Showing papers by "Kiyoshi Takamasu published in 2014"

Profile measurement of aspheric surfaces using scanning deflectometry and rotating autocollimator with wide measuring range

Abstract: High-accuracy aspherical mirrors and lenses with large dimensions are widely used in large telescopes and other industry fields. However, the measurement methods for large aspherical optical surfaces are not well established. Scanning deflectometry is used for measuring optical signals near flat surfaces with uncertainties on subnanometer scales. A critical issue regarding scanning deflectometry is that high-accuracy autocollimators (AC) have narrow angular measuring ranges and are not suitable for measuring surfaces with large slopes and angular changes. The goal of our study is to measure the profile of large aspherical optical surfaces with an accuracy of approximately 10 nm. We have proposed a new method to measure optical surfaces with large aspherical dimensions and large angular changes by using a scanning deflectometry method. A rotating AC was used to increase the allowable measuring range. Error analysis showed that the rotating AC reduces the accuracy of the measurements. In this study, we developed a new AC with complementary metal-oxide semiconductor (CMOS) as a light-receiving element (CMOS-type AC). The CMOS-type AC can measure wider ranges of angular changes, with a maximum range of 21 500 μrad (4500 arcsec) and a stability (standard deviation) of 0.1 μrad (0.02 arcsec). We conducted an experiment to verify the effectivity of the wide measuring range AC by the measurement of a spherical mirror with a curvature radius of 500 mm. Furthermore, we conducted an experiment to measure an aspherical optical surface (an off-axis parabolic mirror) and found an angular change of 0.07 rad (4 arcdegrees). The repeatability (average standard deviation) for ten measurements of the off-axis parabolic mirror was less than 4 nm.

Sidewall roughness and line profile measurement of photoresist and finFET features by cross-section STEM and TEM image for reference metrology

Abstract: The novel method of sub-nanometer uncertainty for the line width measurement and the line profile measurement using STEM (Scanning Transmission Electron Microscope) images is proposed to calibrate CD-SEM line width measurement and the standardization of line profile measurement as reference metrology. In accordance with the proposed method, we already have established the methodology of profile of Si line and photoresist feature for reference metrology. In this article, we applied the proposed method to the sidewall roughness measurement of photoresist features and line profile measurement of finFET features. Using the proposed method, specimens of photoresist feature and finFET feature are sliced as thin specimens of 100 nm thickness by FIB (Focused Ion Beam) micro sampling system. Then the cross-sectional images of the specimens are obtained by STEM and TEM. The sidewall roughness of photoresist features is estimated by the maximum slope of the image intensity graph at the edge. Then, the sidewall roughness is also measured by CD-AFM (Critical Dimension Atomic Force Microscope); we compared the results by STEM image and CD-AFM. Moreover, the line profile of finFET features is defined using TEM images for reference metrology. We compared the line width of fin measured by the proposed method and CD value by CD-SEM measurement.

Performance evaluation of a coordinate measuring machine’s axis using a high-frequency repetition mode of a mode-locked fiber laser

Abstract: We developed a multi-Fabry-Perot etalon (multi-FPE) for selecting high-frequency parts of repetition-frequency modes of a shortpulse mode-locked fiber laser at the wavelength of 1.55 mm. The 5-GHz repetition-modified laser beam is transmitted to a fiber-type Michelson interferometer. The interference fringes exhibit a temporal coherence pattern and can be used for measuring spatial positioning. The performance of CMM’s axis was determined directly from different positions of two interference fringes.

Two-color absolute length measuring method based on pulse repetition interval lengths

Abstract: A unique absolute length measurement method is proposed and demonstrated for the first time. Since it takes advantage of both the high-accuracy measurement capability of a pulse train interference method and the ability of a two-color method to compensate for environmental changes, the present method is expected to be useful for high-precision length measurement for not only the purposes of laboratory science but also for satisfying the requirements of industry. A length measurement was performed to demonstrate the feasibility of the proposed method.

Fabrication and Composition Control of Three-Dimensional Dielectric Metal Microstructure Using Photocatalyst Nanoparticles

Abstract: Recently, three-dimensional microstructures have been attracting much attention because of their potential application to electromagnetic devices operating with specific frequencies such as THz wave. For suitability in such applications, the structures often need to have complex three-dimensional shapes, be smaller than or at least as small as the applied wavelengths, consist of metals or dielectric materials, and have certain electromagnetic characteristics such as high permittivity. Although there are several methods for fabricating micro-structures, few of them satisfy all of these conditions. We propose a new fabrication method for dielectric-metal three-dimensional structures with sizes of a few tens of micrometers. The main feature of our method is the extraction of metal using photocatalyst nanoparticles. Silver ions in solution are reduced to neutral silver by electrons from the photocatalyst nanoparticles. Experimental results show that our system can be used to fabricate threedimensional structures, and we propose a new method for controlling the composition of the structures.

