Cost-effective preparation of high-quality silicon nitride powders from silicon scrap through direct nitridation

This work reports a cost-effective and environmentally friendly method for preparing high-quality and highly-crystalline silicon nitride (Si3N4) powders from silicon (Si) scrap through direct nitridation. With Si scrap from semiconductor manufacturing processes being a critical and imperative global issue in recent times, an efficient methodology is essentially required to recycle it. For this purpose, ball milling parameters for Si scrap were optimized using different solvents to obtain homogeneous and fine-micron sized silicon powders for efficient nitridation. Ethanol was found to be the most effective in producing the required conditions of Si powders. Direct nitridation was performed at 1450 °C in an atmosphere of nitrogen and hydrogen gas flow to prepare Si3N4 powders. Various characterization techniques were used to analyze particle sizes, phase compositions, and morphologies of raw Si scrap, ball-milled Si powders, and Si3N4 powders. Results indicated that the nitridation reaction resulted in 90.1% conversion of Si into Si3N4 and the α-Si3N4 phase accounted for 85% of the total Si3N4 produced. This study provides a fundamental perspective from both industrial and environmental standpoints on the recycle of Si waste and production of cost-effective and high-quality Si3N4 powders. This novel approach of using Si scrap as a silicon source for Si3N4 powder preparation has the potential to significantly reduce the large volumes of Si waste generated from semiconductor industries.