Plasma Nitriding and Carbon Assisted Plasma Nitriding of Tantalum*

Plasma nitriding and carbon assisted plasma nitriding of tantalum were carried out. The nitride layer prepared with pure N₂ is composed of TaN and Ta₂N with hexagonal structure and a nitriding depth of 500 nm. The carbon assisted plasma nitriding process was carried out with the addition of methane into N₂ gas (5% and 10% in volume ratio) as carbon source. The carbonitride films were found to be composed of a larger number of micro-crystals nearly 1 um in size, with a uniform and compact surface, as revealed by scanning electron microscopy (SEM). TaC_1-xN_x with a face-centered-cubic (FCC) and Ta₂C_1-xN_x with hexagonal structure were identified by X-ray diffraction(XRD). The auger electron spectroscopy (AES) depth profiles reveal that the diffusion depth of nitrogen increased from 500 nm in nitride film to 1.5-3 μm in carbonitride films. The high solubility of nitrogen in tantalum carbide might be the main cause that promoted the diffusion of nitrogen during the plasma carbonitriding process.