Effect of oxygen on the bias-enhanced nucleation of diamond on silicon

The influence of traces of oxygen in the process gas on the bias-enhanced nucleation (BEN) of diamond on silicon has been studied in the present work. CO2 in concentrations ranging from 0 to 3000 ppm was added during the nucleation procedure at U-bias = -200 V in microwave plasma chemical vapour deposition (MPCVD). A significant influence of CO2 could already be detected for a concentration of 75 ppm, corresponding to a C:O ratio of 600:1. It resulted in a continuous reduction of the biasing current and a delay in the nucleation process accompanied by a decrease of the final diamond-covered substrate surface area with increasing CO2 concentration. At 3000 ppm, the nucleation was completely suppressed. An etching of diamond nuclei by the oxygen could be excluded from in-situ growth rate measurements under bias. Instead, optical emission spectra of the IIB Balmer line indicated a decrease in electrical field strength in the plasma above the substrate. For all gas compositions allowing diamond nucleation, epitaxially aligned films could be obtained, provided that the duration of the biasing step was chosen appropriately. Thus, traces of oxygen do not completely suppress epitaxy. However, the in-plane orientation of the films as determined by X-ray diffraction measurements deteriorates with increasing oxygen concentration. (C) 1999 Elsevier Science S.A. All rights reserved.