Kazuhiko Omote

Small angle x-ray scattering for measuring pore-size distributions in porous low-κ films

A small-angle x-ray scattering technique has been applied for characterizing pore-size distribution in porous low-κ dielectric films. The data are collected in reflection geometry using offset θ/2θ scans for avoiding strong specular reflections from the film surface and its substrate. The effects of refraction and reflection at the film surface and interface are corrected by the distorted wave Born approximation. A Γ-distribution mode is used to determine the pore-size distribution in a film. The technique has been used to analyze porous methyl silsesquioxane films. The pore sizes were found to disperse in the range from subnanometer to several nanometers, and the results agree well with those obtained by the N2 gas adsorption technique.

Crystallite size effect on the hole mobility of uniaxially aligned copper phthalocyanine thin-film field-effect transistors

We fabricated copper phthalocyanine (CuPc) thin-film field-effect transistors (FETs) with three different orientations of CuPc with respect to channels. The substrate rubbing treatment induced uniaxial orientation in CuPc layers, yielding higher hole mobility (∼0.02cm2∕Vs) than that of untreated FETs. Although the rubbing treatment bore high-aspect-ratio (>10) CuPc domains oriented to rubbing direction, the mobility anisotropy of the film was only 1.4. This discrepancy was explained by analyzing grazing-incidence x-ray diffraction profiles, i.e.: (1) In-plane mean size of crystals was smaller than their appearance in atomic force microscopy, and (2) the crystallites were much shorter in the apparent long-hand direction (11nm) than the direction perpendicular to it (44nm).

Partial Structural Functions of Molten CuBr Estimated from the Anomalous X-Ray Scattering Measurements

The individual partial structural functions of molten CuBr have been estimated from the anomalous X-ray scattering (AXS) measurements. This data processing includes the help of the reverse Monte Carlo (RMC) simulation technique. The cation-cation structure factor of a CuCu ( Q ) was found to be rather structureless and the closest Cu–Cu distance in molten CuBr was significantly smaller than that for Br–Br, indicating the like-ion penetration into the first unlike-ion coordination shell, similar to the molten CuCl case. It is then suggested that a disordered close packing of Br - ions where Cu + ions meander so as to take strongly disordered distribution by penetrating through the tetrahedral holes.

The genetic algorithm: refinement of X-ray reflectivity data from multilayers and thin films

Abstract A genetic algorithm (GA) technique has been implemented for determination of structural parameters of thin solid film and superlattice from the X-ray reflectivity and diffuse scattering data. The fundamental concepts underlying genetic algorithms are described along with examples of classical nanostructures illustrating successful application of GA. The method is demonstrated to be robust and flexible in comparison with conventional optimization techniques.

Grazing Incidence In-Plane X-Ray Diffraction Study on Oriented Copper Phthalocyanine Thin Films

Uniaxially aligned vacuum deposited films of copper phthalocyanine (CuPc) have been studied by means of angle-dispersive grazing-incidence X-ray diffraction. The lateral structure of the top surface of a 100-nm-thick film was successfully probed. It was revealed that the microcrystals near the surface have a finite in-plane distribution with a full-width at half maximum of 17.5°. In-plane diffraction profiles were transformed into a reciprocal space map that reproduced the electron diffraction pattern of a CuPc thin film reported previously.

Preparation and characterization of Yb:Y3Al5O12 fiber crystals

Abstract A micro-pulling-down process employing Ir crucibles and RF heating has been used to grow single crystal fibers of Yb-doped Y 3 Al 5 O 12 garnet (YAG). Single crystals ranging up to 550 mm in length have been produced. The fibers were about 1 mm in diameter and were seeded-grown in the direction. Results of X-ray rocking curve measurements and transmittance data were used to discuss the crystalline perfection of the fibers. The effective segregation coefficient of Yb 3+ in the process described is reported to be slightly less than 1.0 at a growth rate of about 5 mm/min.

Growth Process of Vacuum Deposited Copper Phthalocyanine Thin Films on Rubbing-Treated Substrates

Surface morphology, crystal lattice spacings and crystallite size of copper phthalocyanine (CuPc) thin films grown on rubbed surfaces were probed at different stages of growth, by means of atomic force microscopy (AFM) and X-ray diffraction (XRD). The films consisted of many slender crystallites extending along the rubbing direction, due to the α-type columnar structure along the same direction. AFM revealed that the aspect ratio of crystal domains increases as the films grow, implying a change in the ratio of crystal growth rates in the two different directions parallel to the substrates. XRD demonstrated marked differences in the two intercolumnar directions. The molecular spacing is expanded in the thickness direction at the initial stage of growth, while it remains constant throughout the growth in the lateral (c-axis) direction. The crystallite size in the thickness direction is always comparable to the film thickness, while the size in the c-axis direction shows no change.

A new x-ray metrology for determining cross-sectional profile of semiconductor device pattern

We have developed a new x-ray metrology for measuring surface periodic grating of semiconductor device pattern. X-rays irradiate surface of the device area with a shallow glancing angle, which is close to the critical angle of total external reflection of the surface material. The measured x-ray diffraction pattern is reflected to the average cross-sectional profile of the grating. The pattern made from SiO2 on Si with100 nm-pitch is analyzed by the present x-ray metrology. The obtained profile, for example, line width, height of the grating and so on are well agreed with that observed by cross-sectional transmission electron microscopy. The wavelength of x-ray that we use is 0.154093 nm and it is enough shorter than the critical length of the grating structure, even when the line width becomes 10 nm or less. Therefore, the resolution of the x-ray metrology will be maintained good enough for the analysis that will be required in the future. In addition, x-ray metrology can be measure the cross-sectional profile with nondestructively due to hightransmissivity of x-rays for the materials. Furthermore, the optical parameter of the materials for x-ray is well established, therefore, x-ray metrology is applicable for any materials of device patterns without uncertain empirical parameters.

Characterization of submicron-scale periodic grooves by grazing incidence ultra-small-angle X-ray scattering

A grazing incidence ultra-small-angle X-ray scattering measurement system using a laboratory X-ray source has been developed. Submicron-scale artificial periodic grooves on thermally oxidized silicon wafers are characterized using this system. They are fabricated by electron beam lithography. The average pitch widths of the grooves are determined accurately with a low standard uncertainty of less than 0.02%. The cross-sectional profiles are also analyzed by intensity ratios of higher-order diffraction peaks from the periodic structures and X-ray reflectivity measurements. The obtained cross-sectional profiles are in good agreement with those obtained by atomic force microscopy.

25 nm pitch comparison between a traceable x-ray diffractometer and a metrological atomic force microscope

A one-dimensional grating (1D grating) is one of the most important reference standards to calibrate nanometrological instruments, such as a critical dimension scanning electron microscope. Recently, the resolutions of nanometrological instruments have become higher, and 1D grating standards with smaller pitches are required. Based on this demand, 1D gratings with 25 nm pitch consisting of Si/SiO2 multilayer thin-film structures have been developed. Furthermore, pitch calibrations using metrological atomic force microscopes (metrological AFMs) and an x-ray diffractometer have been applied. In this study, the results of a 25 nm pitch comparison between a length-and-angle-standards-traceable x-ray diffractometer and a metrological AFM are reported.