The use of “actinometer” gases in optical diagnostics of plasma etching mixtures: SF6-O2

The spectroscopic emission intensities from excited F atoms in SF₆-O₂ discharges at 1 torr have been correlated to the densities of atoms in their ground electronic state by measuring the excitation efficiencies of the electrons in the energy range 11 to 17 eV with a method which essentially consists in the analysis of the emission of Ar or N₂, added as actinometer gases to the discharge mixtures. The general applicability of the method has been tested by a direct titration of F atoms with chlorine. The spectroscopic analysis has allowed the determination of useful information on the trends of both the electron densities and their energies as a function of the oxygen percent in the feed.     

Mechanism of silicon film deposition in the RF plasma reduction of silicon tetrachloride

Plasma-chemical reduction of SiCl₄ in mixtures with H₂ and Ar has been studied by optical emission spectroscopy (OES) and laser interferometry techniques. It has been found that the Ar:H₂ ratio strongly affects the plasma composition as well as the deposition (r _D) and etch (r _E) rates of Si: H, Cl films and that the electron impact dissociation is the most important channel for the production of SiCl_x species, which are the precursors of the film growth. Chemisorption of SiCl_x and the reactive surface reaction SiCl_x+H–SiCl_(x–1)0+HCl are important steps in the deposition process. The suggested deposition model givesr _D [SiCl_x][H], in agreement with the experimental data. Etching of Si: H, Cl films occurs at high Ar: H₂ ratio when Cl atoms in the gas phase become appreciable and increases with increasing Cl concentration. The etch rate is controlled by the Cl atom chemisorption step.     

Studies of R.F. discharges at moderate pressures and chemical applications—II. Nitrogen-hydrogen,nitrogen-methane and nitrogen-methane-hydrogen mixtures

Simultaneous vibro-rotational analyses have been carried out for the second positive system (SPS) of N₂ (C³П_u ? B³П_g), for the violet system (VS) of CN (B²Σ ? X²Σ) and for the Swan system (SS) of C₂ (d³П_g ? a³П_u), emitted by 35 MHz electrical discharges, containing N₂, H₂ and CH₄ flowing mixture s, in the 5–40 torr pressure range and at 1–10 Wcm^-3 power densities. The results are consistent with a Boltzman distribution for the rotational levels, but they show a deviation from this law for upper vibrational levels of CN and C₂.     

Spectroscopic diagnostics of R.F. discharges at moderate pressure and chemical applications—I. Pure nitrogen

A vibro-rotational analysis has been performed of the second positive system (SPS) of N₂ and of the first negative system (FNS) of N⁺₂ emitted by 35 MHz discharges in flowing nitrogen operated at pressures of 5–50 torr and power densities of the order of 1–10 W-cm^-3. The distributions of the vibrational and of the rotational levels follow Boltzmann's law in both the SPS and the FNS with T_v = 4000°K and T_R = 2800°K for the N₂(C³Π_u) state and T_v = 5100°K and T_R = 5800°K for the N⁺₂(B²Σ⁺_g) state and independent of pressure. Kinetic gas temperatures are between 1200 and 2000°K and increase with pressure; electron temperatures are in the range 15,000–9,500°K. The reversal of line intensities of the SPS and of the FNS observed with increasing pressure has been tentatively interpreted. Possible chemical implications of these results have been examined.     

Spectroscopic measurements of non-equilibrium nitrogen plasmas at moderate pressures

A local vibro-rotational analysis of the excited species, produced in a 35 MHz discharge reactor in flowing nitrogen, has been carried out by measuring radial and axial emission intensities of some vibrational sequences and selected rotational lines of the (0,2) band of the second positive system (SPS) of N₂ (C³Π_u - B³Π_g), in the pressure range 5–35 torr.Radial from lateral band or line emission intensities have been obtained by applying Abel's inversion technique to derive the corresponding vibrational and rotational temperatures with the use of Boltzmann plots. General maps of emission intensities and of vibrational and rotational temperature distributions within the reactor have been drawn.It is shown that a decrease of a factor 10³ in the emission intensities from the core to the periphery of the discharge corresponds to a variation in T_V and T_R of only a factor ?2. This result has been interpreted on the basis of the kinetic mechanisms for the excitation and deexcitation of chemical species under discharge conditions. The decrease of _V and the increase of T_R with increasing pressure are interpreted according to V-R (vibration-rotation) energy-transfer mechanisms.     

Chemical mechanisms in C3F8-H2 radiofrequency discharges

Discharges fed with C₃F₈-H₂ mixtures have been studied by means of mass spectrometry in a tubular reactor operated at 0.5 torr and 50 W. Comparison of the results with those obtained with emission actinometry give additional evidence that emission actinometry and mass spectrometry are powerful diagnostic tools to monitor stable and unstable species in discharges utilized for dry etching and polymer depositions. Mechanisms for end product formation and polymer deposition are also discussed.     

On the use of actinometric emission spectroscopy in SF6-O2 radiofrequency discharges: Theoretical and experimental analysis

A comparison of the results obtained by solving the Boltzmann equation with the experimental results from optical emissions obtained in SF₆-O₂ radiofrequency discharges, when N₂, Ar, and He are also admitted as actinometers, has allowed us to explore the potentialities and limits of actinometry. The use of different actinometers also allowed us to monitor the evolution of the electron distribution functions as a function of the plasma parameters.     

The Decomposition of Methane,Ethane, Ethylene and n-Butane in Electrical Discharges of Moderate Pressures

The decomposition of CH₄, C₂H₆, C₂H₄, and n-C₄H₁₀ has been investigated in radiofrequency plasmas operated at power levels of 1–8 cal cm^?3 sec^?1, 10–40 torr and flow rates of the hydrocarbons between 2 and 20 1 (STP) min^?1. It is shown that values of the rate constants are very close for all the hydrocarbons investigated and several orders of magnitude greater than those observed in their pyrolisis at comparable gas temperatures. Energy yields up to 30% can be observed for all hydrocarbons. It is suggested that the rate determining step for the decomposition process of all hydrocarbons investigated involves the rupture of a C-H bond in vibrotationally excited molecules.     

Optical emission spectroscopy and actinometry in CCl4-Cl2 radiofrequency discharges

Radiofrequency discharges fed with CCl₄-Cl₂ mixtures have been studied in the pressure range 0.3 to 0.6 torr by means of emission spectroscopic actinometry with Ar, He, and N₂ as actinometers. Two different reactors, a parallel plate and a capacitively coupled tubular one, have been utilized for this study to obtain information for a large range of electron energy distributions. Analysis of the experimental results demonstrates the following: the utilization of actinometry and its range of validity, the importance of electron attachment to CCl_x species during the plasma decomposition process, and the effects of the presence of chlorine and “glowpolymer” in the discharge medium.