Yoshihiro Tezuka

Theoretical and experimental studies on the electronic structure of M2O3 (M = Ti, V, Cr, Mn, Fe) compounds by systematic analysis of high-energy spectroscopy

Abstract A systematic investigation of 2p core-level X-ray photoemission spectra (2pXPS) of a series of transition metal (TM) sesquioxides M 2 O 3 (M = Ti, V, Cr, Mn, Fe) is reported. Theoretical analysis was carried out by means of an MO 6 cluster model with the full multiplet structure of the M ion and the calculated results of the 2pXPS are in good agreement with the experimental data. Moreover, theoretical and experimental investigations of 3pXPS, 3sXPS, valence XPS and bremsstrahlung isochromat spectra (BIS) of Cr 2 O 3 were also performed and all of these experimental data are satisfactorily reproduced with the cluster model approach. The character of the insulating energy gap of these M 2 O 3 compounds was also studied based on the spectral analysis. It is shown that the M 2 O 3 compounds from Ti 2 O 3 to Mn 2 O 3 are classified as intermediate-type insulators between charge transfer (CT) and Mott-Hubbard (MH) insulators, and Fe 2 O 3 is classified as a CT insulator.

Soft x‐ray emission spectrometer for undulator radiation

An experimental system for high‐resolution soft x‐ray emission spectroscopy was made. The experimental system is designed to be attached to the undulator beamlines. Spectrometer uses the Rowland circle geometry in which input slit, spherical grating, and multichannel detector lie on the focal circle. Three blazed holographic gratings are changeable in the vacuum. The Rowland circle radii of gratings are 5, 7, and 10 m and their line densities are 600, 1200, and 2400 lines/mm, respectively. The available photon energy is from 30 to 1200 eV. The resolution ΔE is achieved to 0.06 eV by 50 μ‐input‐slit width for hν=120 eV. Several experimental results measured by this system are presented.

Actinic inspection of extreme ultraviolet programed multilayer defects and cross-comparison measurements

The production of defect-free mask blanks remains a key challenge for extreme ultraviolet (EUV) lithography. Integral to this effort is the development and characterization of mask inspection tools that are sensitive enough to detect critical defects with high confidence. Using a single programed-defect mask with a range of buried bump-type defects, the authors report a comparison of measurements made in four different mask inspection tools: one commercial tool using 488nm wavelength illumination, one prototype tool that uses 266nm illumination, and two noncommercial EUV “actinic” inspection tools. The EUV tools include a dark field imaging microscope and a scanning microscope. Their measurements show improving sensitivity with the shorter wavelength non-EUV tool, down to 33nm spherical-equivalent-volume diameter, for defects of this type. Measurements conditions were unique to each tool, with the EUV tools operating at a much slower inspection rate. Several defects observed with EUV inspection were below...

Simultaneous angle-resolved measurement of the band structure of single-crystal graphite by an improved two-dimensional display analyzer

We have embodied a new version of two‐dimensional display‐type spherical mirror analyzer [H. Daimon and S. Ino, Rev. Sci. Instrum. 61, 57(1990)]. A couple of concentric hemispherical small grids and 12 pairs of obstacle rings have been attached to the original type of analyzer in order to operate with a constant pass‐energy mode and improve the uniformity of the energy resolution of the analyzer all over the detection area, respectively. We performed a test on the resolution of the analyzer, and applied it to the simultaneous angle‐resolved photoelectron spectroscopy on the band structures of single‐crystal graphite (Kish graphite) within the acceptance cone of ±50°. The observed band structure is in good agreement with those reported by other investigators. We observed a ring‐like pattern which enlarged as the binding energy approached the Fermi level. This ring is ascribed to the cross section of the π band. Although the designed energy resolution is 1% of the pass energy, the minimum value realized rea...

High-speed actinic EUV mask blank inspection with dark-field imaging

We proposed an actinic (at-wavelength) EUV mask blank inspection method providing a printable phase-defect detection capability within the whole area of the mask blanks in an allowable inspection time. The inspection tool based on our method consists of optics for illuminating a mask blank with an EUV light, a mask blank stage, Schwarzschild optics for dark-field imaging, and a CCD camera. Phase-defect detection experiments were performed using a 10 Hz LPP source and with 0.2 NA imaging optics with the center obscuration NA of 0.1. Two-dimensional dark field image signal of 0.5 mmX0.5 mm area was captured by the CCD camera with 1M pixels and the phase-defects with the size down to 70 nm were successfully detected. In addition, a programmed phase defect and natural defect with 2 nm height were clearly detected. Inspection time including image capture and data processing for 0.5 mmX0.5 mm area was approximately 2 second. This is equivalent to an inspection time of 800 seconds/cm2. Inspection speed will increase by more than 10 times when combined with high power light source and high speed data acquisition. Although further optimization is needed, possibility of actinic inspection of EUV mask blanks within a practical inspection time has been demonstrated.

