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RECYCLING OF SILICON-WAFERS PRODUCTION WASTES TO SIALON BASED CERAMICS WITH IMPROVED MECHANICAL PROPERTIES
The output of highly pure semiconductor silicon for integrated circuits and memories is increasing year by year. During wafer production process, about 60% (2,400 tons) of silicon, ingot after trimming, is scrapped with the waste water disposal from cutting and polishing. The recycling to highly pure silicon is very costly. If the silicon sludge can be converted to nitride-based structural ceramics (SiAlON), it is helpful for semiconductor industry and ecological problems.
A high-temperature SHS reactor capable of operating at a maximum pressure of 300 psi was designed, developed, and successfully tested. Silicon wafers production wastes were collected and characterized for particle size, phases using X-ray diffraction (XRD), and morphology of the particles using scanning electron microscopy (SEM). The silicon sludge was milled into fine particles and subsequently converted into ®-SiAlON ceramic by high-temperature SHS reaction. The XRD results clearly show that only 50% of the silicon sludge was converted into ®–SiAlON due to low nitrogen pressure. The ®-SiAlON powder was then mixed with 25 wt % of Y2O3-stabilized ZrO2, consolidated into pellets, and sintered to 92% of the theoretical density at 1,600°C. These materials exhibited a maximum Vickers hardness of 4.6 GPa, which is much lower than the expected value of 12–15GPa. Through this project it was demonstrated that it is possible to convert silicon wafers production wastes into ®-SiAlON ceramics by high-temperature SHS reaction. However, it was observed that the complete conversion of silicon sludge into ®-SiAlON requires a higher nitrogen operating pressure than the present SHS reactor system. The SHS autoclave was also tested for other potential ceramic material development such as TiN from Ti or AlN from Al waste.