Macromolecule formation in low density CF4 plasmas: The influence of H2

Abstract

High molecular weight fluorocarbon species are regarded as important contributors to the nucleation of films and particulates in fluorocarbon plasmas. The chemical reaction mechanisms by which fluorocarbon macromolecules form within a plasma are generally unknown. To elucidate these mechanisms, experiments were conducted in a rf capacitively coupled discharge in a Gaseous Electronics Conference reference cell. The relationships between macromolecule growth and plasma pressure, power, flow rate, and the fraction of H 2 in the CF 4 gas feed are identified. Macromolecule growth was found to increase with increased pressure and rf power, and decreased flow rate. A set of electron-induced dissociation and radical-recombination reactions are simulated using Chemkin-Aurora, a commercially available plasma chemistry model, and are in good agreement with the experimental results of macromolecule growth. We show that a primary mechanism by which fluorocarbon macromolecules form in a plasma occurs by electron-induced dissociation of a fluoroalkane to produce a fluoroalkyl radical and a fluorine atom, followed by a three-body radical-radical recombination reaction with CF 3 . Hydrogen is shown to have a profound effect on this reaction sequence by reducing the gas phase atomic fluorine concentration through the formation of HF which in turn increases the CF 3 concentration available to participate in the macromolecule growth process. At moderate levels of hydrogen in the feed gas (Ͻ20%), macromolecule growth is directly correlated with the fraction of hydrogen in the feed gas. At high concentrations of hydrogen, hydrofluorocarbon and hydrocarbon growth occurs in the plasma at the expense of fluorocarbon macromolecule growth. The conditions under which the formation of these species occurs is consistent with observations in the literature of dramatic reductions in silicon dioxide etching rate. The transition between the formation of fluorocarbon macromolecules and hydrocarbon species in a CF 4 /H 2 plasma is shown to be fundamental to understanding the growth process of each class of species within the plasma.

Comparative Study of the Superhydrophobic‐Modification of Silicone Rubber Surfaces by CF4 ICP and CCP

“…Figure 2 shows that the fluorine content introduced by CF 4 ICP is more than that introduced by CF 4 CCP at a fixed power of 200 W and the same treatment time, and both F contents obtained by the two processing techniques reach saturation when the treatment time is equal to or longer than 10 min. This corresponds to the results that CF 4 plasma fluorination and ablation or etching exist simultaneously and compete on the surface of the treated polymer, and this competition is closely related to the treatment power and time 19–21. Figure 3 shows that the ratio of [FC]/[FSi] for the SIR sample treated by CF 4 CCP is less than 0.25, and it decreases slightly with the increase of treatment time from 2 to 5 min, and then remains in the same state in spite of the increase of treatment time.…”

Fluorination of Boron-Doped Diamond Film Electrodes for Minimization of Perchlorate Formation

“…However, the BDDF-plasma electrode contained a mixture of CF (4.32%), CF 2 (2.81%), and –CF 3 (1.17%) groups (Figure S1b and Table ) which yielded a CF:CF 2 :CF 3 molar ratio of 3.7:2.4:1 (Table ). These results indicated that the attachment of free radicals (e.g., CF • , CF 2 • , CF 3 • , and F • ) occurred during the CF 4 plasma treatment. , The BDDF-PFOA electrode showed 15.2% surficial oxygen content, which may have formed during the synthesis process (i.e., electrochemical oxidation of formic acid and water) and indicates the surface was not completely fluorinated . The CF:CF 2 :CF 3 ratio for the BDDF-PFOA electrode was 0:2.6:1 (Table ).…”

Analysis and Modeling of Gas‐Phase Processes in a CHF3/Ar Discharge

“…All other rates were orders of magnitude lower and not of relevance for the plasma chemical model. Rates of fragmentation by binary electron collisions with other molecules were calculated by applying the electron density to the formulas for the rates given in the literature,11, 42 using an average mean electron energy of $\langle \varepsilon \rangle = 5.9\;{\rm eV}$ . The simulated densities of CF and CF 2 , based on these process rates and the reaction data in Table 1–3, were $n_{{\rm CF}} = 3 \times 10^{12} \,{\rm cm}^{{-} {\rm 3}} $ and $n_{{\rm CF}_{{\rm 2}} } = 1 \times 10^{13} \,{\rm cm}^{{-} {\rm 3}} $ during the plasma glow (converged data, 10th simulated plasma pulse).…”