Formation process of Si₃N₄ particles on surface of Si ingots grown using silica crucibles with Si₃N₄ coating by noncontact crucible method

A noncontact crucible method was used to investigate the process by which a Si₃N₄ coating material forms Si₃N₄ particles or precipitates on the surface of Si melts and ingots. Si ingots were grown using crucibles with and without a mixture of α- and β-Si ₃N₄ particles. The oxygen and nitrogen concentrations in the ingots were measured by Fourier transform infrared spectrometry analysis. The nitrogen concentration in the ingots grown using crucibles with a Si ₃N₄ coating was significantly higher than that in ingots grown using crucibles without a Si₃N₄ coating because the nitrogen from the Si₃N₄ coating material dissolved into the Si melt. From orientation image maps analyzed using electron backscattering diffraction patterns of Si_xN_y particles on the surface of the ingots, it was clarified that most of the Si_xN_y particles were β-Si₃N₄. This was also confirmed by X-ray diffraction measurements. The Si₃N₄ particles on the surface of the ingots had several morphologies such as needle-like, columnar, leaf-like, and hexagonal structures. There were two cases in which floating Si₃N₄ particles were formed on the surface of the Si melts, i.e., the removal and dissolution of the Si₃N₄ coating material. The removed or dissolved Si₃N₄ coating materials, which consisted of a mixture of α- and β-Si ₃N₄ particles, are considered to have finally changed into β-Si₃N₄ in the form of transformers or precipitates on the surface of the Si melt, and these β-Si₃N₄ particles became attached to the surface of the ingots.