Dielectric properties of chemically vapour-deposited Si₃N₄

Abstract

The dielectric properties of chemically vapour-deposited (CVD) amorphous and crystalline Si₃N₄ were measured in the temperature range from room temperature to 800° C. The a.c. conductivity (σ _a.c.) of the amorphous CVD-Si₃N₄ was found to be less than that of the crystalline CVD-Si₃N₄ below 500° C, but became greater than that of the crystalline CVD-Si₃N₄ over 500° C due to the contribution of d.c. conductivity (σ _d.c.). The measured loss factor (ɛ″) and dielectric constant (ε′) of the amorphous CVD-Si₃N₄ are smaller than those of the crystalline CVD-Si₃N₄ in all of the temperature and frequency ranges examined. The relationships ofε″ αω ^n-1, (ε′-ε′ _∞) αω ^n-1 andε″/(ε′-ε′ _∞) = cot (nπ/2) (were observed for the amorphous and crystalline specimens, where ω is angular frequency andn is a constant. The values ofn of amorphous and crystalline CVD-Si₃N₄ were 0.8 to 0.9 and 0.6 to 0.8, respectively. These results may indicate that the a.c. conduction observed for both of the above specimens is caused by hopping carriers. The values of loss tangent (tanδ) increased with increasing temperature. The relationship of log (tanδ) ∝T was observed. The value of tanδ for the amorphous CVD-Si₃N₄ was smaller than that of the crystalline CVD-Si₃N₄.