EFFECT OF GAS-PHASE COMPOSITION ON THE SURFACE-MORPHOLOGY OF POLYCRYSTALLINE DIAMOND FILMS

The film morphology of polycrystalline diamond was observed under a wide variety of conditions by an advanced hot-filament chemical vapor deposition (AHFCVD) method. The main advantage of AHFCVD is the independent and accurate controllability of the chemical vapor deposition (CVD) parameters, especially of the substrate temperature. Clear faceted planes were obtained under the conditions of higher filament temperature (2000-2100 degrees C), pressures of 30-300 Torr, lower methane concentration (about 1.2% or less), lower gas flow rate (800 standard cm(3) min(-1) or less), shorter distance between the filament and substrate (10 mm or less), and lower substrate temperature (910 degrees C or less). At higher pressures of 200-300 Torr, the facets became (100) dominant. The development of (111) and (100) crystal habits was examined with respect to the concentration of the chemical species in the gas phase as estimated by numerical simulation. A key parameter governing the crystal habit was found to be the concentration ratio of H to CH3; the (111) face developed at higher [H]/[CH3], while the (100) face could dominantly develop at lower [H]/[CH3]. Both the (111) and (100) orientations of the films are then discussed in terms of the reconstruction of the growing surface and the contribution of this [H]/[CH3] ratio.