松坂 壮太

There have been many investigations into the changes in the properties of transparent materials, e.g. optical, physical and chemical properties, induced by focused ultrafast laser beams. In this letter, we report the modification of borosilicate glass using an ultraviolet nanosecond laser. A laser beam operating at a wavelength of 266 nm was focused inside the glass. Interestingly, although penetration depth of the laser beam was only 110 μm, emission was observed in the glass at the depth of approximately 1100 μm after several laser shots. The emission moved toward the light source with further laser illumination, and modification of the glass along the trajectory of the emission was observed. The modified area became deeper with increasing focusing depth. The deepest modified area was located at a depth of approximately 1800 μm. No clear dependence of the modification on the pulse repetition rate was found; therefore, heat accumulation was not prominent in the modification process. The subsequent etching rate of the modified area was faster than that of the unmodified area. The etching rate in aqueous KOH was 60 μm/h where continuous modification was obtained. A microchannel with a depth of approximately 400 μm and a diameter of approximately 30 μm was formed after 10 h etching.

The crack propagation behavior and the internal stress field during mechanical cleavage of non-alkali glass sheets (thickness : 0.7mm) were visualized by high-speed imaging techniques. At first, the effect of scribing conditions on the fractured surface quality was investigated when the scribing wheel with surface asperities was used. It was found that the surface quality was strongly influenced by an applied load. In the case of low load conditions (∼11N), the fractured surface exhibited rugged patterns known as 'hackle', and it gradually changed to regular striped pattern known as 'ribmark' with the increase of applied load (12N∼). In order to understand the reason why the surface quality changed with the applied load, the crack propagation behavior was observed using a high-speed camera. The results showed that the generated crack hardly propagated to thickness direction when the applied load was low, in contrast to the rapid propagation under the high load conditions. Because the crack propagation behavior was likely determined by the stress field around the generated crack, the phase difference measurement, which was proportional to the principal stress difference, was conducted using a high-speed polarization camera. The results showed that the phase difference gradually vanished, i.e. the stress relaxation occurred, with the crack propagation especially in the high load conditions. By the image analysis for obtained phase difference from the polarization camera, an in-process estimation method of fractured surface quality was proposed.

In this study, we propose the new equations which predict cutting forces under the conditions of a small feed (2.5μm) and negative approach angle. They are based on Nakayama's equations. According to our previous research, the experimental cutting forces were larger than the calculated forces with Nakayama's equations. The differences were caused by size effect. One of the causes of size effect was a cutting edge radius. Therefore, the new equations were formulated with taking into account the cutting edge radius. The cutting force calculated by the new equations were approximately equal to the experimental results. The accuracy of the new equations is validated under the conditions of thrust force free cutting.

In order to improve the laser micro-machinability of borosilicate glass, the glass surface was doped with metal (silver or copper) ions by electric field-assisted solid-state ion exchange. Doped ions drifted and diffused into the glass substrate under a DC electric field. The drift-diffusion behavior of metal ions in glass was numerically analyzed using standard explicit finite-difference method. The calculated penetration depths of both silver and copper showed good agreement with experimentally measured values. However, there was a difference between measured and calculated ionic fluxes, especially for the early-stage of ion exchange. This discrepancy was likely to be caused by an imperfect initial contact between metal foil and glass substrate. Therefore, the increase in electric current path with ion exchange time was necessary to be taken into consideration. The modified calculation enabled more accurate estimation of ionic penetration depths.

本研究では，卓上精密旋盤を用いて形状精度の高い微細軸を作製する手法について検討した．旋削加工を行う際に生じる切削力のうち，背分力は軸の寸法や形状精度に影響を及ぼす．旋削条件のうち，工具のノーズ半径，アプローチ角および切込み量を適切に設定することで背分力を抑制する加工条件について検討した．その結果，背分力をゼロに抑制することが可能であることを示し，軸径50μm，長さ1mmの微細軸を旋削加工により作製することが可能であることを示した．また，切削抵抗に関する実用式と実験結果の比較を行い，その差異の要因について検討した．

