Tokuyuki Honda

Mask optimization for arbitrary patterns with 2D-TCC resolution enhancement technique

In this paper, a new resolution enhancement technique named 2D-TCC technique is proposed. This method can enhance resolution of line patterns as well as that of contact hole patterns by the use of an approximate aerial image. The aerial image, which is obtained by 2D-TCC calculation, expresses the degree of coherence at the image plane of a projection optic considering mask transmission at the object plane. OPC of desired patterns and placement of assist patterns can be simultaneously performed according to an approximate aerial image called a 2D-TCC map. Fast calculation due to truncation of a series in calculating an aerial image is another advantage. Results of mask optimization for various line patterns and the validity of the 2D-TCC technique by simulations and experiments are reported.

Extension of the 2D-TCC technique to optimize mask pattern layouts

The extendibility of 2D-TCC technique to an isolated line of 45 nm width is investigated in this paper. The 2D-TCC technique optimizes mask patterns placing assist pattern automatically. For 45 nm line patterns, the assist pattern width generally becomes much smaller than the exposure wavelength of 193 nm. Thus, the impact of the topography of a mask is examined using an electro-magnetic field (EMF) simulation. This simulation indicates that unwanted assist pattern printings are brought about by assist patterns with a smaller size than expected by the Kirchhoffs approximation. The difference, however, can be easily solved by giving a bias to the main pattern in the optimized mask. The main pattern bias decreases DOF very little. Furthermore, DOF simulated with a thick mask model is roughly the same as that simulated with a thin mask model. Therefore the topography of the optimized mask does not have an influence on the assist pattern position of the optimized mask. From these results, we have confirmed that the 2D-TCC technique can be extended to the optimization of 45 nm line patterns. As one of the notable features, the optimized aperiodic assist pattern greatly reduces MEEF compared with the conventional periodic assist pattern. To verify the feasibility of the 2D-TCC technique for 45 nm line, we performed experiment with an optimized mask. Experimental results showed that DOF increased with the number of assist pattern as simulation indicated. In addition, a defect whose length was twice that of the assist pattern did not have an influence on CD. From these results we have confirmed that the 2D-TCC technique can enhance the resolution of 45 nm line and has practical feasibility.

Hexagonal pattern formation due to counterpropagation in KNbO3.

We report the transverse instability of laser beams due to counterpropagation in photorefractive KNbO3. Hexagonal unstable emission emerges around two counterpropagating pump beams. This emission is in the same linear polarization with the pump beams and is observed in configurations where reflection gratings are dominant.

High-accuracy length-measuring interferometer using the two-colour method of compensating for the refractive index of air

A high-accuracy length-measuring two-colour interferometer for the compensation of the refractive index of air is described. It counts two types of interference fringes which are in phase quadrature by means of a lambda /8 plate. The light source is a diode laser pumped YAG laser of about 40 mW output power; its second harmonic wave is generated by a KTiOPO4 (KTP) crystal. The resolution in determining the refractive index of air is improved by averaging the numbers of the interference fringes counted. The interferometer is evaluated to be better than 2*10-7 in accuracy.

Optical Measurement of Ultrasonic Nanometer Motion of Rough Surface by Two-Wave Mixing in Bi12SiO20

Motion of a rough surface of an ultrasonic transducer was measured using an optical interferometer based on photorefractive two-wave mixing in a Bi12SiO20 crystal. The displacement equivalent to noise was 0.10 nm in a band-width of 8.0 MHz. The low-frequency noise was automatically compensated by an adaptive property of the photorefractive grating without an electric feedback loop.

Threshold for spontaneous pattern formation in reflection-grating-dominated photorefractive media with mirror feedback

A theoretical analysis is presented of spontaneous pattern formation in a system consisting of a photorefractive medium and a feedback mirror. A threshold condition for the pattern formation is derived from a new set of coupling equations with the assumption that reflection gratings are dominant. It is shown that the pattern formation can occur with only energy coupling. The direction of the sideband beams is calculated as a function of the mirror position, and the result is compared with that of an experiment with a KNbO(3) crystal.

One-color one-beam pumping of Er(3+)-doped ZBLAN glasses for a three-dimensional two-step excitation display.

We demonstrate a one-color one-beam pumping method for a three-dimensional two-step excitation fluorescent display with Er(3+) -doped ZBLAN glass. A localized green fluorescent spot is obtained by use of a focused pump-light beam at 979 nm. The quantum efficiency of the two-step excitation fluorescence is investigated in a time-dependent analysis and an experiment with a pulsed pump light.

Flow and controlled rotation of the spontaneous optical hexagon in KNbO(3).

The flow and rotation of the optical hexagonal pattern spontaneously formed in a photorefractive KNbO(3) crystal is studied. It is demonstrated that the direction and speed of rotation can be controlled with an additional erase laser beam.

Buildup of spontaneous hexagonal patterns in photorefractive BaTiO3 with a feedback mirror.

Spontaneous formation of optical patterns is demonstrated in a system consisting of a BaTiO3 crystal and a feedback mirror. The buildup and the dependence on the feedback path length of the patterns are described. A possible mechanism of the pattern formation is discussed.

Two-photon holographic recording in aluminosilicate glass containing silver particles.

Recording of holographic gratings by 532-nm laser pulses in photochromic bulk aluminosilicate glass containing silver particles is demonstrated. A diffraction efficiency of 1.5% is achieved for readout at the same wavelength. The speed of grating formation as a function of pulse energy suggests that two-photon excitation is responsible for the recording. The light causes bleaching of an absorption peak near 417nm, which corresponds to the excitation of surface plasmons on the silver, and broad darkening throughout the visible to the near infrared. A likely mechanism for the photochromic effect is discussed.