Kenji Furuya

SYNTHESIS OF LARGE-SIZE BETA -SI3N4 CRYSTALS

Large-sized β–Si 3 N 4 crystals up to 10 mm in length and 0.3 mm in diameter with low impurity concentration are successfully grown from silicon melt in a nitrogen atmosphere. By controlling the concentration of impurities in the silicon melt, a new kind of β–Si 3 N 4 crystal, that is, a transparent coloring one with an absorption edge around a wavelength of 520 nm, is obtained.

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

Two kinds of obviously different-sized –Si 3 N 4 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 Si 3 N 4 whiskers were grown from the surface of the SiC particles within the Si melt. The large Si 3 N 4 whiskers were grown from the surface of Si 3 N 4 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 Si 3 N 4 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–Si 3 N 4 single crystals.