Hirotaka Ojima

Design of Digital Filters for Si Wafer Surface Profile Measurement – Noise Reduction by Lifting Scheme Wavelet Transform

Recently in semiconductor industry, production of ever flatter, thinner and larger silicon wafers are required to fulfill the demands of high-density packaging and cost reduction. In geometric evaluation of Si wafers, according to SEMI (Semiconductor Equipment and Materials International) standards, the required wafer flatness approaches to the 22 nanometers by year 2016 [1]. For such application, uncertainty of measured data is encountered as a severe problem because the requirement has met the limit of available instrument in terms of resolution and reliability. In order to precisely evaluate the wafer profile, it is essential to remove the noise from the measured data. Described in this paper is design and development of digital filters for denoising. In previous paper, digital filters for denoising with Haar wavelet transform are described. In this paper, the new filters by use of 2nd generation wavelet transform (lifting scheme) are proposed and show better performance of decomposition in the spatial frequency domain and amplitude domain.

Study on Grinding Processing of Sapphire Wafer

This paper reports our recent results on the diamond grinding process of single crystallized sapphire wafers. It was found that the diamond grains were severely dislodged at the wheel/ workpiece interface and the material was removed by a mixed process of both grinding and lapping. Grinding governed the wafer center while lapping dominated its fringe. By increasing the wheel speed, it was able to shift the dominant process from lapping to grinding, and achieve a better surface roughness. Nine diamond wheels varying in both concentration and bond material were tested in surface grinding of 6 inch sapphire wafer, to investigate the dynamic behavior of diamond grain in the grinding process and its resultant surface quality and productivity.

Path Control Scheme for Vision Guided Micro Manipulation System

Cloning is new and growing industry. However, the cell manipulation like enucleating and injection are manually done by skilled operators with the aid of a microscope, and thus tedious and time consuming. Thus, the objective of this research is to develop a manipulation system which is capable to automatically implement necessary operations, with high accuracy, reliability and repeatability, on the multiple targeted cells. In this paper, the path control scheme developed for vision guided micro manipulation system is proposed.

Fabrication of Surface Microtexture by Vibration Assisted Cutting

mproving materials surface function by introducing nano/micro surface textures is of great interest in various fields. The authors have also achieved an improvement in the photocatalytic surface function by introducing the microcutting grooves texture on the titanium dioxide surfaces. In this report, the authors performed the vibration assisted cutting to fabricate finer surface microtextures anticipating future usage as microtexture moulds for the nanoimprinting and/or injection moulding. In the experiment, a pure copper plate was cut using a sharply pointed triangular diamond tip vibrated by a fast tool servo system in the direction of cutting depth with μm order amplitude and kHz order frequency. As a result, it was found that the periodical micro concave-convex patterns with the combinations of impressions and pileups can be obtained by the proposed method using almost the same vibration amplitude as the cutting depth. It was also achieved that a micro-textured surface with numerous concave-convex patterns less than 1 μm in height with 3 μm in pitch.

Enhancement of Photocatalytic Reaction of Titanium Dioxide Film by Surface Texturing

This study aims to study the influence of surface topography on the photocatalytic reaction of TiO2 film surfaces. In this work, a textured TiO2 film surface was fabricated by anodic oxidizing a titanium plate with micro grooves, and its wettabilty was evaluated. Micro grooves were machined on a 3-axis NC control precision machine tool using a single point diamond cutter with a tip radius of several hundred nanometers. Anodic oxidation experiments were conducted by using the self-developed equipment with diluted acetic acid as the electrolyte. It was found that the wettability of the TiO2 film surface textured by microcutting was superior to that textured by polishing under the irradiation environment of ultraviolet rays. The wettability of photocatalytic film surfaces could be improved by increasing the surface area.

Wave-based Analysis and Wave Control of Ladder Networks

This paper investigates the wave-based analysis and the wave control for ladder electric networks. The results are a generalized version of our previous work for the cascade connected damped mass-spring systems. We first clarify the class of the ladder networks which satisfies the three condition for the propagation constants to be analyzed by the wave-based analysis. Secondly, for the class of the networks, we investigate the analyticity of the secondary constants and positive real property of the characteristic impedances. Properties of the impedance matching are also investigated. A numerical example for a mechanical system shows effectiveness of the impedance matching for vibration control.

Influence of Surface Micro Texture on Photocatalitic Function of Titanium Dioxide Film

This study aims to develop a high-functional photocatalytic film, of which surface is regularly textured by the micro machining technique in order to earn the real surface area. In this work, a regularly textured TiO2 film surface was fabricated by anodic oxidizing a pure titanium plate with regularly arrayed micro cutting grooves, and its wettabilty was evaluated. Micro cutting grooves were machined by a 3-axis NC control precision machine tool with a single point diamond cutter. Anodic oxidation experiments were conducted by using the self-developed equipment with diluted acetic acid as the electrolyte. As a result, it was found that the wettability of the TiO2 film surface regularly textured by synchronized 3-axial micro cutting was superior to those of the mirror finished or irregularly textured surfaces under the irradiation environment by the ultraviolet rays.

Visual Feedback Control of a Micro Lathe

Micromachining progresses rapidly in recent years. In this research, a micro lathe which is installable and operational inside SEM vacuum chamber has been designed and developed. As a first step, visually guided micro lathe system is developed with image of CCD camera device instead of SEM image. Unlike the conventional feedback control which positions the X-Y table only, this scheme offers a direct control of the position, path and speed of the tool tip. Using proposed method, cutting experiment was achieved, and it is confirmed that developed micro lathe system is effective to do cutting.

Development of Microtextured Photocatalytic Surface by Vibration-Assisted Scratching

It is known that the TiO2 has some photocatalytic functions, even though they are relatively weak and their further enhancements are necessary for wider practical usages. On the other hand, improving materials surface functions by introducing microtextures is of great interest in various fields. Under such circumstances, the present study is aiming at developing a high-functional photocatalytic surface by earning the real surface area and reducing the light reflection and so on with the support of microtexturing technique. In this work, a pure Ti plate surface, which was covered with numerous micro impressions and micro pile-ups formed by the vibration-assisted microscratching, was anodized in order to obtain a regularly microtextured TiO2 film on the uppermost surface of Ti plate, and its wettabilty was evaluated in order to investigate its potential as the photocatalyst. As a result, it was found that the wettability of the TiO2 film surface regularly microtextured by the vibration-assisted microscratching was superior to those of the mirror finished one under the irradiation environment by the ultraviolet rays.

A Thin Silicon Wafer Thickness Measurement System by Optical Reflectmetry Scheme Using Fourier Transform Near-Infrared Spectrometer

In this study, measurable thickness range was improved by re-customized components of the thickness measurement system using the method of Fabry-Perot interference signature analyzing. A Fourier transform near infrared (FT-NIR) spectrometer with indium gallium arsenide was used in the developed system. As a result of the sensitiveness in the whole near infrared band and high spectral resolution united with high signal noise ratio of the FT-NIR spectrometer, the maximum measurable thickness is improved to 88μm while sub-micron order of the minimum measurable thickness is also improved.