Diamond Thin Film Deposition and Interface Microstructure.

Diamond films were deposited on scratched silicon substrates by microwave plasma assisted chemical vapor deposition (MPACVD). A continuous film was formed after two hours deposition at processing conditions of 900 ^circC, 50 torr, 1% methane in hydrogen balance, and flow rate 200 sccm. The diamond/silicon interface was studied by transmission electron microscopy (TEM). Two types of interfaces were identified: Type A interfaces contain an amorphous transition layer composed of silicon, carbon, and oxygen; the diamond overgrowth on this layer consists of nanocrystalline grains with random orientations. Type B interfaces consist of large diamond grains having special orientations with respect to the silicon substrate, without an obvious presence of a glassy phase and with a much lower oxygen content than type A interfaces. The special orientations of diamond grains on silicon were identified as (i) <110> 90 degree rotation, (ii) <110> 60 degree rotation, and (iii) diamond {111 } plane tilted 6 degree from silicon {220} plane. These orientation relationships are analyzed in terms of geometric models that seek the best fit between the diamond and silicon lattices at the interface plane. Misfit dislocation, which accommodates the mismatch between film and substrate, is analyzed and found to create small deviation of diamond grain from the above exact orientations. The bonding of the diamond/silicon interface is examined by electron energy loss spectroscopy (EELS). The result shows concentrated sp^2 carbon bonding on the interface. The transition from silicon lattice to diamond lattice is studied through ball-and-stick models. The five- and seven-member rings on the interface serve to reduce strain and accommodate extra carbon atoms on the diamond side.