Sensitivity-Limiting Factors of at-Wavelength Extreme Ultraviolet Lithography Mask Blank Inspection

Sensitivity-limiting factors of at-wavelength inspection for extreme UV lithography (EUVL) mask blanks have been analyzed. The sensitivity of the inspection tool is modeled on the basis of the inspection image of programmed multilayer defects and the characterized attributes of the tool components. The characterization includes point spread function (PSF) analysis of the imaging optics and the back-illuminated charge-coupled-device (BI-CCD) sensor as well as power spectral density (PSD) analysis of the mask blank surface. The statistical scaling of signal-to-noise ratio (SNR) in conjunction with the variables of optics, sensors, and mask blanks has predicted effective improvement paths of its sensitivity. Increasing the magnification of optics, reducing the total PSF, and improving the roughness of mask blanks will address the needs for its application in future generations. Signal intensity dependency on the geometrical attributes of defects is also studied by both experiment and electromagnetic simulation. It is revealed that the bottom height of defects and defect smoothing throughout the multilayer deposition significantly influence defect signal intensity. Comprehensive measures to accommodate a variety of defects and to mitigate associated risks are also discussed.

Actinic detection and signal characterization of multilayer defects on EUV mask blanks

Actinic (at-wavelength) inspection of EUV mask blanks using a dark-field imaging proved a high sensitivity for detecting multilayer defects through detecting programmed phase defects accurate to 70nm in width and 2nm in height without any detection of false defects. Characterization of the experimental actinic inspection tool is ongoing to find the ultimate sensitivity of this tool to define the detailed specification of a proto-type tool. In this paper, we present a detailed analysis of the defect signal intensity compared with AFM measurements taken from more than 20 programmed phase defects. This analysis proved that the signal intensity is mainly correlated with the volume of bumps whose sizes range from 2.8nm to 6.0nm in height and from 59nm to 86nm in width. The correlation suggests that the intensity variation within the group of the same design size reflects the actual variation of the defect size. Some natural defects other than programmed defects are also detected. The comparison of the defect signal and AFM analysis suggests that one of the detected defects is not a pure phase defect but more like an amplitude defect. The smallest natural defect had a surface height as low as 1.5nm, which can only be detected by lowering the detection threshold to the level with some statistically expected false defect counts. Current efforts to improve its detection capability while minimizing false defect detection are also discussed.

Actinic detection of multilayer defects on EUV mask blanks using LPP light source and dark-field imaging

The development of defect-free mask blanks including inspection is one of the big challenges for the implementation of extreme ultraviolet lithography (EUVL), especially when the introduction of EUVL is rescheduled to a later technology node. Among others, inspection of multilayer coated mask blanks with no oversight of critical defects and with minimal detection of false defects is a challenging issue for providing mask blanks free of defects or with thorough characterization of any existing defects. MIRAI Project has been developing a novel actinic (at-wavelength) inspection tool for detecting critical multilayer defects using a dark-field imaging and a laser-produced plasma (LPP) light source, expecting better sensitivity and better correlation with printability. The first experimental set up is completed for proof-of-concept (POC) demonstration using 20x Schwarzschild imaging optics and a backsideilluminated CCD. An in-house LPP light source is integrated to optimally illuminate the area of interest by EUV with a wavelength of 13.5nm. For its illuminator, a multilayer-coated elliptical mirror is used to illuminate a mask blank with the EUV that is collected within a wide solid angle from the light source. The first EUV dark-field image is obtained from a mask blank with programmed multilayer defects which are manufactured by locating well-defined patterns before depositing Mo/Si multilayer on EUV mask substrate. All the fabricated multilayer defects down to 70nm in width and 3.5nm in height are detected as clear signals that are distinguishable from the background intensity arising from the scattering by the surface roughness of the multilayer-coated mask blank. We have also detected a phase defect as low as 2nm in height. False defect count was not only zero within the area of view but also statistically confirmed to be less than one within the whole area of a mask blank assuming the extrapolation of observed fluctuation of background intensity is applicable. EUV pulse energy measurements and a CCD speed scaling suggested that the inspection throughput of 2 hours per mask blank will be feasible. The actinic tool based on this scheme will, not only serve for benchmarking with non-actinic tools or support multilayer deposition process improvements, but also be a viable choice for qualification of premium EUV mask blanks.

Surface electronic structure of ordered alkali- and noble metal-overlayers on Si(111)

Abstract Some progresses of our photoemission studies for ordered metal/Si(111) surfaces are reviewed. The 5-6-7 model having π-bonded chain structure on the alkali metal (AM) induced Si(111)3 × 1 surfaces is strongly suggested from the comparison between our results of angle resolved photoelectron spectroscopy (ARPES) and recently reported theoretical calculations. We also focus on the difference of the Si 2p surface core level shifts (SCLS) between Ag induced- and AM induced-Si(111)3 × 1 surfaces. Finally, we discuss the electronic and geometric structures of the Si(111)5 × 2, α- 3 × 3 , β- 3 × 3 and 6 × 6-Au surfaces from our ARPES and SCLS studies.

Concept of ultra-fast at-wavelength inspection of defects on a multilayer mask using a laser-produced plasma source

New configuration is presented for ultra-fast at-wavelength inspection of defects on multilayer mask blanks. Key ideas are detecting defects in a high NA dark-field observation by using a Schwarzschild objective, sub-micron resolution 2D imaging of mask surface on a detector, and large etendue illumination by using a laser-plasma source. Expected time for inspecting a whole mask is shorter than 2 hours.