Silicon substrate preparation for epitaxial diamond crystals

Using the microwave plasma-assisted chemical-vapour deposition technique (MPCVD), we study the role of the (100) silicon substrate preparation prior to the ultra short bias enhanced nucleation (USBEN) step via various pre-treatments. We study the effect of the silicon HF cleaning coupled with the hydrogen plasma exposure in order to determine the efficiency of these pre-treatments to eliminate the native oxide layer on the silicon surface prior to the bias step. We show that the residual oxygen content in the gas phase during the hydrogen plasma exposure can strongly affect the nucleation density because of the formation of an oxide layer which is detrimental for the synthesis of highly oriented diamond (HOD) films. Moreover, we study the effect of the carburation step, often used for the synthesis of HOD films and show that it raises the percentage of epitaxial crystals and the crystal density. Thus, we show that the achievement of high epitaxial crystal density is not only due to the BEN parameters but also to the silicon substrate preparation. As a conclusion, it appears that the silicon substrate preparation prior to BEN is fundamental for controlling the quality of epitaxial diamond films. (C) 2001 Elsevier Science B.V. All rights reserved.