Heteroepitaxial nucleation of diamond by bias pretreatment in an electron cyclotron resonance microwave chemical vapor deposition system

Abstract

Bias-enhanced nucleation (BEN) pretreatment was used for the nucleation of diamond particles on β-silicon carbide substrates in an electron cyclotron resonance (ECR) microwave chemical vapor deposition (CVD) system. Consequently, experimental conditions enabled the pretreatment of large-area substrates. After BEN and diamond growth, the density of diamond particles was strongly dependent on the BEN pretreatment parameters, such as the negative bias voltage, the total pressure, the duration of pretreatment and the methane concentration. Moreover, under appropriate BEN conditions, heteroepitaxial nucleation of the diamond particles was obtained and the proportion of particles oriented with the single-crystal substrates was also determined as a function of the BEN conditions. The maximum rate of oriented diamond particles was around 30% and typical particle densities were in the range 5 × 10 7 cm −2 to 5 × 10 8 cm −2. Heteroepitaxial nucleation was also obtained on substrates over a 40 mm length. For pressures increasing from 13 Pa (0.3 Torr) to 270 Pa (2.0 Torr), the maximum rate of oriented particles was obtained with an optimum bias voltage increasing from −30 V to −90 V. Epitaxial nucleation of diamond could then be strongly dependent on the energy distribution of positive ions involved in the BEN process. Although particle densities and rates of oriented particles deteriorated with the decrease in the substrate temperature from 900 °C to 500 °C, temperatures around 400 °C were suitable for obtaining particle densities close to those obtained at high temperatures.