Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) study of SF₆ and SF₆–CF₄ plasma‐treated low‐density polyethylene films

Abstract

Timeof-flight secondary ion mass spectrometry (ToF-SIMS) is used to monitor in a semi-quantitative way the chemical modifications produced at low-density polyethylene (LDPE) film surfaces by SF, and SF,-CF, plasma treatments. The influence of the plasma treatment time (SF, plasma) and the gas composition (SF6-CF, plasma) have been investigated. The ToF-SIMS results are compared with plasma diagnostics (mass spectrometry and optical emission spectroscopy) and with some earlier XPS characterization.The ToF-SIMS study of SF, plasma-treated LDPE films as a function of the treatment time shows two different structural developments. Beside the expected formation of C,F, structures due to the grafting of F atoms, ToFSIMS detects the presence of SF, species at the surface. Their high sensitivity to ablation, due to the plasma ions, was related to two possible interactions of plasma species with the LDPE surface: an adsorption of SF:/-ions or a dissociative chemisorption of SF, neutral species. In the latter case, the low binding energy of the S-C bond can explain the high sensitivity to ablation.In the case of SF,-CF, plasma treatment, the incorporation of fluorine, as seen by ToF-SIMS, is a function of the gas composition. Two maxima are observed when the second gas (either SF, or CF,) is introduced at low concentration (-10%). These maxima are confirmed by XPS and actinometric results and are explained with respect to the reciprocal influence of both gases in the plasma discharge.

Static secondary ion mass spectrometry (S-SIMS) Part 2: material science applications

“…For instance, an SF 6 plasma converts progressively the surface methyl and methylene groups of a HC polymer into CF, CF 2 and CF 3 . This could be readily followed by looking at e.g., the C n F m ions or the F À signal (Van Ooij & Michael, 1988;Lyons et al, 1990;Khairallah et al, 1994;Le Âonard et al, 1995). Similar studies on PCA (Occhiello et al, 1989b;1989c) indicated the degradation of the aromatic ring as well as the¯uorination of the polymer.…”

Modes of rf capacitive discharge in low-pressure sulfur hexafluoride

“…Rf capacitive discharge in SF 6 is widely applied in technological processes of etching silicon-based materials [2,3], GaAs [4], treatment of polyethylene films [5] and textile [6], cleaning walls of technological vessels from etching or deposition products [7], etc. Therefore a large number of papers are devoted to studying rf discharge in SF 6 both in experiment and in theory.…”

Chemical Analysis of Plasma‐treated Organic Surfaces and Plasma Polymers by Secondary Ion Mass Spectrometry

“…The fluorination of low‐density polyethylene (LDPE) films by CF 4 plasmas (70 kHz and 13.6 MHz), and by SF 6 and SF 6 ‐CF 4 RF plasmas (13.6 MHz), was studied as a function of the frequency and electrode configuration in the first case, and as a function of the treatment time (up to 30s) and the proportions of the two gases in the reactor in the second case . After pure SF 6 plasma treatment, new F‐containing fragment ions appear in the positive ion mass spectra, essentially C x H y F + , C x F y + , and SF x + .…”

“…(a) Normalized ToF‐SIMS intensities of some fluorocarbon and fluorohydrocarbon ions for two SF 6 plasma treatment times (0.23 and 10 s); (b, c) Variation of the normalized ToF‐SIMS intensity of the CF + and F − ions as a function of the SF 6 percentage in the gas feed. Adapted from Léonard et al…”