Abstract:Cubic β-SiC coating was grown onto the graphite substrate by the normal pressure chemical vapor deposition using CH₃SiCl₃ (MTS) as a source precursor at 1 150 ℃. But the hexagonal Al₄SiC₄ phase was generated in the doped process with trimethylaluminium (TMA) as the dopant. Microstructure of the deposit coating as-prepared was characterized by scanning electron microscope (SEM), which consists of spherical particles with a very dense facet structure. The real component of permittivity ε′ and dielectric loss tanδ of the coatings undoped and doped by TMA were carried out by a vector networ, k analyzer in the microwave frequency ranges from 8.2 GHz to 12.4 GHz. The results show that both of them have low values, and doped coating has lower ε′ and tan δ than undoped one due to the existence of Al₄SiC₄ impurity phase, which indicates that the desired Al/SiC solid solution at 1 150 ℃ in a normal argon atmosphere is not produced.

Key words: silicon carbide; aluminum doping; dielectric properties; chemical vapour deposition