Investigations on nitrogen addition in the CH 4–H 2 gas mixture used for diamond deposition for a better understanding and the optimisation of the synthesis process

Abstract

In this study, we report on some investigations on the effects of nitrogen addition in the conventional CH 4H 2 gas mixture employed for diamond synthesis by microwave plasma assisted chemical vapour deposition process. Diamond films have been achieved for CH 4 concentrations ranging between 0.5 and 3%, and nitrogen amounts introduced in the feed gas between 0 and 3000 ppm, for an averaged power density of 15 W cm −3. The analysis of the deposited films has been carried out using SEM, micro-Raman spectroscopy, profilometry, XRD and electrical characterisations. For the experimental conditions employed we have pointed out that the main and conjugated effects of nitrogen are to enhance the secondary germination formation and the {100} faces development. Consequently, these effects widely depend on CH 4 and N 2 concentrations and the use of an optimal gas mixture composition leads to a maximal growth rate, chemical purity and surface electrical resistance, with a {100}〈100〉 surface global morphology. Furthermore, the achievement of thicker diamond films using the optimal gas composition has permitted to confirm few mechanisms forecasted for thin films. In particular, these mechanisms are related to the {100}〈100〉 morphology formation and to the influence of nitrogen atom incorporation in the films on the surface electrical properties. Finally, the interest of nitrogen addition has been discussed in terms of process optimisation for the production of good quality diamond films for specific applications.