Sk. Baldwin et al., ENHANCED DEPOSITION RATE OF DIAMOND IN ATMOSPHERIC-PRESSURE PLASMA CVD - EFFECTS OF A SECONDARY DISCHARGE, DIAMOND AND RELATED MATERIALS, 6(2-4), 1997, pp. 202-206
Diamond deposition in an atmospheric pressure direct current arcjet wa
s enhanced through induced nonequilibrium chemistry. A secondary disch
arge 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 appli
ed electric field provides a targeted energy addition to the free elec
trons in the plasma, heating them above the bulk gas temperature (T-e>
T-g). These energetic electrons are then able to promote electron impa
ct 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 dis
charge as compared with an unbiased (floating) substrate case. The enh
anced growth rate observed with an active secondary discharge may be a
ttributable to increased fluxes of atomic hydrogen and hydrocarbon rad
icals to the growth surface. Two-dimensional imaging of the plasma jet
found a substantial increase in the H-alpha emission from the boundar
y layer with a positive potential applied, This result may indicate th
at the secondary discharge is in Fact increasing the electron temperat
ure and atomic hydrogen concentration in the very near surface region
as compared with the unbiased substrate case. SEM and Raman spectrosco
py analysis indicated that uniform, high quality films were deposited
in all cases reported here. (C) 1997 Elsevier Science S.A.