WORLDWIDE STATUS OF LOW-TEMPERATURE GROWTH OF DIAMOND

Recent trends in low temperature growth of diamond films (LTGD) are reviewed. LTGD can be classified into non-substrate-heating processes and substrate-heating processes. In non-substrate-heating processes, room temperature growth of diamond has been demonstrated by sputtering, r.f. plasma, and laser excitation methods. However, the film quality has still not been analyzed quantitatively. In substrate-heating processes, polycrystalline diamond growth has been confirmed at substrate temperatures between 80 and 135-degrees-C by microwave plasma of both CO-H-2 and CO-O2-H-2 systems, electron cyclotron resonance plasma of C2H5OH-(H-2, Ar, He) systems, and tantalum filament decomposition of the CH4-H-2 system. Source gases providing oxygen and excess atomic hydrogen in the gas phase were found to be suitable for LTGD because these species suppress the inclusion of amorphous components and the degradation of crystallinity which are likely to occur at low substrate temperature. The lowest substrate temperature for synthesis of diamond films with the same crystallinity as natural diamond is about 400-degrees-C. The film quality deteriorates near 130-degrees-C, which may be due to the incorporation of H, O, and OH from the gas phase into the diamond films. Growth rates are between 0.01 and 0.2 mum h-1 near 400-degrees-C, and 0.035 and 0.3 mum h-1 at 130-degrees-C. Growth rates can be accelerated by the addition of Ar or He to the source gas, but inert gases may cause the film quality to deteriorate.