Quantum Measurement and Instrumentation Laboratory (Ogi Laboratory)

Professor Hirotsugu Ogi
Associate Professor Motohiro Nakano
Assistant Professor Yasushi Oshikane

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“Nano-world” observed by “light”

The Quantum Measurement and Instrumentation Laboratory conducts research into the nature of “light”. Because the emission and detection of light both involve an interaction with electrons, this is a research field that measures quanta. Although it used to be considered impossible to view the nanometer world with light because this was smaller than the diffraction limit of optical lenses, the advent of the Scanning Near-field Optical Microscope (SNOM) has demolished this basic assumption. Our laboratory constantly meets the challenges of applying “light” to the state-of-the-art science and technology for manufacture with the following projects: (1) development of a SNOM with the world’s best spatial resolution of vertical 2 nm and lateral 10 nm, (2) development of a PDI that measures the absolute surface figure of mirrors at a nanometer level accuracy, (3) development of light scattering method that can detect nanometer size defects on large-diameter semiconductor substrates, and (4) development of a laser-plasma light source to produce extreme ultraviolet rays (EUV) for next-generation LSI lithography system. At our laboratory, we enjoy viewing and considering the nano-world where light and electrons interact with each other, and conducting research that pave the way to the future of nano-technologies.

Development of Scanning Near-field Optical Microscope (SNOM)

As seen in the conceptual diagram in Figure 1(b), when there is a total reflection of light on an internal surface of glass, light seeps out of the glass substrate only for a short distance. When this evanescent light illuminates a microscopic plastic ball, a strong near field of light is generated below the plastic ball with about 10 nm thickness. If the surface of a sample is placed within this near field, the change in the intensity of scattered light highly depends on the distance between the ball and the sample. When this probe is scanned over the surface of the sample and the intensity of the scattered light is measured, the shape of the surface of the sample can be measured with a spatial resolution exceeding the diffraction limit of light.
As shown in Figure 1(a) our laboratory has developed SNOM system with a nanometer level resolution, which is demonstrated in the micrograph of the microscopic holes (20 nm depth and 100 nm diameter) in Figure 1(c). Furthermore, we are making effort to establish a new academic field of near-field optics, which aims to understand the interactions between light and electrons using electromagnetism.

Development of Point Diffraction Interferometer (PDI) with spherical wavefronts from optical fibers

Figure 2 shows the result of a measurement on a 200 mm diameter concave mirror surface with nanometer accuracy using light from the tip of an optical fiber. Light coming from the tip of a optical fiber propagates as a diffracted spherical wave, which can be considered as a perfect sphere. Measurements on a spherical mirror to determine the accuracy of the finished sphere at a sub-nanometer scale is possible using a Point Diffraction Interferometer (PDI) with this spherical light wave as reference wavefronts. With this high precision PDI, it is also plausible to measure and evaluate the most advanced mirrors used in synchrotron facilities and gravitational wave detectors.

Development of nanometer size defects detection apparatus using light scattering method

Light scattering method is an excellent procedure that allows us to view extreme wide area, which is 10,000,000 times larger than that of an STM or a transmission electron microscope, with nano-structures on a sample surface. Challenging the limits of the optical scattering method, our laboratory has developed equipment that can quickly detect surface defects at a nanometer scale with ultra high sensitivity without contacting the sample. This apparatus uses a short wavelength, high intensity argon ion laser, which illuminates a wafer surface, to image microscopic defects by detecting extremely weak scattered light from defects using a high sensitive cooled CCD camera. Figure 3(a) shows a white line within a 0.6 mm square image, which is a groove shaped nanometer size defect called a scratch with a width and depth of about 2 nm each recorded by an optical configuration as shown in Figure 3(b). The next generation of ultra LSI manufacturing requires measurement equipment capable of detecting surface defects on silicon wafers with high precision. The optical scattering method is receiving much attention for this application.


(b) ↑ Zoom
<Figure 3>
(a) Observation of ~2 nm width scratches on a silicon wafer using a CCD camera, and
(b) an optical configuration for this measurement

Development of laser plasma EUV light source

When high energy is suddenly injected into a target material by focused short-pulse laser irradiation, the material goes beyond three states of matter (solid, liquid, and gas), and enters into the “fourth state” of “plasma”. Light from stars, lightening as an atmospheric discharge, the polar aurora, and the glow discharge inside a fluorescent lump are all luminescent phenomena from plasma. Plasma excited by laser emits light as electromagnetic radiation of various wavelengths, ranging from X-rays (<1 nm wavelength) to infrared rays (>1 µm wavelength). The next generation lithography (NGL) for 45 nm production of semiconductor integrated circuits requires an extreme ultraviolet (EUV) light source with a central wavelength of 13.5 nm. Our laboratory is developing a clean and high intensity EUV light source for NGL Figure 4 illustrates schematic of generating EUV emission from laser produced tin plasma inside a through hole. When the laser is irradiated into the through hole, the following process is expected. (a) Laser ablation is generated from the wall surface of the through hole. (b) This cylindrical plasma is excited by focused laser and emits strong EUV because the intensity is superposed along the axis of the hole.

<Figure 4>
(a) Generation of laser plasma in a through hole, and (b) EUV emission from tin plasma

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2-1 Yamada-Oka, Suita, Osaka
565-0871, Japan
Department of Precision Science & Technology, Osaka University

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