Nitrogen dissociation degree in the diffusion region of a helicon plasma source obtained by atomic lines to molecular band intensities ratio

Abstract

Estimates of the dissociation degree in the diffusion region of a nitrogen helicon plasma source based on optical emission spectroscopy and Langmuir probe measurements are presented. The estimation procedure relies on measurements of the ratios of the intensities of the atomic triplet 3pS04→3sP4 (742.36, 744.23, and 746.83nm) to the intensity of the 4-2 band of the first positive system (AΣu+3→BΠg3) at 750.39nm and the measured relative vibrational distribution of the BΠg3 state. The electron energy distribution function, obtained from the second derivative of the Langmuir probe characteristic, and published excitation cross sections are used to calculate the electron-impact excitation rate coefficients—which are then compared to the atomic line and molecular band intensities to calculate the dissociation degree. For two distinct operating regimes, capacitively and inductively coupled, dissociation fractions of 5% and 13% are obtained in the expansion region of a 10mTorr, 500W, 10.74MHz helicon generated nitrogen plasma. The dissociation degree results suggest that the helicon source can provide excited molecular species for plasma assisted molecular beam epitaxy of III-group nitrides.

Atomic nitrogen source for the formation of aluminum nitride tunnel barrier SIS junctions

“…The dissociation rate of nitrogen molecules can be defined as D ¼ ½N=2½N 2 , where ½N and ½N 2 are the number densities of N and N 2 in the plasma. Several studies have demonstrated both theoretically and experimentally that the intensity ratio of atomic and molecular nitrogen emission correlates well with D [8][9][10]. However, in our case the N lines are not spectrally resolved and they are superimposed onto the molecular bands, as shown in Fig.…”

Optical Spectroscopic Analysis of ICP Nitridation for SIS Junctions With AlN Barriers

“…I N/N 2 are the measured intensities of the spectral emissions from excited N and N 2 respectively, and n N/N 2 are their corresponding densities [2], [6], [7]. Our trilayer deposition system, discussed in detail elsewhere [1], [8], was equipped with an Ocean Optics USB4000 Spectrometer and a 1 inch diameter collimating lens to record optical emissions from a nitrogen ICP.…”

“…To determine the relative amount of dissociated nitrogen in the plasma, we made the assumption that the observed plasma spectrum is mainly a superposition of the diatomic N 2 spectrum and discrete spectral lines associated with atomic N. For the spectrum of diatomic N 2 , we focus our attention to the well-studied B 3 Π g − A 3 Σ u first positive system, which is the most prominent diatomic band with high intensity spectra appearing from 478 to 2531 nm [10]. For the spectrum of atomic nitrogen, we focus on the 3p 4 S 0 → 3s 4 P nitrogen atomic triplet, as it lies within the range of optical emission captured by our spectrometer, overlapping spectra from the B 3 Π g − A 3 Σ u system, and is one of brightest emissions from atomic N in plasmas [7]. To extract the separate N and N 2 spectra, a similar approach to the one used by Endo [2] is implemented and described below.…”

Spectral intensity of the N2emission in argon low-pressure arc discharges for lighting purposes

“…For the electron collisions (1)-(8) impact cross sections σ (E) are used ( [33][34][35]; for (7), (8) shifted according to threshold energies) which are convolved with a Maxwellian EEDF, whereas processes (1)-(3) are evaluated by detailed balancing.…”