Enhanced deposition rate of diamond in atmospheric pressure plasma CVD: Effects of a secondary discharge

Diamond deposition in an atmospheric pressure direct current arcjet was enhanced through induced nonequilibrium chemistry. A secondary discharge was created in the thin boundary layer above the growth substrate by means of a positive potential applied to the growth surface (thus forming a strong electric field across the boundary layer). This applied electric field provides a targeted energy addition to the free electrons in the plasma, heating them above the bulk gas temperature (T-e>T-g). These energetic electrons are then able to promote electron impact dissociation of molecular species, specifically molecular hydrogen, to yield an enhanced flux of radicals important in the diamond growth process to the substrate surface. A factor of 7 increase in growth th rate was observed with 4.9 A/cm(2) and 170 V across the secondary discharge as compared with an unbiased (floating) substrate case. The enhanced growth rate observed with an active secondary discharge may be attributable to increased fluxes of atomic hydrogen and hydrocarbon radicals to the growth surface. Two-dimensional imaging of the plasma jet found a substantial increase in the H-alpha emission from the boundary layer with a positive potential applied, This result may indicate that the secondary discharge is in Fact increasing the electron temperature and atomic hydrogen concentration in the very near surface region as compared with the unbiased substrate case. SEM and Raman spectroscopy analysis indicated that uniform, high quality films were deposited in all cases reported here. (C) 1997 Elsevier Science S.A.