The 8-inch free-standing CVD diamond wafer fabricated by DC-PACVD

We report the fabrication of the 8-inch free-standing CVD diamond wafers by DC-PACVD process with the diode-type electrode configuration. Methane–hydrogen gas mixture was used as the precursor gas. The methane volume % in hydrogen, the gas flow rate and the chamber pressure were 5∼12%, 400 sccm and 100∼130 Torr, respectively. The discharge voltage and the discharge current were 840 ∼ 910 V and 90∼110 A, respectively. The substrate temperature was 1200∼1300 °C. The thermal conductivity, crystallinity and microstructure were characterized by the converging thermal wave technique, Raman spectroscopy, optical microscopy and SEM, respectively. The maximum growth rate was 9 μm/h for thermal grade 8-inch wafer. The deviation of thickness and the thermal conductivity over the 8-inch wafer was around 10% of the respective averaged values. The distribution of FWHM of Raman diamond peak over the wafer surface also showed excellent uniformity. The extremely simple scale-up of the present deposition technology was demonstrated.