Monitoring of hydrocarbon concentrations in dust-producing RF plasmas

Abstract

In Ar and He radio-frequency (RF) plasmas with admixtures of C 2 H 2 and CH 4 the hydrocarbon chemistry has been studied in relation to dust particle formation by means of infrared tunable diode laser absorption spectroscopy (TDLAS) combined with Fourier transform infrared (FTIR) spectroscopy. The experiments were performed in a RF capacitively coupled parallel plate reactor at a frequency of f = 13.56 MHz, a pressure of p = 0.1 mbar and a flow rate of = 8 sccm of Ar or He with admixtures of 0.5 sccm C 2 H 2 or 1 sccm CH 4 . The power was P = 15 W. Using TDLAS, the temporal evolution of the concentrations of the methyl radical and of four stable molecules, C 2 H 2 , CH 4 , C 2 H 4 and CO, was monitored in the plasma. Simultaneously, the growth process of the dust particles was analysed by FTIR spectroscopy. The degree of dissociation of the acetylene precursor was found to be nearly constant in the range of 96% under stabilized conditions for both the Ar and He plasmas. In contrast, the degree of dissociation of the methane precursor varied between 45% and 90% depending (i) on the appearance of dust particles in the reactor volume and (ii) on the Ar or He plasma conditions. The methyl radical concentration was found to be in the range of 10 11 molecules cm −3 . The concentrations of all hydrocarbon species were strongly correlated with the dynamic of the dust formation. Fragmentation efficiencies of acetylene (R F (C 2 H 2 ) = 3.2 × 10 16 molecules J −1 ) and of methane (R F (CH 4 ) = (0.16-2.5) × 10 16 molecules J −1 ) and conversion efficiencies to the produced hydrocarbons (R C = (0.23-8.5) × 10 14 molecules J −1 ) could be estimated in dependence on the discharge conditions in the RF plasma.

Spectroscopic Investigations of Plasma Nitriding and Nitrocarburizing Processes Using an Active Screen: A Comparative Plasma Chemical Study of Two Reactor Types

“…The calculated values are normalized on the total www.cpp-journal.org plasma power. The fragmentation efficiency, R F , of the precursor, given in units of molecules J −1 , is expressed analogous to [24,25]:…”

Discharge dynamics, plasma kinetics and gas flow effect in argon–acetylene discharges

“…In particular, molecular growth and nanoparticle formation in acetylene and argon/acetylene RF discharges is receiving a constant attention, since more than two decades [1], [17], [18]. Concentrating on argon-acetylene CCRF plasmas, extensive experimental studies have been carried out to (i) investigate the space-time distributions of dust formation in the continuous or the pulsed regimes by laser light scattering and absorption [19], [20], (ii) thoroughly analyze the space-time evolution of both particle size and density by combination of Kinetic Mie ellipsometry and laser extinction [21], (iii) monitor hydrocarbon concentrations and analyze the chemical kinetics and the discharge dynamics by mass spectrometry and Tunable diode Laser Absorption spectroscopy [22], [23], [24], [25], (iv) investigate the initial clustering processes that induce particle nucleation by mass and molecular beam spectrometry [26] [27], (v) analyze the anion dynamics in the early stage of the discharge [28], (vi) study the particle cloud dynamics and its coupling with the discharge characteristics [29], [28], [30] and (vii) shed light on the role of argon metastables that turns out to be a key-species as far discharge dynamics and plasma kinetics are concerned [31], [32]. Besides these studies that were specifically dedicated to heterogeneous gas phase kinetics and plasma dynamics in Ar-C 2 H 2 CCRF discharges, an experimental effort was also devoted to the investigation of the interaction of the plasma species and the growing deposit.…”

Nanoparticle forming reactive plasmas: a multidiagnostic approach

“…Especially self-excited electron resonance spectroscopy (SEERS) [189], Mie elliposmetry [122,173,174], a laser fan for light scattering [101,103,116], 132 CHAPTER 5. SUMMARY AND OUTLOOK infrared absorption spectroscopy [190,191], and near-edge x-ray absorption fine structure (NEXAFS) [123] are promising candidates. Another important improvement of the 'Pequod'-reactor would be the development of a suitable control program.…”