Investigations concerning the role of fluorine and chlorine in the low temperature growth of diamond

The low-temperature growth of diamond (LTGD)is possible by adding a third element to the conventional system containing carbon and hydrogen, which does not allow diamond deposition below a substrate temperature of 550 degrees C. Some groups have reported on the addition of high amounts of oxygen, others investigated the influence of halogen,eases. Recently we demonstrated that the substrate temperature for diamond deposition in a hot-filament CVD process could be lowered to 400 degrees C using H-2/CHF3 gas mixtures instead of the conventional H-2/CH4 system [5]. In the present study we expanded our investigations to chlorinated precursor gases and the microwave plasma CVD process. Using C2H5Cl as a precursor gas we succeeded in low-temperature growth of diamond (LTGD) in both CVD systems but with CHF, the substrate temperature in MWCVD could not be lowered. We show that the concentration of atomic radicals like F. Cl and H is a very important parameter for LTGD. The advantage of using chlorine compared to fluorine is that with equal microwave power or filament-temperature the atomic chlorine concentration is higher because of the low bonding energy of the HCl molecule. Using CHF3, CFx radicals, detected by OES, are responsible for fluorine transport to the substrate. Because of the higher activation energy in the C/H/F system we did not succeed in LTGD in the MWCVD process, but using HFCVD and short distances from substrate to filament LTGD, is possible in the C/H/Cl system as well as in the C/H/F system. Summarizing many different deposition experiments, we define a diamond growth area for a substrate temperature that is dependent on the concentration of radicals in the gas phase. (C) 1997 Elsevier Science S.A.