Papers by Author: Hiroshi Eda

Abstract: A method to easily and economically manufacture more precise patterns compared with usual MEMS technique has been searched for. Under such circumstances, this research aims to clarify the formation of nano-scale protrusion structure produced by local anodic oxidation on Si wafer surface in expectation of the nano/micro mold production for nanoimprint lithography in future. In this report, the influences of contact width and distance between probe tip and Si wafer surface (distance between terminals) on the size and shape of protrusion patterns were examined in order to clarify the fundamental phenomena in local anodic oxidation. A scanning probe microscope equipped with a current measuring unit was utilized in local anodic oxidation experiments. As a result, it was confirmed that the size of generated protrusion structure became larger with increasing the contact width and became smaller with increasing the distance between probe tip and Si wafer surface. These facts will be useful in producing 3-D nanostructures in future.

Abstract: TiO2 has some unique photocatalytic functions and some of them have been utilized industrially, and further functional enhancement and performance enhancement of TiO2 have been required. Under such circumstances, this study aims to clarify the influence of surface topography on the photocatalytic reaction of TiO2 film surface. As the first step, the optimum mixing ratio in film preparation by using TiO2 powder was examined and the films with several kinds of surface roughnesses were prepared. And, the influence of surface topography on the wettabilty, which is one of the photocatalytic functions of TiO2 was evaluated. As a result, it was confirmed that the wettability of TiO2 films could be improved by increasing both the surface roughness and actual surface area under the ultraviolet rays irradiation environment.

Abstract: Silicon wafer thinning process is meeting great challenges to fulfill requirements of ultra-thin IGBT for automotive applications. Chemo-mechanical grinding (CMG) process is potentially emerging stress relief thinning process which combines the advantages of fixed abrasive machining and chemical mechanical polishing (CMP). A major issue in CMG of Si wafers is the relatively low material removal rate (MRR). This paper studies the influence of the wheel specifications and grinding conditions on the MRR of CMG. Two sets of three-factor two-level full factorial designs of experiment (DOE)[1] are employed to reveal the main effects and interacted effects of CMG wheel specifications and grinding parameters on MRR. The optimal combination scenarios for improving MRR of CMG are analysized and obtained. By use of the optimal CMG wheel and grinding parameters, the MRR of more than 60nm/min is achieved.

Abstract: Currently, most of the diamond turning tools used for precision machining are still manually manufactured, the profile accuracy of the diamond cutting edge depends on the operator’s experience and skill, so that the process need to be automated. Therefore in this research, an automated grinding system has been developed for the diamond turning tools, controlled by a vision system. The profile of the diamond turning tools is captured in real time via CCD camera. The deviation from an ideal circle is calculated and feedback to the controller, the grinding system then removes cutting edge of turning tool selectively to achieve high quality and high productivity.

Abstract: This study aims to clarify the interaction between Si wafer and individual diamond abrasives in grinding at nanometer level and to estimate the grinding conditions for minimizing the surface defect. This paper reports on the results obtained through nano-scratching experiments in vacuum by an atomic force microscope (AFM) and simulations by using the molecular dynamics method by applying Tersoff potential for Si-Si atomic interaction under room and high temperature, respectively, to examine the influence of the grinding heat on the materials removal process. As a result, it was proven that the scratch groove under high temperature becomes deeper than that under room temperature from the experiments, and it was also observed that the formation of the amorphous phase around the scratch groove under high temperature becomes a little bit larger than that under room temperature from the simulations.

Abstract: In this paper, the surface and subsurface of silicon wafers ground by different wheels have been studied. In the conventional grinding with diamond wheels, it is shown from the top that the subsurface of wafer consists of amorphous Si, followed by a thin damaged layer, strained crystal with a large compressive residue stress, and then the bulk material in single crystal. In a severe condition which causes grinding burn, part of amorphous Si is re-crystallized to form a poly-crystal Si, and part of amorphous Si possibly reacts with oxygen to form SiO2. This phenomenon becomes more pronounced in the backgrinding process with a fine grit diamond wheel when the conditions are improperly selected. In order to obtain a defect-free crystal Si structure in grinding, authors have proposed a new chemo-mechanical grinding (CMG) process which enables to remove Si from wafer but with no structure transformation induced to its surface.

Abstract: The single crystal of Si is still one of the most important candidates among other materials including Single crystals of SiC, GaN, C(diamond) or compound semiconductors. The innovative process as called CMG(Chemo-Mechanical-Grinding) for Si wafer has been recently developed which is different from conventional CMP(Chemo-Mechanical-Polishing ) process. The CMG process can be done under dry conditions using CeO2 based solid bulk abrasives. The microstructures for surface and subsurface of Si single crystal after CMG process were analyzed using TEM/EDX, AFM, MFP-3D Microscope. The mechanism of CMG process was also investigated by X-ray diffraction and ICP chemical analysis using products by chemical reaction between Si and CeO2 abrasives. The results showed that Si single crystal after CMG had, 1) no defects even Si lattice revel or mechanical imperfections,2) better surface roughness as compared to CMP process. The CMG mechanism concluded that CeO2 reacted with Si producing Ce-Si-O amorphous phase.