The effect of mixed electric field on characteristic of Ar–N₂ plasma jets for TiN surface treatment

In this paper, we present a new structure for Ar–N₂ plasma jet generation where a pulsed electric field is modified with a second alternating electric field, referred to as mixed electric field. The electric field distribution through the jet tube is simulated for the conventional and newly designed plasma jet. It is demonstrated that the value of the electric field becomes stronger due to mixed electric field, particularly between the tip and ring electrodes through the tube. Not only does the length of plasma jet increase from 15 cm to 30 cm when a mixed electric field is employed, but also the temperature of the substrate surface decreases from 62 °C to 52 °C at the same power, which is favorable for industrial applications. It is shown that introducing more nitrogen into the plasma jet shortens the length of the jet, while the jet length could substantially be improved using the current design. The capability of surface treatment at different electrical power is also evaluated on deposited TiN layers by the conventional and current plasma jet. The surface treatment by the newly designed plasma jet based on mixed electric field shows no detectable damage on the TiN layer, while the conventional plasma jet degrades the surface at equal power. The hydrophilicity of the surface is also measured by the contact angle of a water droplet, which decreases from 66 to 31° after surface treatment, implying the surface becomes more hydrophilic. The temperature distribution on the substrate is also evaluated for Ar–N₂ plasma jet and compared with the conventional plasma jet structure. (paper)