We propose a new method using a spiral shape nitrogen plasma with a long magnetic connection length to produce high density nitrogen (N) atoms for nitriding application. A high density N molecular ion plasma was generated by DC discharge and is transported along a long spiral magnetic field line. As a result, the electron temperature drops along the magnetic field to be low enough to produce dissociate recombining plasma, where dissociative recombination would occur to generate N atoms. 2D Langmuir probe measurement showed that the electron temperature and density decreased along the magnetic field. Optical emission spectroscopy showed the ratio of the atomic N and N molecular emission intensities increased with a discharge power. The ground state N atom density was estimated by analyzing the atomic line intensity.
Nitrogen (N) atomic density is measured by an actinometry method in the toroidal shaped plasma device NAGDIS-T, where the plasma produced in a DC arc discharge is cooled as spiraling down inside the vacuum vessel. The plasma was characterized with an electrostatic probe, and we applied the actinometry method to obtain the N density using the deduced electron density and temperature. The actinometry method used the Ar line emissions at 750.4 or 811.5 nm and N emission at 746.8 nm. The measured N densities from the actinometry was compared with that from the vacuum ultraviolet absorption spectroscopy.
For the development of a high nitrogen atom density source, we produced nitrogen plasmas and measured the nitrogen atom density using vacuum ultraviolet absorption spectroscopy (VUVAS) at high neutral gas pressure (>1.5 mTorr) and discharge power (>500 W) in the NAGDIS-T, which could generate spiral-shaped dissociative recombining plasmas. It was seen that the nitrogen atom density increases with increasing neutral gas pressure and discharge power, and it reached 6.2 × 10 17 m −3 . In the low gas pressure case, the estimated atom density was confirmed to be consistent with that measured by the actinometry method.
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