Microstructure and Physical Properties of New SiC Materials with High Thermal Conductivity

Abstract

ABSTRACTSilicon carbide materials with BeO addition (2 wt%) have the unique properties of high electrical resistivity, high thermal conductivity, and a thermal expansion coefficient close to that of silicon. The materials have been used as a chip carrier material for high power LSI packaging. Microstructures were correlated by means of analytical electron microscopy (AEM), with the physical properties. Generally, BeO particles are evenly distributed mostly at triple points and the grain growth is anisotropic and many grains are elongated with an aspect ratio of 2 or 3. The average grain size is measured to be around 5 μm and the morphology is typically thick tabular.AEM analysis has shown that large middle section of each SiC grain is mostly 6H polytype with a few or no stacking faults. On both sides of the 6H polytype, sheaths are formed, which consist of a large number of extremely thin 4H or other polytype lamellae. Along grain boundaries, no second phase formation is observed with a few exception of Be 2 C and impurity transition metal compounds lamellar formation.The results indicate that direct and clean contacts between 6H lamellae and BeO grain or other 6H lamellae form a path of high thermal conductivity. On the other hand, complex network of thin disordered (4H rich) lamellae doped with BeO forms the electrically high resistive path.