Low-Temperature Process for the Fabrication of Low-Boron Content Bulk Si from Si–Cu Solution with Zr Addition
Yongsheng Ren, Kazuki Morita
Abstract
A novel approach was put forward to remove B from Si by utilizing Zr as an additive during solidification, whereby, using the Si–Cu solvent, bulk Si with large area and low boron content was obtained. The premise of this work is based on the following parameters: (i) the lower liquidus temperature of the Si–Cu system; (ii) the notable density difference between solid Si and liquid Si–Cu; (iii) the low solubility of Cu in solid Si; and (iv) the strong affinity of Zr for B, enhancing boride formation. The experimental results show that (i) intermediate ZrB2 compounds were found at the bottom of the sample; (ii) the B-removal fraction improved significantly, the highest of which was 93.4%; (iii) large areas of bulk Si were obtained, and a high Si enrichment percentage of 99.2% was achieved; (iv) the residual Cu content was reduced to a relatively low level, the molar fraction of which ranged from 0.00099 to 0.00191; and (v) the Zr additive was completely removed and did not pollute the refined Si. This one-step directional solidification process provides a better alternative for Si-based solvent refining to produce solar-grade silicon for use in the photovoltaic industry.