An optical emission spectroscopy study of the plasma generated in the DC HF CVD nucleation of diamond

Optical emission spectroscopy (OES) was used to study the plasma generated by the activation of the gas phase CH₄ + H₂ both by hot filaments and by a plasma discharge (DC HF CVD) during the nucleation of CVD diamond. The effects of nucleation parameters, such as methane concentration and extraction potential, on the plasma chemistry near the surface were investigated. The density of the diamond nucleation and the quality of the diamond films were studied by scanning electron microscopy (SEM) and Raman scattering, respectively. The OES results showed that the methane concentration influenced strongly the intensity ratio of H_β-H_α implying an increase of electron mean energy, as well as CH, CH⁺, C₂. A correlation between the relative increase of CH⁺ and the diamond nucleation density was found, conversely the increase of C₂ contributed to the introduction of defects in the diamond nuclei.