experimental results performed by using an optical setup composed of the focus sensor and samples on which the wafer surface condition is reproduced. Furthermore, several novel techniques that are intended to reduce those measurement errors are successfully demonstrated.

Absolute surface profilometry of an object with large gaps by means of monochromatic laser interferometry

We propose a technique for monochromatic laser interferometry capable of absolute surface profilometry of an object with large height gaps exceeding a half wavelength. The technique does not use a broadband source, such as a low-coherence or multi-wavelength source, or a wavelength-tunable device, which causes a dispersion problem. Instead, we make use of the phase change of monochromatic light through the angular shift of illumination introduced by tilting the optical axis of the interferometer. For oblique illumination at angle θ, the phase difference between the test and reference surfaces separated by distance d is given by ΔΦ = 2kd cosθ , where k = 2π /λ is a wavenumber. In effect, the change of illumination angle θ functions as the change of wavelength λ . Therefore, while using a monochromatic laser light source, we can realize the same effect as a multi-wavelength source. From the relation between the illumination angle and the phase change, the absolute distance d between the test and reference surfaces can be determined without ambiguity of an integer multiple of a half wavelength associated with monochromatic interferometry. The large gap height can be determined also without ambiguity from the change of the absolute distance d across the boundary of the gap. Because the resolution of the absolute distance measurement by means of illumination angle change is not high enough by itself, we enhance the resolution by the following procedure. We first estimate the gap height to an integer multiple of a half wavelength by tilting the optical axis. Then the fractional portion of the phase is measured by setting the optical axis perpendicular to the test surface as in conventional interferometry. By combining the integer and the fractional portion, we can determine the absolute gap height with high accuracy and a large dynamic range exceeding a half wavelength. We present an experimental demonstration with a traditional Twyman-Green interferometer, in which a He-Ne laser was used as a monochromatic light source, and a test surface with a ~0.1 mm height gap was formed by two block gauges attached to a flat surface. The repeatability for five measurements was found to be as high as 0.1nm (in 1 sigma).

Accumulated photon-echo spectroscopy for stained tissue samples

We performed phase relaxation-time measurements of the accumulated photon echo for normal and cancerous tissue samples of human liver, that were stained with several kinds of dye. Each dye interacted selectively with a specific kind of biomolecule in the tissues, for example, DNA, proteins, or lipids. The cancerous tissues showed a tendency to have shorter relaxation times than the normal tissues had. The difference of relaxation time observed between the normal and the cancerous tissues depended on the dyes that were used for staining, and the difference became most clear when the tissues were stained with a cyanine dye derivative, i.e., YO-PRO3 Iodide, which has a high selectivity for DNA. We performed the relaxation-time mapping of the accumulated photon echo (photon-echo imaging) for a liver tissue sample stained by YO-PRO3 Iodide. The photon-echo imaging was successful in showing a region of a highly differentiated hepatocellular carcinoma in the tissue sample, while fluorescence-intensity mapping could not identify the cancerous region in the same tissue sample. These results indicated a possibility that the reduction of accumulated photon-echo relaxation time observed in the cancerous tissues was caused by a change of microscopic dynamics of DNA.

Femtosecond optical memory with an incoherent light source

The time resolution in the photon echo memory has been improved significantly by using a broadband incoherent light and the heterodyne detection of the photon echo. The time resolution has reached almost the limiting value which is determined by the inhomogeneous spectral width of the hole burning material. With the use of a digital optical delay line, the optical data has been retrieved with a high signal-to-noise ratio.