S. Barrat et al., DIAMOND DEPOSITION BY CHEMICAL-VAPOR-DEPOSITION PROCESS - STUDY OF THE BIAS ENHANCED NUCLEATION STEP, Journal of applied physics, 84(4), 1998, pp. 1870-1880
In the case of diamond films synthesized by the microwave plasma assis
ted chemical vapor deposition technique (MPCVD), the bias enhanced nuc
leation (BEN) stet) has been developed to avoid the scratching pretrea
tment and to palliate the low nucleation density of diamond crystals o
n the most common substrate used: pristine single silicon substrates.
This treatment that occurs before the diamond growth step often consis
ts in the application of a negative bias voltage of the substrate/ sub
strate holder system, which is electrically insulated from the reactor
wall. in the case of the MPCVD process, this bias induces a complex s
uperposition of two cold discharges: the microwave and the bias discha
rges. Unfortunately, this complex configuration leads to inhomogeneous
deposits in terms of quality, nucleation rate, and thickness. Further
more, the reproducibility of the BEN step is generally poor in terms o
f diamond deposits and electrical BEN parameters. In order to better u
nderstand and overcome this pretreatment step, we have studied the tem
poral and spatial evolution of the bias discharge according to diamond
propagation tin terms of kinetic and geometrical effects) and its ele
ctron emission, the nature and the shape of the substrate holder tin t
erms of aging and point effects). We have shown that the presence of t
he bias plasma is necessary. Based on this observation, we propose a p
henomenological mechanism to explain the heterogeneous deposit and the
poor reproducibility. Our results with a MPCVD reactor confirm the pr
oposed model and some experimental modifications allow us to obtain ho
mogeneous diamond films elaborated with reproducible electrical parame
ters. This work would permit the synthesis of a large area of highly o
riented films obtained by BEN on single silicon substrates. (C) 1998 A
merican Institute of Physics. [S0021-8979(98)00616-1]