Lateral resolution improvement of laser-scanning imaging for nano defects detection

Abstract: Abstract Demand for higher efficiency in the semiconductor manufacturing industry is continually increasing. In particular, nano defects measurement on patterned or bare Si semiconductor wafer surfaces is an important quality control factor for realizing high productivity and reliability of semiconductor device fabrication. Optical methods and electron beam methods are conventionally used for the inspection of semiconductor wafers. Because they are nondestructive and suitable for high-throughput inspection, optical methods are preferable to electron beam methods such as scanning electron microscopy, transmission electron microscopy, and so on. However, optical methods generally have an essential disadvantage about lateral spatial resolution than electron beam methods, because of the diffraction limit depending on the optical wavelength. In this research, we aim to develop a novel laser-scanning imaging method that can be applied to nano-/micro manufacturing processes such as semiconductor wafer surface inspection to allow lateral spatial super-resolution imaging with resolution beyond the diffraction limit. In our proposed method, instead of detecting the light intensity value from the beam spot on the inspection surface, the light intensity distribution, which is formed with infinity corrected optical system, coming from the beam spot on the inspection surface is detected. In addition, nano scale shifts in the beam spot are applied for laser spot scanning using a conventional laser-scanning method in which the spots are shifted at about a 100 nm pitch. By detecting multiple light intensity distributions due to the nano scale shifts, a super-resolution image reconstruction with resolution beyond the diffraction limit can be expected. In order to verify the feasibility of the proposed method, several numerical simulations were carried out.

High-Accuracy Calibration of CMM Using Temporal-Coherence Fiber Interferometer with Fast-Repetition Comb Laser

Abstract: A coordinate measuring machine (CMM) is a measuring system with the means to move probing system and capability to determine spatial coordinates on working surface. CMM is used in many industry fields from few micrometers of work pieces to a 5-meter truck. The verification method of CMM is done following international standard. The artifacts for calibrated reference length are the end standards, such as gauge block and step gauge, or laser interferometer for large size CMM. The current laser interferometer is operated by continuous laser and interference fringe counting. One constraint of continuous laser is an incremental measurement. The measurement path cannot be interrupted during the measurement period. We developed a new absolute interferometer system from a short-pulse mode-locked fiber laser. A Fabry–Perot etalon (FPE) is used to select high-frequency parts of repetition-frequency modes of the mode-locked comb laser at the wavelength of 1.55 μm. The 5-GHz repetition-modified laser beam, which is realized by a new fiber-type FPE, is transmitted to a fiber-type Michelson interferometer. The interference fringes exhibit a temporal coherence interference and can be used for measuring spatial positioning. The temporal coherence between different pairs of modified pulse trains is referred to as absolute length standards. The performance of CMM was determined directly from different positions of two interference fringe patterns.

Distance Measurement Using Temporal-Coherence Interferometer with Optical Frequency Comb and Fiber Etalons

Abstract: Absolute distance measuring method is developed by using temporal-coherence interferometry of optical frequency comb with 15-GHz fiber etalons, and a scanning stage. The fringe processing is automatically made with electric circuit.

Microscopic observation device

Abstract: A microscopic observation device (20) includes: an optical system comprising a point light source (30), an illumination lens (32), a beam splitter (34), an objective lens (36), and an imaging lens (38); a detection system comprising a light distribution detector (40); a sample stage (50) capable of moving an observation sample (10) in nano-order; and a computer (60) into which a resolving program for resolving the observation sample (10) is installed The location (observation point) on the observation sample (10) to be illuminated by the spot illumination from the point light source (30) is shifted by a predetermined shift amount equal to or less than 100 nm, and the intensity distribution (light distribution) of the observation light from the observation point is detected for each shift Then, the resolving program is executed so that the light distributions detected for each shift are subjected to an inverse problem analysis, from which an approximated sample is obtained as a solution As a result, it is possible to resolve objects that are apart by a distance of equal to or less than 100 nm

Length Traceability Using Optical Frequency Comb

Abstract: High-precision length measurements are strongly demanded for not only industry requirements and science purposes.In 2009, a femtosecond optical frequency comb (FOFC) was adopted in Japan as the national standard tool for measuring length. Recently, numerous studies have focused on FOFC-based high-precision length measurement because this approach offers the possibility of development of a ultimate green length traceability system. A single-wavelength helium–neon (He–Ne) laser was used as a length standard. An FOFC emits discrete pulse-train-shaped light. This markedly different characteristic exists between a He-Ne laser and an FOFC is the reason for the challenge. Previous attempts to challenge this problem have not been satisfactory. This has limited the development and applications of FOFC-based length measurement. In this work, we review our efforts of FOFC-based high-precision length measurement toward developing an ultimate green length traceability system.