Reiji Sano

Optical Properties of NaF Single Crystals in VUV Region

The results of the reflectivity and absorption measurements on NaF single crystals (Harshaw) at 78°K and at room temperature are presented. The fluorine doublet, and the side band structure which is located at the higher energy side of the former and is presumably due to the transition of simultaneous creation of exciton and phonon, are observed in the reflectivity spectrum at 78°K. The spectra of optical of constants derived from these reflectivities by means of the Kramers-Kroning relation are also presented. It is shown that the fluorine doublet can be decomposed into two asymmetric Lorentzian lines with the oscillator strengths 0.155 and 0.215 for the lower and higher energy components, respectively. The position of the first reflectivity peak of ( 2 S 1/2 , 2 P 2/3 ), determined in the temperature range of 10°K to 295°K, is found to be well fitted by the formula of Bose-statistics. The empirical relation which is capable of representing the thermal shift of the first exciton peak of all alkali halide...

Ionic Conductivity in KCl and Its Dependence on Electrodes

It has been pointed out that the d.c. as well as a.c. conductivity measurements with alkali-halide crystals are liable to be affected by the nature of the electrode employed. In the present study, a number of electrode materials were examined in this regard, especially for use with KCl. Carbon electrodes prepared by vacuum deposition were found to be satisfactory in that (i) contamination from electrodes through thermal diffusion was undetectable at least microscopically, (ii) the measured conductivity showed reproducible changes when the specimen temperaure was varied, and (iii) the d.c. and a.c. conductivity values agreed with each other. Using the carbon electrodes, the dielectric constant of KCl in the kilocycle region was determined in the temperaure range 236°–522°C.

Study of Hydrogen Vacuum-Ultraviolet Light Sources for Submicron Lithography

The output properties of hydrogen light sources and the resist parameters, such as spectral sensitivity and absorption coefficient, in the vacuum-ultraviolet (VUV) region were investigated. A very low exposure energy of about 1 mJ/cm2 was obtained by employing a very thin polymethyl methacrylate film and the VUV light of hydrogen microwave discharge. Contact photolithography using a Si/MgF2 mask and a trilayer resist system showed that submicron patterns as small as 0.2 ?m had been replicated at an exposure time of under 30 s.

Narrow-Band KrF Excimer Laser -- Tunable And Wavelength Stabilized

A tunable and wavelength stabilized KrF excimer laser has been developed. Two Fabry-Perot etalons of 2.4 THz and 170 GHz FSR are placed inside of the laser cavity to reduce the lasing bandwidth to 0.003 nm (3 pm). The wavelength was found to be tunable over a range from 248.1 nm to 248.6 nm. Within this tuning range, a stable wavelength setting to ±0.5 pm was achieved with a feedback system composed of a wavelength detector and a controlling mechanism. This wavelength-stabilized tunable KrF excimer laser will find its applications in optical microlithography, plasma diagnostics and photochemical reactions.

Nanometer Pattern Transfer by VUV Lithography with a D2 Lamp

Vacuum-ultraviolet lithography of a trilayer resist system which consists of polymethyl methacrylate (PMMA), Si and polyimide has been studied using a deuterium lamp. The exposure dose needed for a 0.1-µm-thick PMMA film is less than 1 mJ/cm2, and a high etch rate ratio of 40 for polyimide to Si is obtained with the reactive ion beam etching (RIBE) technique. Using a simple contact exposure system and RIBE, photomask patterns are accurately transferred in the polyimide down to a linewidth of 0.2 µm, and 50-nm line patterns of polyimide are obtained.