Fieldmap of morphology of diamond films grown by use of d.c. plasma glow discharge chemical vapour deposition

Abstract

We have studied the morphology and texture of CVD diamond films grown by d.c. plasma glow discharge CVD by means of SEM analysis and X-ray diffraction. This works follows a preliminary work on morphology changes from disordered to textured structure with a thorough investigation in a wide interval of substrate temperature, 955–1150°C, and methane into hydrogen volume concentration, 0.9–3.8%. The other deposition parameters have been kept constant: overall pressure, 210 Torr, gas flow rate 300 sccm, power density, 38 W mm −2. Care has been taken to prepare the substrate with a standard procedure in order to avoid unreproducible effects on nucleation and growth. In-plane texture has been determined by calculating the average percentage of oriented grains from the area of the Bragg peaks and the powder diffraction data. The results of this quantitative analysis confirm the SEM morphology observation. A fieldmap has been developed for the film morphology and texture as functions of substrate temperature and methane concentration in order to give an useful information for directing the CVD process by means of this particular method. Moreover a qualitative agreement with previously reported data supports the hypothesis that the morphology does not depend on the particular CVD method but only on the deposition conditions, i.e. the deposition parameters and the activation of the reactant gases. The density of nucleation has been also studied by SEM analysis, leading to conclude that there is no competition between grains and evolutionary growth for the used deposition conditions, resulting in grain sizes within the same order of magnitude of the film thicknesses. A clear correlation has been found between the rate of growth of the films and their texture, in the sense that maxima and minima of the rate of growth always correspond to maxima in the diamond texture. A thorough explanation of this correlation will require further ad hoc investigations.