The Influence of Hollow Cathode Geometry and N2-H2 Gas Mixture on the 2 MHz RF-DC Plasma Species and Density

RF-DC plasma combined with the hollow cathode effect is used to generate plasma inside a hollow cavity. A high-density plasma was formed inside a vacuum chamber using a 2 MHz RF generator. A hollow cathode was utilized to focus the power at the voltage of 150 V with DC bias of -500 V. The plasma system was specially designed for titanium nitriding process at low temperature using N2-H2 gas mixture. The N2-H2 gas with a flow rate of 90-10 mL/minute was conducted at pressure 20 to 150 Pa. The cylindrical and rectangular hollow cathodes are used to make the discharge containing attractive atoms or molecules inside the hollow cavity. The trapped electrons could trigger the secondary electron emission that induced high-density plasma. The geometry components such as gap size, diameter, and cavity depth combined with variations of chamber pressure have been studied to produce high-density plasma. The species inside of N2-H2 plasma were detected by OES based on light emission. The high-intensity peaks of N2* molecules from the second positive system and N2+ ions from the first negative system at the wavelength range of 300 to 500 nm were detected to obtain effective plasma species for the nitriding process.