Influence of nitrogen addition on oxyacetylene flame chemical vapor deposition of diamond as studied by solid state techniques and gas phase diagnostics

Abstract

The effect of nitrogen addition on oxyacetylene flame deposition of diamond has been investigated. Two-dimensional laser-induced fluorescence measurements of CN radical distributions in the flame during deposition have been performed. These measurements show that nitrogen added to the source gases and nitrogen from the ambient air dominate the CN formation in the central and outer-flame area, respectively. Both sources of nitrogen have a significant influence in the area between the other two. Most of the observed film morphologies, which were studied by scanning electron microscopy, can be understood from the recently developed deterioration-gradient (DG) model for chemical vapor deposition of diamond, reported by J. J. Schermer et al. [J. Cryst. Growth 243, 302 (2002)]. It was found that the nitrogen range in which the α-parameter, defined by C. Wild et al. [Diamond Relat. Mater. 2, 158 (1993)], changes from slightly below or equal to 1.5 to a value of 3 or more, is extremely narrow. This implies that under the present experimental conditions it is very hard or impossible to grow a layer with a central area consisting of 〈001〉 oriented {001} topped crystallites. Observed radial changes in the morphology of the sample grown without nitrogen addition were explained from radial changes in the gas phase composition, caused by interaction of the flame with nitrogen and, presumably, oxygen from the ambient air. The central growth rate as a function of the nitrogen flow shows an increase by more than a factor of 1.5 in going from 0 to 5 sccm and stays more or less constant between 5 and 25 sccm. From Raman spectra of the central area it clearly followed that under the present conditions even the smallest added nitrogen addition resulted in a decrease of the film quality. This may be related to a possible stimulation of the growth of non-diamond carbon compounds by nitrogen. A correlation, the origin of which is not known, was found between the stepwise narrowing of a broad band in the Raman spectra, which was attributed to non-diamond carbon, and changes in the morphology of the diamond films. Combining the present data with findings from literature, support is generated for the idea that CN is important in causing the effects of nitrogen on diamond growth.