DIAMOND DEPOSITION BY CHEMICAL-VAPOR-DEPOSITION PROCESS - STUDY OF THE BIAS ENHANCED NUCLEATION STEP

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]