The chemistry of halogens on diamond: effects on growth and electron emission

Abstract

Diamond growth using halogenated precursors was studied in several diamond growth reactors. In a conventionao plasma reactor, diamond growth using the following gas mixtures was studied: CF{sub 4}/H{sub 2}, CH{sub 4}/H{sub 2}, CH{sub 3}F/H{sub 2}, and CH{sub 3}CL/H{sub 2}. Both the diamond growth measurements demonstrated ineffective transport of halogen radicals to the diamond surface during the growth process. In order to transport radical halogen species to the diamond surface during growth, a flow-tube reactor was constructed which minimized gas phase reactions. Also, the flow-tube reactor enabled pulsed gs transport to the diamond surface by fast-acting valves. Molecular beam mass spectroscopy was used to find condition which resulted in atomic hydrogen and/or atomic fluorine transport to the growing diamond surface. Although such conditions were found, they required very low pressures (0.5 Torr and below); these low pressures produce radical fluxes which are too low to sustain a reasonable diamond growth rate. The sequential reactor at Stanford was modified to add a halogen-growth step to the conventinoal atomic hydrogen/atomic carbon diamond growth cycle. Since the atomic fluorine, hydrogen and carbon environments are independent in the sequential reactor, the effect of fluorine on diamond growth could be studied independently of gas phase reactions. Although the diamond growth rate was increased by the use of fluorine, the film quality was seen to deteriorate as well as the substrate surface. Moreover, materials incompatibilities with fluorine significantly limited the use of fluorine in this reactor. A diamond growth model incorporating both gas phase and surface reactions was developed for the halocarbon system concurrent with the film growth efforts. In this report, we review the results of the growth experiments, the modeling, and additional experiments done to understand fluorine with diamond surfaces.