Deposition of Highly Ordered CF₂-Rich Films Using Continuous Wave and Pulsed Hexafluoropropylene Oxide Plasmas

Abstract

The structure and composition of fluorocarbon materials deposited in pulsed and continuous wave (CW) hexafluoropropylene oxide (HFPO) plasmas were investigated. Results indicate substantial dependence on substrate position relative to the rf coil. When the substrate was placed 8 cm downstream from the rf coil (25 W CW), highly amorphous, cross-linked films were obtained. In contrast, materials deposited 28 cm downstream from the rf coil contained less cross-linked moieties and a higher degree of order. Angle-resolved X-ray photoelectron spectroscopy (XPS) C 1s analysis showed that the 28 cm materials contain up to ∼80% CF 2 and CF 3 surface-enriched layers. Static secondary ion mass spectroscopy (SIMS) data revealed that these fluorocarbon materials are composed of long CF 2 chains. Near edge X-ray absorption fine structure (NEXAFS) analysis showed that the CF 2 chains were oriented perpendicular to the substrate surface for the films deposited at 28 cm downstream, while the films obtained 8 cm downstream do not exhibit any particular orientation. The compositions of materials deposited in pulsed HFPO systems have rf power and distance dependencies similar to those observed in the CW plasmas.

On the importance of ions and ion-molecule reactions to plasma-surface interface reactions

“…Over the past 5 years, we have studied a variety of fluorocarbon systems, including C 2 F 6 , C 2 F 6 /H 2 , CHF 3 [45], hexafluoropropylene oxide (HFPO) [46], C 6 F 6 , and 1,2,4-C 6 H 3 F 3 plasmas [47]. Most recently, we have focused on C 3 F 8 and C 4 F 8 plasmas as these systems are finding increased use in the microelectronics industry because of their lower global warming potentials [48].…”

“…Under the same deposition conditions, films formed in C 3 F 8 plasmas are less cross-linked (defined as %CF ϩ %C-CF x ϩ %C-H), with higher CF 2 content and F/C ratios than those deposited in C 4 F 8 plasmas. We have also found that films deposited even further downstream (i.e., 28 cm from the glow) have significantly lower cross-linking as do films deposited at lower applied rf powers [22,46].…”

Development of nano-structured icephobic surfaces based on plasma polymerization /

“…These results demonstrated that the increase in the distance between substrate and inlet gas leads to an increase in the hydrophobicity of a surface. Butoi et al [91] studied the effect of distance from a RF coil on the structure of a plasma polymerized Hexafluoropropylene oxide film. Their results showed that at a short distance, a cross-linked and amorphous film was obtained, while at a greater distance a linear and higher degree of order film was obtained.…”

“…Therefore, the absence of charged particles leads to orientation of the chains and networks of a coating characterized by a low surface energy [73]. Butoi et al [91] have also found that depositions performed at the farthest distance from the plasma glow discharge of Hexafluoropropylene oxide (HFPO) displayed a high degree of orientation. They showed that the free movement of undesired energetic species bombardment occurs simply at high distance because these species are lost through plasma recombination processes prior to reaching a substrate.…”

Mass Spectrometric Characterization of Pulsed Inductively Coupled Plasmas for Deposition of Thin Polyethylene Glycol-like Polymer Films.

“…Recently, several groups have demonstrated that increased chemical character of the desired polymer functional group is retained if the if plasma source is pulsed at frequencies in the hertz to kilohertz range. [7,8,9] Models have predicted that pulsing the discharge may be a unique means to controlling the kinetic processes in the plasma. [ 10] However, the mechanisms that lead to the plasma deposition of high quality functional polymers are still poorly understood.…”