Osamu Ohnishi

Fabrication of Electroplated Micro Grinding Wheels and Manufacturing of Microstructures with Ultrasonic Vibration

This study presents the fabrication of micro cylindrical diamond gr inding wheels with diameters from 100 to 500 μm by electroplating of diamond grits in a W atts bath and the manufacturing of micro-structured surfaces assisted by ultrasonic vibration. As a substrate material for micro electroplated wheels, ultra-fine grain cemented carbide was chosen to make the tools more rigid. The fabrication process of the micro wheels consists of cle aning the substrate surface and electroplating the diamond grits. In the present work the electrolyt ic degreasing is performed in addition to the conventional cleaning. This degreasing is found to be effec tive to enhance the adherence between substrate material and electroplated layer. The best adherence is obtained at a degreasing time of 5 min. Using the fabricated wheels, drilling and grooving of sil ic n and stainless steel were performed. In these machining processes application of ultrasonic vibration helps to reduce the wheel loading and sometimes minimizes the dropping of grits from the tool sur face.

Study on the Development of Resource-Saving High Performance Slurry - Polishing/CMP for Glass Substrates in a Radical Polishing Environment, Using Manganese Oxide Slurry as an Alternative for Ceria Slurry

While investigating polishing mechanism of glass substrates with ceria abrasives (CeO2), we found its oxidizing properties worked effectively for the polishing. This finding has inspired us to speculate about the possibility of the manganese oxide abrasives as an alternative for ceria as they also have oxidizing properties. Therefore, focusing on the valence of the manganese, we have experimentally manufactured MnO, MnO2, Mn2O3 and Mn3O4 abrasives, and conducted a comparison study of the characteristics obtained with ceria slurry and manganese oxide slurries. As a result, the surface roughness of below Ra 0.8nm obtained with Mn2O3 slurry was found better than that with the conventional ceria slurry, on top of which, its removal rate was as good as or equal to that of ceria. Using a novel, closed type CMP (Chemical Mechanical Polishing) machine, we conducted another glass polishing experiment with ceria and manganese oxide slurries. The inside of the CMP machine was filled with high-pressure gases such as oxygen, air and nitrogen and kept at 500kPa to make the polishing environment radical. Through this experiment, we found an effective polishing method for high-quality surface. The removal rates were several times better than that of the conventional polishing performed in an open CMP machine.

Analysis of Chemical and Mechanical Factors in CMP Processes for Improving Material Removal Rate

As the design rules for electric microdevices gets smaller, the requirement for the production process gets more severe. For example, the nanolevel defect free with a higher throughput performance is required for chemical mechanical polish (CMP). To achieve such a level of requirement, slurry and process development based on the mechanism needs to be done. In this study, the platen motor current was monitored and used to establish an energy model for material removal rate during CMP. By using the motor current as a measure of friction, the conversion of abrasion and heat to the mechanical energy was modeled. The results show that, for silicon dioxide layer obtained by plasma-enhanced chemical vapor deposition from mixture of reactive gases such as oxygen and tetraethoxysilane (PE-TEOS), silicon nitride, and silicon, the material removal rate is dominated by the mechanical energy independent of slurry properties such as pH, particle size, or material. As a result, maximizing the friction (i.e., motor current) during CMP is a key parameter in maximizing the material removal rate. Using this method, it was determined that, in addition to size, the irregularly shaped abrasive has an advantage over the spherical shaped abrasive.

Performance of micro PCD drills in drilling into SiC and effects of ultrasonic vibration

The present paper deals with the micro drilling into silicon carbide (SiC) with micro polycrystalline diamond (PCD) drills. Micro PCD drills with a nominal diameter of 300 μm were fabricated by wire electrodischarge machining and they were used to drill into SiC test pieces with or without ultrasonic vibration. In the drilling test, performance of drilling into SiC was investigated. As the result of the drilling test, it was possible to make holes with good shape under all conditions. Large feed condition led to large chipping around hole entrance, bad surface roughness of hole wall and a shortened tool life. On the other hand, effects of ultrasonic vibration on chipping, surface roughness of hole wall, chip form and tool life were unclear, but the surface appearance of holes drilled with ultrasonic vibration did not seem to be affected so much by increase of feed.

