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 assisted chemical vapor deposition technique (MPCVD), the bias enhanced nucleation (BEN) stet) has been developed to avoid the scratching pretreatment and to palliate the low nucleation density of diamond crystals on the most common substrate used: pristine single silicon substrates. This treatment that occurs before the diamond growth step often consists in the application of a negative bias voltage of the substrate/ substrate holder system, which is electrically insulated from the reactor wall. in the case of the MPCVD process, this bias induces a complex superposition of two cold discharges: the microwave and the bias discharges. Unfortunately, this complex configuration leads to inhomogeneous deposits in terms of quality, nucleation rate, and thickness. Furthermore, the reproducibility of the BEN step is generally poor in terms of diamond deposits and electrical BEN parameters. In order to better understand and overcome this pretreatment step, we have studied the temporal and spatial evolution of the bias discharge according to diamond propagation tin terms of kinetic and geometrical effects) and its electron emission, the nature and the shape of the substrate holder tin terms of aging and point effects). We have shown that the presence of the bias plasma is necessary. Based on this observation, we propose a phenomenological mechanism to explain the heterogeneous deposit and the poor reproducibility. Our results with a MPCVD reactor confirm the proposed model and some experimental modifications allow us to obtain homogeneous diamond films elaborated with reproducible electrical parameters. This work would permit the synthesis of a large area of highly oriented films obtained by BEN on single silicon substrates. (C) 1998 American Institute of Physics. [S0021-8979(98)00616-1]