Mechanisms of low temperature growth of diamond using halogenated precursor-gases

The addition of halogenated gases allows a significant lowering of the substrate temperature T-sub for diamond growth compared to the conventional system containing hydrogen and methane. We succeed in diamond film deposition at T-sub = 350 degrees C in HFCVD and MWCVD using CHF3, C2H5Cl and Cl-2. A further decrease of T-sub is possible on the expenses of the growth rate and the deposition time. The composition of the gas phase is analyzed using quadrupole mass spectroscopy (QMS) and optical emission spectroscopy (OES). Almost all chlorine from the precursor-gas reacts to HCl, resulting in a composition of pure hydrocarbons almost the same as that for the H-2/CH4 system. The quality of the deposited films is analyzed using Raman spectroscopy and the atomic composition of the films is detected by secondary ion mass spectroscopy (SIMS). A decrease of T-sub leads to a decrease of diamond film quality and growth rate. The SIMS measurements show at high deposition temperatures an almost complete lack of chlorine atoms in the films but a high concentration on the diamond surface. At deposition temperatures below 500 degrees C the chlorine concentration increases also in the bulk. The atomic concentration is in the range of 100 ppm. These data suggest that the halogens are involved in surface reactions. At high T-sub they desorb in the CVD growth process and cannot be detected in the film. If T-sub is lo lowered the desorption of the halogens is incomplete and chlorine is incorporated in the diamond film. We assume that the halogens make possible low temperature growth of diamond by surface reactions leading to the formation of active surface sites at which diamond growth species can be adsorbed. (C) 1998 Elsevier Science S.A.