Yongsheng Ren¹, Kazuki Morita¹; ¹The University of Tokyo

A novel attempt was made to remove B from Si by adding Zr as the trapping agent in solidification refining using a Si-Cu solvent. The premise of the study was based on the following: (i) low solid solubility of Cu in Si; (ii) significant density difference between Si and liquid Si-Cu; (iii) lower liquidus temperature of the Si-Cu system; (iv) high affinity of Zr to B for enhanced formation of boride. First, the solubility product of ZrB₂ in the Si-Cu melt was measured as 4.11 \\215 10⁻¹² (1345 K, Si-50 at.% Cu) and 2.55 \\215 10⁻¹² (1258 K, Si-57 at.% Cu). ZrB₂ precipitation was found at the bottom of the sample. Additionally, solidification refining experiments were carried out under different variables. The maximum removal fraction of B was 93.4%; further, the added Zr was almost completely eliminated and did not contaminate the refined primary Si.