本研究では，ガラス管を用いて，穴底部にレーザ光と水を同時に供給する穴あけ法を開発した．ガラス管の一端にレーザ光と水を供給すると，レーザ光はガラス管内を全反射し，ガラス管の反対側端面から水と同時に加工部に照射される．穴への管の挿入で，穴底部へ高エネルギの光の照射が可能になる．また，水を流すことで，デブリの排出も容易となる．実験装置の試作およびガラス管内をレーザ光を効率よく導波させるために導波解析を行った．本手法により，天然ゴムに穴径2.0mm，穴深さ30mmの穴加工を行った．また，曲がったガラス管を用いることで，曲がり穴加工を実現した．

A laser forward transfer technique of gold nanoparticles (GNPs) deposited on glass substrates to silicon wafers and periodic patterning of transferred GNPs is demonstrated. Gold colloidal solution was prepared by citric acid reduction method. The GNPs were deposited by immersing glass substrates derivatized with (3-aminopropyl) trimethoxysilane (APTMS) in the gold colloidal solution for 0.5 h - 3 h. Dispersed or aggregated GNPs were deposited by using Gold colloidal solution with different concentrations. The glass substrate deposited with the GNPs was placed on a Si substrate. The GNPs deposited side was faced to the Si substrate. Then GNPs were illuminated with the second harmonic wave of Nd : YAG laser through the glass, as a result the gold nanoparticles were transferred to the Si substrate. The GNPs deposited on the silicon surface was sphere and dispersed, nevertheless, they were aggregated on the glass surface before transferring by the laser illumination. After the illumination of the Nd : YAG laser to the silicon surface with the GNPs, the periodic deposition of Au was observed. The periodic spacing of the Au were depended on the wavelength and incident angle of the laser beam.

To remove dust particles accumulated on pad surfaces or probe tips after they contact each other during semiconductor wafer testing, a cleaning process is required. On the one hand, scrubbing is an efficient method to remove the oxide layer on the surfaces. However, excessive scrubbing degrades the probe's mechanical properties and leads to the accumulation of excessive dust and plastic deformation failure of the pad surface. Therefore, we have developed a new contact probe that allows only a vertical displacement of the probe tip on the pad surface to minimize the horizontal displacement for scrubbing. This probe is fabricated using a beryllium-copper alloy and is characterized by a two-beam structure. The matrix method is employed to investigate the contact probe structure and the results are compared with the data obtained with a commercial finite element method. Furthermore, electrical contact resistance is measured experimentally and determined theoretically using Holm's theory. A durability test is conducted to simulate more than 100,000 contacts between the probe tip and the pad; this allows us to examine the probe tip's endurance and whether the electrical resistance of the contact could be sustained. Our results suggest that the two-beam structural probe ensures a stable electrical contact resistance when the contact force is within specific limits and the horizontal displacement for scrubbing is minimized.

The fusion splicing of ribbon-shaped eight optical fibers was carried out with CO_2 laser beams. At first, laser beam of uniform power distribution, which was obtained by simple aperture method, was irradiated to every fiber. However, defective connections were frequently occurred at both edges of the ribbon fibers, because the heat inputs to these fibers were low and not enough to melt silica glass fibers. Two-dimensional heat conduction analysis indicated that the reason was the large heat transfer and radiation from these fibers to atmosphere. Therefore, higher laser power was necessary to be supplied to two edge fibers. Laser beams designed specially, which had about 20〜22% higher power density at edge region, enabled the temperatures of all fibers to reach their softening point simultaneously. As a result, excellent connections with low splicing loss of 0.011dB on average values were achieved.

Micromachining of silicon was investigated using the fourth-harmonic wavelength (λ=266 nm,τ=6ns) of a pulsed Nd: YAG laser beam. The beam was irradiated onto a silicon workpiece under flowing water. The drilled surfaces were then characterized using an optical microscope, laser interference microscope and a scanning electron microscope. Compared with atmospheric machining, problems, such as debris and reattachment of molten material, were improved clearly and dramatically. Machining under water produced a somewhat smoother ablated surface because the molten silicon was rapidly solidified. When the focal point was set over the surface, the ablated shapes after laser irradiation were irregular because water evaporation caused unstable ablation. On the other hand, stable ablation was produced when the focal point was set under the surface. The relationship between the irradiation parameters and the resulting shape became quantitatively clear from the experiment.