Growth of 2-inch diamond films on 4H–SiC substrate by microwave plasma CVD for enhanced thermal performance

We report a novel method of producing composite substrates by growing diamond films on a 4H–SiC substrate by microwave plasma chemical vapor deposition to enhance the thermal management for thermal diffusion applications in GaN-based RF power devices. Morphology, grain orientation and structure of the diamond films were characterized by scanning electron microscopy, electron backscatter diffraction, X-ray diffraction and Raman spectroscopy. The diamond films were uniform and compact, without voids and gaps observed via cross-sectional view of microscopy, and without any graphite phase and impurity peak. Thermal conductivity (TC) of the diamond-SiC composite substrates was simulated and calculated. Results indicate that the TC of the composite substrates is up to 512.02 ± 6.37 W m−1 K−1 when the SiC thickness is 500 μm, which is 1.53 ± 0.02 times of the pure SiC substrate, and this high TC increases to 1171.13 ± 67.23 W m−1 K−1 after the 4H–SiC substrate is thinned down to 50 μm. The coefficient of thermal expansion (CTE) of the composite substrates can be engineered by changing the thickness of SiC substrate.