A study of the factors influencing the morphology of diamond thin films grown via hot filament chemical vapor deposition

In this study the morphology of hot filament chemical vapor deposited diamond films as a function of growth parameters was investigated. Morphological studies are needed for a complete understanding of growth mechanisms responsible for diamond growth, which is still in the stages of development. These studies are needed in order to make the important connection between the extreme properties and various applications of CVD diamond films. The effects of filament material, substrate temperature, methane concentration and addition of nitrogen to the input gas mixture were investigated. The films were deposited in a hot filament reactor and characterized using scanning electron microscopy. Atomic force microscopy was used to quantitatively analyze some of the growth features. High index planes, belonging to the {221} and {331} family of planes, were found to comprise a hopper shaped {111} "face", which is observed within a narrow range of growth parameters. Rhenium, tungsten and tantalum filaments were used to investigate the possible effect of filament material on morphology. It was found that the contamination levels from the filament varied dramatically even when the filaments were used under identical conditions. Quantitative determination of the metal content in the films was carried out by neutron activation analysis. The filament material did not appear to affect the morphology or the growth rate of the growing film. Diamond crystals with octahedral, cubo-octahedral and cube geometry were grown by various combinations of growth parameters. A morphology map was generated for the reactor using different concentrations of methane (0.5-1.5 %) and varying the substrate temperature (536-1140 °C). Such maps have been generated for microwave plasma enhanced CVD before and are very useful In controlling film morphology and thereby film properties. It was found that the growth rates In the various crystallographic directions differ In their dependence on the growth parameters, which supports the arguments that growth on different faces takes place by different mechanisms. Baseline morphology maps become essential If the effect of another parameter Is to be studied. The effect of addition of nitrogen was studied by the addition of ammonia to the Input gas mixture. The addition of nitrogen (N/C -1/6) showed a dramatic effect on the crystal morphology. The extent of the effect was found to depend on the region of morphology map that was being studied. Addition of ammonia was found to Increase the overall growth rate and decrease the growth rate ratio. The Increase In the growth rate was much higher In the [111] direction than In the [100] direction. These morphological studies are Important not only for understanding the mechanisms Involved In growth but also for realizing the full extent of the properties of CVD diamond for various applications.