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 th ird 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 a mounts of oxygen, others investigated the influence of halogen,eases. Recently we demonstrated that the substrate temperature for diamond de position 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 sys tem [5]. In the present study we expanded our investigations to chlori nated precursor gases and the microwave plasma CVD process. Using C2H5 Cl as a precursor gas we succeeded in low-temperature growth of diamon d (LTGD) in both CVD systems but with CHF, the substrate temperature i n 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 m icrowave power or filament-temperature the atomic chlorine concentrati on is higher because of the low bonding energy of the HCl molecule. Us ing 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 p ossible in the C/H/Cl system as well as in the C/H/F system. Summarizi ng many different deposition experiments, we define a diamond growth a rea for a substrate temperature that is dependent on the concentration of radicals in the gas phase. (C) 1997 Elsevier Science S.A.