Recycling high-purity silicon from diamond-wire saw kerf slurry waste by vacuum refining process

Abstract

Approximately 35%–40% crystalline silicon becomes silicon powder waste (SPW) when producing silicon wafers. Substantial amount of SPW will be produced as the demand for wafers increases. Recycling Si from SPW for preparing silicon has been a significant issue. Considering the current recovery ratio of SPW is low, it is urgent to investigate an effective method to recycle SPW. In this paper, SPW was re-melted into high-purity silicon ingots by vacuum refining process and the recycling process involved two stages. In the first stage, SPW was pelletized by a double-roll type presser. In the second stage, the pellets were melted into high-purity silicon ingots by vacuum refining. The effects of the smelting time and atmosphere condition on the silicon recovery ratio, and the influence of the smelting time on impurities removal ratio were investigated. The maximum silicon recovery ratio could be increased from 56.5% by atmosphere smelting to 68.65% by vacuum smelting. Si ingots with a purity of 99.65%, B 0.21 ppmw and P 3.03 ppmw were prepared. The melting mechanism of the silicon powder and economical evaluation were also discussed in this paper. The recovery of SPW by vacuum refining can not only realize resource reutilization but also bring about economic benefits ($0.406/kg) at laboratory-scale.