Hiroaki Aritome

Soft x‐ray spectra of highly ionized elements with atomic numbers ranging from 57 to 82 produced by compact lasers

X‐ray emission spectra in the spectral range of 2–13 nm from 19 kinds of material with high atomic numbers (lanthanum through lead) were recorded with a grazing incidence spectrometer equipped with a microchannel plate detector. There is an intense, narrow spectral band in these spectra which shifts toward shorter wavelength and becomes weak in intensity with increasing atomic number. The materials were irradiated either by a 4 J/35 ns slab Nd:glass laser or by a 0.5 J/8 ns Nd:YAG laser. The absolute photon intensities of the spectra were determined with an absolutely calibrated charge coupled device camera. The peak spectral brightness of the emission at the peak intensity of the spectral band for lanthanum plasma was estimated to be 2.1×1016 photons/s/mm2/mrad2 in 0.1% bandwidth. The origin of the narrow, intense spectral bands in the recorded spectra and their dependence on target materials and laser wavelength are interpreted.

Zone-plate X-ray microscope using a laser plasma source

An imaging X-ray microscope using a laser plasma X-ray source, an objective zone plate and an ellipsoidal condenser mirror with multilayer coating is described. The 3.37 nm line emission from a carbon plasma is filtered and focused by the ellipsoidal condenser mirror and used as a light source. A magnified image (magnification: ×287) of a gold zone plate was obtained by a back-illuminated charge coupled device (CCD) whose pixel size is 22 µm×22 µm. The 0.4-µm-period pattern (outermost zones: 0.27 µm line and 0.13 µm space) is clearly resolved.

Microfabrication of LiNbO3 by Reactive Ion-Beam Etching

The ratio of the etching rate of LiNbO3 to AZ1350 at normal incidence for CHF3 ion is about 5 times as large as that for Ar ion. This high ratio is utilized to fabricate LiNbO3 blazed gratings and also LiNbO3 guided wave optical elements such as grating couplers to demonstrate that reactive ion-beam etching is a very useful microfabrication technique for LiNbO3.

Water window x-ray source produced by a slab glass laser

X‐ray emission in the water window spectral region (2.3–4.4 nm) from materials (carbon, aluminum, titanium, copper, and molybdenum) irradiated by a 5 J/35 ns slab glass laser was recorded with a grazing‐incidence spectrometer for microscopy application. Carbon was determined to be the suitable source material for an x‐ray microscopy experiment. The absolute spectral brightness of the CVI 1s‐2p line and CV 1s2‐1s2p line emitted from the carbon plasmas was estimated to be ∼1.0×1016 photons/s/mm2/mrad2 in 0.1% bandwidth. The electron density and electron temperature of the carbon plasmas were derived from the x‐ray spectra and the conditions for intense emission are also discussed.

Fabrication of a Grating Pattern with Submicrometer Dimension in Silicon Crystal by Ion-Bombardment-Enhanced Etching

Ion-bombardment-enhanced etching (IBEE) as a means for fabrication of submicron pattern is described. Electron beam lithography and lift-off technique are used to form a Cr mask pattern for ion-bombardment. The etched depth can be controlled from 83 to 128 nm by varying the ion dose with an accuracy of 10 nm. A grating pattern with a period of 0.6 µm is fabricated in a Si substrate by IBEE technique by using Ar+ ion. At an Ar+ ion energy of 60 keV, the amount of side etching is observed to be 40 nm for a 0.21-µm deep etched sample. This result shows the high resolution of IBEE.

Reactive Ion-Beam Etching of Silicon Carbide

A reactive ion-beam etching technique using freon gas is developed for microfabrication in SiC. The enhancement of the etching rate of SiC is apparent by admixing O2 gas in CF4 gas. The etching rate of SiC for CF4+O2 (40%) gas is about 2 times larger than that for Ar gas. This technique appears to be very useful for producing various devices of SiC.

X-ray diffraction gratings for synchrotron radiation spectroscopy: a new fabrication method

Silicon dioxide lamellar gratings fabricated by a new technique combining holographic exposure and reactive ion-beam etching are found experimentally to be appropriate to and useful for synchrotron radiation spectroscopy. Methods to improve edge roughness and to control the land-to-groove width ratio are also investigated. The fabrication technique developed here is relatively simple in comparison with the ruling technique which needs delicate control. Therefore, it is a promising way to employ these bakable original gratings for synchrotron radiation spectroscopy.

High repetitive plasma x‐ray source produced by a zigzag slab laser

Some properties of laser‐generated plasma emission in the soft x‐ray region (0.1 keV<hν<1.5 keV) are presented. Detailed spectral distributions are reported for several kinds of materials (carbon, aluminum, titanium, copper, zinc, molybdenum, tin, tungsten, and lead). Dependence of x‐ray emission on focal size and target thickness is also studied. The experiments were carried out at a laser intensity of a few times 1012 W/cm2 using Nd‐doped phosphate zigzag glass slab laser (8 J/40 ns, λ=1.054 μm). As an application of the laser‐generated plasma x rays, the sensitivity of FBM‐120 resist for x‐ray lithography was measured and a 0.25‐μm‐wide space mask pattern was replicated.

Graphoepitaxy of Ge Films on SiO2 by Zone Melting Recrystallization

Graphoepitaxy of vacuum-evaporated Ge films on amorphous fused quartz or thermally grown SiO2 substrates with surface-relief gratings engraved by reactive ion etching has been performed by a heating process of zone melting. We observed that zone melted films on gratings consisted of grains of 2–10 µm size with direction parallel to the grating axis and perpendicular to the substrate plane.

X-ray Replication of Masks by Synchrotron Radiation of INS-ES

Synchrotron radiation has been used for X-ray lithography. At an electron energy of 1. 1 GeV, o.4 µm gold layer on 3 µm silicon membrane was sufficient for obtaining good contrast in PMMA for direct SOR total beam. By using the mask of the gold grating pattern with 692 nm period made by holographic method, the grating pattern with a large height-to-width ratio of very narrow line (2.2 µm: 0.2 µm) is obtained in PMMA. This result clearly demonstrates the high collimation of X-ray beam from the synchrotron. Effects of diffraction are observed in replicated patterns when a mask and a wafer are separated and are well explained by the theory of Fresnel diffraction as a function of the slit width, the wavelength and the distance between a mask and a wafer.