Cubic boron nitride film deposition and process diagnostics in a supersonic plasma jet chemical vapor deposition system with substrate bias

An examination of a supersonic plasma jet chemical vapor deposition system has been conducted with focus on its use for cubic boron nitride film deposition. To deposit cubic boron nitride thin films an argon---nitrogen plasma was generated in a converging diverging nozzle where these gases were accelerated to supersonic speeds, boron trifluoride and hydrogen were injected through the expanding portion of the torch nozzle, and the reactants were quickly quenched on the substrate to form a film. The deposition was enhanced by applying a bipolar pulsed bias to the substrate.; Plasma parameters believed important for cubic boron nitride deposition in this system including the plasma potential, electron temperature, gas temperature, ion density, and ion flux were examined using an electrostatic probe and optical emission spectroscopy. It was found that the ion flux to the substrate, a critical parameter in cubic boron nitride deposition, scales well with the ion density immediately in front of the substrate and throughout the plasma jet as affected by deposition conditions such as positive substrate bias current, torch discharge power, and reactant addition. The ion flux to the substrate was also enhanced by increasing the substrate bias pulse frequency, negative bias voltage, and negative duty cycle.; The cubic boron nitride content in the deposited films scaled well with parameters that increased the ion flux to the substrate. A deposition time of fifteen minutes was observed to favor cubic boron nitride deposition over a deposition time of ten minutes, likely due to the necessity of the deposition of a nucleation layer. Scanning electron microscopy of boron nitride films revealed that films composed of a predominately hexagonal phase appeared to be etched more than those exhibiting a predominately cubic phase, likely due to the preferential etching of hexagonal boron nitride by atomic fluorine in the plasma. The ratio of boron trifluoride to hydrogen reactant flow was found to be crucial towards our ability to deposit a boron nitride film, also likely due to the preferential etching of hexagonal boron nitride by atomic fluorine, the concentration of which is controlled by atomic hydrogen.