Diagnostics of N₂ dissociation in RF plasmas by vacuum ultraviolet emission and absorption spectroscopy

The N₂ dissociation degrees in a 50 MHz inductively coupled plasma (ICP) are evaluated by a procedure using vacuum ultraviolet optical emission spectroscopy (VUVOES). The number density of N ⁴S° atoms (n_N) is evaluated from the N₂ dissociation degree by determining the N₂ rotational temperature that is in equilibrium with the gas temperature. The n_N evaluated by VUVOES is crosschecked by the n_N measured by vacuum ultraviolet absorption spectroscopy (VUVAS). The comparison reveals a fair proportionality between the n _Ns evaluated by VUVOES and those measured by VUVAS, suggesting that VUVOES is applicable to the monitoring of N₂ dissociation in low-pressure, high-density N₂ plasmas. The number density of N ²D° metastables is also measured by VUVAS and found to be comparable to the number density of the ground-level N atoms ( ⁴S°). The dissociative recombination of with electrons is suggested as a possible mechanism of N ²D° metastable generation that makes the N ²D° density comparable to the N ⁴S° density in the pulsed N₂ ICP during power-off periods.