Chapter 6 – Lapping and Polishing

The processing technology has beeu applied to the fabrication of optical, electrolic, and mechanical devices. A study on an automatic or computer-aided machining system or both processing and ultraprecision polishing has been undertaken for practical use. In this chapter, principles of lapping and polishing for hard and brittle materials, like optical glass and crystals belonging to the groop of ceramics, are discussed including the ultraprecision processing technique.

Basic Study on Etching Selectivity of Plasma Chemical Vaporization Machining by Introducing Crystallographic Damage into Work Surface

Plasma chemical vaporization machining (PCVM) is a high-speed plasma etching method using atmospheric-pressure plasma. Although it does not leave an affected layer on the processed surface because of the small ion energy owing to the small mean free path of gas molecules, it is not suitable for planarization because of its isotropic etching. Thus, a combination of PCVM and a mechanical machining process is proposed. The convex parts of a substrate surface are considered to be affected by mechanical machining and are removed preferentially by PCVM. In this report, it is investigated whether etching rate of the affected layer becomes larger or not. As a result, it was found that the etching rate increased in the first 100 nm depth of the mechanically polished substrate, which corresponds to the thickness of the heavily damaged layer observed by cross-sectional transmission electron microscopy.

Fabrication of Micro Ni-W Electroplated Diamond Tools and Their Application to Grooving of Brittle Materials : Improvement of Tool Quality and Machining Performance

The present paper intends to improve the tool quality and the machining performance of micro cylindrical Ni-W electroplated diamond tools. From the grooving tests of silicon the following results were obtained. The scatter of diamond grit density on the tool surface can be prevented through the intermittent pouring of electroplating solution into the solution with grit supported by a filter. Ni strike plating before electroplating is useful for extending the tool life, but it can result in the degradation of roughness on groove side surface. Tool wear may result from the removal of bond material due to generated chip and dropped diamond grit, therefore the usage of harder bond material and the heat treatment of bond material are recommended. For a constant tool diameter there exists a suitable grit diameter from the viewpoint of machining efficiency and groove roughness. In grooving of quartz glass, chippings of 10-20μm may occur on the groove edges, which can be prevented by the application of axial ultrasonic vibration to the tool.

Effects of atmosphere and ultraviolet light irradiation on chemical mechanical polishing characteristics of SiC wafers

To establish a high-efficiency and high-quality polishing process by controlling the workpiece environment, a prototype chemical mechanical polishing (CMP) machine that can perform double-side CMP simultaneously in a sealed pressure chamber was developed. Using this new machine, polishing experiments on single crystalline silicon carbide (SiC) wafers were carried out. The results showed that applying a highly pressurized O2 gas and ultraviolet light irradiation were effective in SiC CMP.

Effect of Groove Pattern of Chemical Mechanical Polishing Pad on Slurry Flow Behavior

In chemical mechanical polishing (CMP), the slurry flow behavior on the polishing pad is very important both for improving polishing effectiveness and for reducing the slurry consumption. In this study, we aim to evaluate two types of CMP pad that have unique special groove patterns, slurry outflow and inflow pads, for controlling the slurry flow behavior. We describe the effect of the groove patterns on the slurry flow behavior observed using images recorded using a high-speed digital camera. The results of the study indicate several advantages of the proposed pads over the conventional pads from the viewpoint of slurry flow behavior.

Performance Evaluation Method of Chemical Mechanical Polishing Pad Conditioner Using Digital Image Correlation Processing

In chemical mechanical polishing (CMP), conditioning is generally used for the regeneration of the pad surface texture. Currently, the performance evaluation of conditioners depends on the users experience so that it is important to develop a novel quantitative evaluation method for conditioner performance. In this paper, we propose a novel evaluation method for conditioner performance using digital image correlation (DIC) processing. The proposed method can measure the in-plane micro-deformation distribution of the pad surface texture by conditioning. It is found that a pad surface deforms over 40 µm with conditioning and that the in-plane deformation value increases with a decrease in the mesh size of conditioner grains.