Papers by Author: Jun Shimizu

Abstract: This study aims to develop a cutting method, which enables to generate a localized hydrostatic pressure field in the vicinity of cutting zone in order to improve the machined surface integrity without causing unnecessary plastic deformation. In the previous work, a molecular dynamics simulation was performed using a newly developed cutting tool equipped with a planer jig with a rectangular hole for the cutting chip elimination, and it was confirmed that the developed cutting tool has advantages in giving a relatively high-hydrostatic stress field in the vicinity of the cutting zone and in suppressing the burr formation. In this report, further molecular dynamics simulation was performed in order to clarify the influence of jig shape on the cutting phenomena and machined surface integrity. As a result, it is found that a cutting tool of which front and side except for the rectangular hole are covered by the planer jig is the most advantageous for supplying high hydrostatic pressure and suppressing burr formation.

Abstract: Finishing process of sapphire wafer is meeting huge challenge to fulfill the strict requirement of high surface quality in semiconductor industry. Fixed abrasive process, although can guarantee the profile accuracy, leaves damaged layer on the surface or subsurface of sapphire wafer. Chemical mechanical polishing (CMP) is famous for providing great surface roughness, however, sacrifices surface geometrical accuracy. Therefore, a new chromium oxide (Cr₂O₃) sapphire grinding wheel based on chemical mechanical grinding (CMG) principle has been developed and its performance has also been put into examination. The experiment result has demonstrated that Cr₂O₃ possesses an outstanding potential in terms of a high material removal rate of sapphire wafer, meanwhile, largely reduces surface roughness from about 150nm to below 10nm in 1 hour. In addition, the design of experiment (DOE) has also been carried out to study the effect of influencing factors towards ultimate surface roughness of sapphire wafer. It reveals that the revolution speed of sapphire wafer bears twice greater influence towards surface roughness than the revolution speed of grinding wheel.

Abstract: Applicability of a generic optical spectrum analyzer that is familiar with laser experiments is investigated for on-site wafer thickness measurements in the thinning process, to resolve the issues regarding mismatch in the thickness range of previous thickness measurement system. The optimizations in terms of the spectral range, the spectral resolution and the dynamic range are successfully conducted by use of the optical spectrum analyzer. Owing to both high spectral resolution and wide dynamic range in near infrared spectral measurements, full range thickness measurements for the initial thickness 775μm and the terminal thickness 1μm and nanometer order accuracy are implemented.

Abstract: The phenomenon that bubbles or particles are suspended at the node position of a standing wave of sound is known as acoustic levitation and has recently been applied in the fields of semiconductors, aerospace, and biology [1-3]. By using this phenomenon in this study, a new classification method has been proposed, and a device has been developed to sort objects in accordance with their densities. Unlike the conventional methods as such as centrifugal particle separation or magnetic separation, this method can separate fine particles both of metal and non-metal and without contact easily only using acoustic power. First, we derived the acoustic radiation pressure to be applied to the object from King’s theory, and then we designed and developed a twin-transducer system to apply the required levitation force. The distributions of sound pressure and particle velocity were then visualized. Finally, a series of experiments was conducted to show the capability of classifying the fine abrasive SiO₂ particles and fine iron particles (φ = 50 μm).

Abstract: The wafer grinding by use of fixed abrasive diamond wheels is required to create a high-quality wafer surface in a short time. In general, it is known that the grinding performance of diamond wheel is mainly dependent on grinding wheel specifications and grinding conditions. The cutting edge distribution or abrasive protrusion height in depth-wise of a specified wheel is one of the most important factors to determine the finishing surface roughness and the grinding force, which in turn determine the surface and subsurface quality of ground wafers. The overall purpose of this study is to understand the dynamic behavior of each diamond abrasive via modeling an actual diamond wheel and simulating of wafer grinding. In previous report [1], we have theoretically analyzed three-dimensional cutting edge distribution on the working surface of diamond wheels. This paper reports our recent achievements in the evaluation of 3-D cutting edge distribution in depth-wise of a specified wheel via the bearing ratio of its topography.

Abstract: Wafer thickness meter by reflection spectroscopy is used for on-site thickness inspections in wafer thinning process, because of its excellent properties as high measurement accuracy in very thin wafers inspections by non-contact sensing. In practice, ground surfaces are not ideal flat surfaces. Thus the spectra suffers influences of the surface roughness and the waviness, as modifying spectral features by optical diffusion, and as decreasing the reflection received by dispersion of propagating directivity. In this paper, we investigate how the surface integrities of ground wafer surfaces are involved in the thickness measurements by both theoretical and experimental approach, to investigate the requirements in sample conditions and to guarantee the accuracy of the measurements.

Abstract: 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.

Abstract: As a typical multi-functional single crystal material, Lithium tantalate (LiTaO₃ or LT) exhibits its excellent electro-optical, pyroelectric and piezoelectric properties, and has now been widely applied into many applications, especially in the telecommunication field. However, the most critical issue in the process is its pyroelectric effect and piezoelectric effect which potentially leads to crack initiation during grinding. Because it is rich in plasticity, LT demands larger specific energy for material removal. As the most machining energy is eventually converted into heat, LT undergoes a rapid rise in temperature during the grinding process, thus highly risks in thermal shock. In order to clarify the thermal influence on the grinding process of LiTaO_3, the effects of coolant temperature, diamond grinding wheel geometry and material of substrate are investigated in this research. The experimental results show that the increasing rate of grinding torque (or force) and surface roughness are two major factors dominating the crack initiation during grinding of LT wafers. Via a DOE (design of experiment) analysis, coolant temperature and wheel type stand out as the main factors influencing on the increasing rate and wafer surface roughness.

Abstract: 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.

Abstract: 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.