A cylindrical inductively coupled plasma source (ICPS) is optimized for nitrogen atom production. How to operate in the bright mode (H-mode) in pure nitrogen at relatively low applied power is explained. Actinometry is developed for a quantitative determination of the nitrogen dissociation fraction in the ICPS. These results are compared with those obtained outside the ICPS by modulated beam mass spectrometry. A qualitative agreement is obtained between the nitrogen dissociative fraction inside and outside the ICPS. The higher magnitude of the dissociation fraction given by mass spectrometry compared with that derived from actinometry is explained by the contribution of dissociative recombination of near the exit hole of the ICPS. A dissociation fraction of up to 0.7 is observed by mass spectrometry. Some results are also reported for argon–nitrogen gas mixtures.

http://iopscience.iop.org/article/10.1088/0022-3727/38/24/003/pdf

Nitrogen dissociation in a low pressure cylindrical ICP discharge studied by actinometry and mass spectrometry

Electron-impact excitation of $\mathrm{Ar}\mathrm{}\mathrm{I}$ from the ground ${3p}^{6}{}^{1}{S}_{0}$ as well as the two metastable levels of the ${3p}^{5}4s$ ${(}^{3}{P}_{2}$ and ${}^{3}{P}_{0})$ configuration to all ten levels of the ${3p}^{5}4p$ excited configuration are calculated in the distorted-wave approximation. Polarization of the ground state is explicitly included by adding a polarization potential in the calculation. Unitarization of the scattering matrix $\mathbf{S}$ is carried out by including the elastic terms, and effects of unitarization in the $\mathrm{LS}$ as well as $\mathrm{jj}$ formalisms are investigated. The excitation cross sections are calculated from threshold to $\ensuremath{\sim}100$ eV. The calculations are compared and contrasted with recent experimental data and other theoretical work. The study shows that the effect of the polarization potential is not very significant but unitarization of the $\mathbf{S}$ matrix reduces the cross sections considerably and the cross sections obtained using the two different methods of unitarization are significantly different for some excitation transitions. The results are useful for analyzing low-pressure plasmas used in processing applications as well as electron beam excitation, as in excimer lasers.

Electron-impact excitation from the ground and the metastable levels of Ar I

A method and apparatus for adapting the nature of an ion beam during processing of the surface of a solid workpiece so as to improve the reduction of surface roughness (smoothing) by using a GCIB. In addition, the invention provides for surface smoothing in combination with etching to predetermined depths and surface contamination removal. Advantages are minimum required processing time, minimum remaining roughness of the final surface, and reduction in the amount of material that must be removed in order to attain a desired level of smoothness.

Adaptive GCIB for smoothing surfaces

N2?x% Ar plasma gas mixture, generated in a hollow cathode RF discharge system, has been characterized by both optical emission spectroscopy (OES) and double Langmuir probe, as a function of experimental parameters: total pressure (5?33?Pa), and different fractions of argon (7 ? x ? 80), at a constant applied RF power of 300?W. N2 dissociation degree has been investigated qualitatively by both the actinometry method and the ratio of the atomic nitrogen line emission intensity at 672.3?nm to the vibrational band (0?0) of the N2 second positive system at 337.1?nm. Both methods showed that the increase in argon fraction enhances the dissociation of N2, with a maximum at x = 50 for the pressure of 5?Pa, although the two methods give two opposite trends as a function of total pressure. Spectroscopic measurements showed that the vibrational temperature of the N2 second positive system increases with both argon fraction and total pressure increase, it lies between 4900 and 12?300?K. Langmuir probe measurements showed that, in the remote zone, the electron temperature falls in the range 1.57?1.75?eV, the density varies between 5 ? 109 and 1.4 ? 1010?cm?3 and that both the plasma ionization degree and electron temperature increase towards the source. In addition, the process of plasma?polyamide (PA) surface interaction, in the remote plasma zone, has been studied through OES analysis during plasma treatment of PA to monitor the possible emissions due to the polymer etching. An increase in atomic nitrogen line (672.3?nm) intensity is obtained, atomic carbon line (833.52?nm) and the band emission (0?0) from the CN (B?2?+?X?2?+) violet system were observed. The PA surface modification has been confirmed through the improvement of its hydrophilic character as the water contact angle measured after the plasma treatment significantly decreased.

