Synthesis of uniform and large-area polycrystalline diamond films using microwave plasma chemical vapor deposition system

This study deals with the syntheses of polycrystalline diamond films on 4-inch-diameter (100 mm) silicon wafers using the microwave plasma chemical vapor deposition (MPCVD) system. The wafer was pretreated by the diamond powder nucleation method prior to deposition. Typical deposition conditions were as follows: CH4/ H-2, 4.5/300 sccm; discharge pressure, 25 Torr; deposition temperature, similar to 830 degrees C; and deposition time, 3, 6 or 9 h. The difference in surface roughness and thickness between the center and the edge of the polycrystalline diamond film was slightly increased as the deposition time increased. This phenomenon was also confirmed by Raman spectroscopy. The difference in surface roughness ranged from 2 to 5 nm. On the other hand, the difference in diamond film thickness ranged from 0.15 to 0.3 mu m. The oxygen (O) signal was observed in the spectra of all of the as-deposited diamond films. As the deposition time increased, the intensity of the oxygen (O) signal of diamond films decreased. It is suggested that the adsorption of oxygen and/or oxidation occurred primarily in diamond grain boundaries during the deposition of diamond films. It was found that uniform and good quality polycrystalline diamond films with reasonable deposition rates were successfully synthesized on 4-inch-diameter silicon wafers.