Determination of the degree of dissociation in an inductively coupled hydrogen plasma using optical emission spectroscopy and laser diagnostics

Abstract

The knowledge of absolute concentrations of radicals in molecular discharges, such as the density of atomic hydrogen in H 2 plasmas, is crucial for understanding processes at the surface and is, therefore, of great interest in a variety of plasma applications. Reliable spectroscopic methods are indispensable for the determination of the degree of dissociation in processing plasmas. In this paper, we describe a novel optical emission spectroscopy method called two-gas actinometry (TGA). It is based on using a second actinometer gas to take into account dissociative excitation, which is of particular importance at comparatively low degrees of dissociation. TGA is employed for measuring the characteristic dependence of the degree of dissociation, in a wide range of plasma parameters, in an inductively coupled radio-frequency hydrogen plasma. Absolute densities with high accuracy are obtained using two-photon absorption laser-induced fluorescence spectroscopy.

Validating optical emission spectroscopy as a diagnostic of microwave activated CH4/Ar/H2 plasmas used for diamond chemical vapor deposition

“…The principles underpinning actinometry and its use as a plasma diagnostic have been thoroughly described elsewhere. 4,5,[22][23][24][25] Briefly, the method involves the addition of a small, known, amount of an inert tracer species ͑e.g., Ar, as here͒-the actinometer-to the gaseous medium of interest. Then, by comparing the intensities of specific emissions of the actinometer and of the species ͑X͒ of interest, the concentration of the latter can be deduced from the relation ͓X͔/͓act͔ = kI X /I act , ͑1͒…”

Understanding CO2 decomposition in microwave plasma by means of optical diagnostics

“…In order to measure the conversion of CO 2 , the so‐called optical actinometry method was applied. The principles of this method and its use for plasma diagnostics have been thoroughly described elsewhere . This method has been successfully applied for different gas mixtures containing molecules like N 2 , O 2 , H 2 , and CO 2 .…”

Investigation of InP etching mechanisms in a Cl2/H2 inductively coupled plasma by optical emission spectroscopy

“…However, this technique relies on many assumptions to be discussed, which is not the case for more direct spectroscopic techniques such as absorption spectroscopy 10 or laser induced fluorescence ͑LIF͒. 11 We will thus discuss the two main conditions that have to be fulfilled for actinometry to remain valid: ͑i͒ the production of excited species X ‫ء‬ ͑H ‫ء‬ , or Cl ‫ء‬ ͒ by electronimpact dissociative excitation of the parent molecule ͑H 2 , or Cl 2 ͒ must be negligible compared to the production of X ‫ء‬ by direct excitation of X, and ͑ii͒ the variation of the electronimpact direct excitation cross section for the species X ͑H or Cl͒ should follow that of the electron-impact direct excitation of the actinometer ͑Ar͒, so that the ratio of the excitation rate constants k directexc X / k directexc Ar remains unchanged in the range of plasma parameters explored. This second point is particularly important if the electronic temperature T e ͑or the electron energy distribution function͒ varies in the experiments.…”