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山田, 啓司 ; 西岡, 真吾 ; 細川, 晃 ; 上田, 隆司
概要:
Laser cleaving process is a prospective technique to divide a thin plate of brittle materials into small pieces, because of its high yield ratio and controllability. In addition, the process is carried out without coolant which
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causes the environmental pollution and the contamination of the electrical devices etched on the wafer. In this paper, laser cleaving of silicon wafer is conducted with pulsed Nd: YAG laser. The temperature of laser spot is measured by means of the two-color pyrometer with optical fiber and the acoustic emission caused by crack propagation is also observed. When the laser spot is scanned at the appropriate interval and velocity, the crack propagates in sequence by the corresponding laser irradiation. As a result, both high linearity of cleaved edge and fine fractured surface roughness are obtained. The thermal stress distribution induced by laser irradiation is analysed with FEM model, in which the stress intensity factor is calculated at the vicinity of the crack tip in order to clarify the criterion of crack propagation. The analysis and experiments reveal that the maximum tensile stress at the crack tip increases with temperature and the crack propagates when the stress intensity factor reaches the fracture toughness of the material.
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| 2.
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山田, 啓司 ; 森田, 精一 ; 上田, 隆司 ; 細川, 晃 ; 田中, 隆太郎
概要:
In this paper, a refrigerating chuck system is developed to reduce the thermal damages of workpiece in laser cleaving process. The system reduces the surface temperature of table below the freezing point of water, and the work material is
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fixed on the table by the frozen water between the material and the table. The cooling capability of the system is investigated. The system is applied to the laser cleaving process of silicon wafer with cw-Nd:YAG laser. The laser cleaving experiment of silicon wafer is conducted with Nd:YAG laser, then the width of thermal affected zone on the irradiated surface, the roughness of fractured surface and the deviation of cleaving trajectory are measured. The silicon oxide is caused on the surface of wafer in the room temperature, but the refrigerating chuck can prevent the thermal damage and improve the reliability of the cleaving process. By use of the chuck, the smooth fractured surface is achieved and the linearity of the cleaving trajectory is also improved.
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山田, 啓司 ; 大礒, 桂一 ; 細川, 晃 ; 上田, 隆司
概要:
The thermal stress cleaving of silicon wafer with a laser beam is a prospective technique, which supersedes the mechanical dicing. This method makes it possible to cut a wafer at very high production rate in comparison with the diamond thin
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blade wheel and to protect the wafer from the contamination of cutting coolant and chips. In this paper, the cleaving mechanism of silicon wafer irradiated with the pulsed Nd:YAG laser is investigated. The temperature at the area irradiated with laser is measured using two-color pyrometer with an optical fiber. The acoustic emission is also measured to examine the mechanism of the crack propagation. In the process, the temperature at the area irradiated with laser should be controlled in order to reduce the thermal damages and to improve the cleaving accuracy.
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山田, 啓司 ; 加藤, 寛満 ; 上田, 隆司 ; 細川, 晃 ; 田中, 隆太郎
概要:
Micro machining of single-crystalline silicon is performed with the second-harmonic of Nd:YAG laser in this study. In experiments, various shapes of plastic microlens are fabricated on a transparent substrate by the developed
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die-less method. These microlenses are shaped by thermal deformation induced by the Er:YAG laser beam absorbable for the acrylate resin. And then, these lenses are used as optical devices to generate the local high energy density desired for machining of silicon in air and water. Machining characteristics are investigated in the single groove machining process, and the grid groove pattern and the herringbone pattern are formed to demonstrate the feasibility of proposed methods.
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坂谷, 勝明 ; 黒部, 利次 ; 鈴木, 繁成 ; 廣崎, 憲一
概要:
A new type of field-assisted fine polishing method for brittle materials has been proposed, which is developed for applying to the polishing on NC grinding machine without the vessel for polishing compound. In this method, the
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non-contact type polishing is realized with fluid grinding wheel which is covered with thick magnetic fluid film holding the abrasive grain. In this report, the surface polishing experiments are conducted on silicon wafers and the polishing characteristics are examined. The following results are obtained : (1) When the clearance between the polisher and the work surface exceeds the definite value, the polishing rate decreases extremely. (2) The use of water based magnetic fluid yields lower polishing rate but smoother surface in comparison with kerosene based magnetic fluid. (3) The surface roughness of polished surface basically depends on grain size and the roughness of the order of nanometers is obtained with fine abrasive grain.
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黒部, 利次 ; 野口, 通一 ; 松本, 貴宏
概要:
This paper describes some experiments for breaking a silicon wafer precisely using YAG laser. The popular mechanical cut
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ting of a silicon wafer using a diamond blade is not always high quality. The noncontact cutting of ceramics using CO2 laser is recently being studied enthusiastically. The precise breaking of a silicon wafer, however, has never been achieved. In the experiments, the conditions and the quality of double irradiation breaking are searched in various atmospheres. It is found that air cooling, water cooling and assist gas method has similar breaking forms. Main crack meanders and it is accompanied with some branching cracks which deteriorate the breaking quality of a silicon wafer. However, local cooling method enabled high quality breaking. The measurement results of the surface roughness of cross section are extremely small, 0.003-0.004 μm at Ra. It is also shown that the crack propagation velocity of local cooling breaking is about 10m/s higher than that of other ones.
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黒部, 利次 ; 山下, 勝久 ; 坂谷, 勝明
概要:
Magnetic field-assisted fine polishing method has been proposed, which uses a magnetic slurry mixed non-ferrous abrasives into a magnetic fluid. Polishing machine has newly been developed which is consisted both of copper rotary disc
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set a strong permanent magnet and a rotary shaft set similar one, it is mounted a specimen to be polished. Magnetic field strength controlled by moving their magnets is responsible for yielding superior surface quality. It is found that polishing machine has high performance finishing ability and the usage of a variety of magnetic fluid is proposed versatile polishing characteristics. Experiments show that kerosene based magnetic fluid has very high polishing performance compared with water based one. The usage of coarse grain gives rise to increase the surface roughnes, and larger clearance between specimen and copper rotary disc lowers finishing rate of wafer in kerosene based magnetic fluid especially. Movement of permanent magnet in copper rotary disc is very effective for finishing of wafer.
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