https://iopscience.iop.org/article/10.1088/0022-3727/41/4/045205/pdf

Diagnostics of N2–Ar plasma mixture excited in a 13.56 MHz hollow cathode discharge system: application to remote plasma treatment of polyamide surface

Enhancement of the molecular nitrogen dissociation and ionization levels by argon mixture in flue nitrogen plasma

The key technical challenge in the molecular beam epitaxial (MBE) growth of group III nitrides is the lack of a suitable source of incorporatable nitrogen. In contrast with the growth of the other III–V compound semiconductors by MBE, direct reaction of N2 with excess group III metal is not feasible, because of the high bond strength of dinitrogen. An incorporatable MBE nitrogen source must excite N2 forming a beam of atomic nitrogen, active nitrogen (N2*), or nitrogen ions. rf and electron cyclotron resonance sources use electron impact excitation to obtain atomic nitrogen and in the process generate a wide variety of excited ions and neutrals. Experiments have shown that ionic species in the beam degrade the morphology of the epitaxial layer and generate electrically active defects. Recent theoretical studies have predicted that ground state atomic nitrogen will successfully incorporate into the growing GaN surface, while atomic nitrogen in either of the excited doublet states will lead to etching. In this article, we report on the development of an ultrahigh vacuum-compatible arcjet source which uses an electric arc to thermally dissociate N2. The thermal excitation mechanism offers selective excitation of nitrogen and control of kinetic energy of the active species. This source has been fabricated from refractory materials and uses two stages of differential pumping to minimize the pressure in the growth chamber. The arcjet has been reliably operated at power levels of 10–300 W, with no visible degradation of the thoriated tungsten cathode after 300 h. No metal contaminant lines can be found in the optical emission spectrum. Using an Ar-seeded beam for calibration of the optical spectrum, we find that the arcjet plasma is far from local thermodynamic equilibrium, and show that the fraction of atomic nitrogen in the beam ranges from 0.3% to 9%. This corresponds to a flux of 0.1–4 monolayers per second at the MBE sample location. With an articulated Langmuir probe sampling the beam at the MBE growth position, we find a positive ion flux of less than 4× 10−9 A/cm2, a maximum ion kinetic energy of 3.5 eV, a median electron energy of 1 eV, and a maximum electron energy of less than 4 eV. With increasing arcjet power, the ion and electron fluxes increase and the ion energy distribution shifts to lower energies. No change in the electron spectrum is observed. Quadrupole mass spectra of the ion flux measured on the arcjet axis show that the N+/N2+ ratio has a maximum at an arcjet power of about 35 W.

Ultrahigh vacuum arcjet nitrogen source for selected energy epitaxy of group iii nitrides by molecular beam epitaxy

One of the fundamental requirements for reliable critical dimension measurement with a scanning probe microscope is stability of the stylus against flexing and against erosion. We report on the wear of an etched optical fiber when scanned across a variety of surfaces. The optical fiber probe tip was used in a novel scanning probe microscope employing a balance beam force sensor.

Stability of glass probe tips for critical dimension measurement

A UHV-compatible nitrogen arcjet suitable for the growth of III-nitrides by molecular beam epitaxy is described and characterized. The arcjet operates at powers between 10W and 300W (the highest power used for these studies); typical nitrogen flows range between 5sccm and 100sccm. Optical emission spectra show the presence of activated atomic (N*) and molecular (N2*) nitrogen. A collisional radiative equilibrium model has been employed to provide insight into the excitation state of the active nitrogen. These results indicate that the arcjet is capable of supplying atomic nitrogen fluxes consistent with growth rates on the order of several monolayers per second. Langmuir probe measurements conducted near the position of the sample holder in the MBE chamber show the charged particle flux density is very low. The arcjet operates over a large powerpressure parameter space, and properties of the arc can be systematically “tuned” to provide a source suitable for selected-energy-epitaxy.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400217284

Design and Characterization of a UHV Arcjet Nitrogen Source

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Ultrahigh vacuum arcjet nitrogen source for selected energy epitaxy of group iii nitrides by molecular beam epitaxy

Stability of glass probe tips for critical dimension measurement

Design and Characterization of a UHV Arcjet Nitrogen Source