Cryogenic reactive ion etching (RIE) of silicon using SF6 gas and a multilayer Ni/Al mask has been studied and high-rate, directional deep etching was demonstrated. The temperature of the cathode wafer stage was controlled at a low temperature (-60 degrees C) and a magnetic field was applied to enhance the plasma density. A high flow rate (1 sccm) of the etching gas and low pressure (0.5 Pa) produced by high-speed exhausting were effective for high-rate etching and directional etching. A trade-off of the RF power density was necessary between the etching rate and the etching selectivity to the mask with selectivity improving at higher etch rates. The system could be used to etch through a silicon wafer of 200 mu m in thickness. An etching rate of 0.8 mu m min-1 and vertical walls as thin as 20 mu m were obtained in the through wafer etching. On the other hand, the etching rate was reduced in narrow deep grooves. This etching method is effective in fabricating three-dimensional silicon microstructures with high aspect ratio.
We have developed a laser and focused ion beam (FIB) compound system to process an optical component device with an ultrafine precision minute surface structure and a micromedical device. This machine consists of an FIB and three types of lasers with an atomic force microscope. This system can fabricate decamicrometer area by laser and submicrometer area by FIB at one chuck. When processing the press mold die of a microlens array (10x10) in a glasslike carbon with a femtosecond laser, a diameter of 3.2 microm and depth of 0.43 microm are obtained. However, the surface roughness is more than Rz=0.5 microm. After this process, we finished this surface with the use of the FIB. As a result, the surface roughness is less than Rz=0.05 microm.
A local vacuum system for focused ion beam (FIB) processing, with a workpiece set in the air, has been developed. The local vacuum apparatus had a double-wall cylinder structure, used a differential exhaust, and each cylinder was connected to a vacuum exhaust pump. When the gap between the workpiece and the apparatus was 10 microm, the pressure of beam line in the machining head achieved 2.1 x 10(-3) Pa. In addition, a visualization system was developed by visualizing the current flow out from a sample by FIB irradiation. With this system, it is possible to conduct focus adjustments of the FIB and shape recognition on a workpiece in the order of microns.
A transparent acrylic resin, which is often used for cosmetic surface materials and acoustic insulation materials, was investigated to experimentally evaluate the effect of the concavo-convex shape transmittance and haze. The surface of an acrylic resin plate was shot-blasted using spherical glass beads to alter the various surface roughness by changing the projection pressure. The shot blasted surface was comprehensively evaluated using the areal surface texture including height, spatial and hybrid parameters to clarify the surface texture characteristics. As a result, the effect of the surface texture on the visual texture was apparent as a tendency for increased haze as the arithmetic mean height increased. Furthermore, the root mean square slope, Sdq had a high positive correlation to the haze.
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