Effect of the Pretreatment Step Condition in the Growth Process of the Si Melt Method on the Size of β–Si₃N₄ Single Crystals

Abstract

Two kinds of obviously different-sized –Si₃N₄ whiskers were grown from silicon melt with different pretreatment vacuum conditions. Their growth interface structures were studied in a cross-section view from micro-areas to macro-areas by combination of micro-area state analysis with chemical shift mapping of Si K_β bands using electron probe microanalysis. The one pretreated under the lower vacuum condition with a rotary pump was 10–20 μm in diameter and hundreds of micrometers in length, and another pretreated under the higher vacuum condition with a diffusion pump was 0.1–0.2 mm in diameter and 2–5 mm in length. The small Si₃N₄ whiskers were grown from the surface of the SiC particles within the Si melt. The large Si₃N₄ whiskers were grown from the surface of Si₃N₄ crucible. On the basis of these results, their growth mechanisms are discussed from the view of the nucleation sites, impurity source, and thermodynamic stability of the SiC particles. Compared with the Si₃N₄ grains, the SiC particles influenced the nucleation deeply and caused the process to grow small-sized crystals. Preventing the carbon impurities into the Si melt from forming the SiC particles in the pretreatment process was one effective way to grow the large-sized β–Si₃N₄ single crystals.