Fluorocarbon Thin Films Research Articles

Area-selective atomic layer deposition of Al2O3 using inkjet-printed inhibition patterns and lift-off process

Area-selective atomic layer deposition (AS-ALD) has been studied as an alternative method for metal oxide ALD film patterning in the microelectronics industry. To perform AS-ALD, area-deactivation or -activation processes should be implemented in advance using selective surface modification through a photography-based lift-off process and printing techniques. This study introduces a novel approach for Al2O3 AS-ALD using inkjet-printed inhibition patterns. ALD-inhibition patterns with two-layer structures of fluorocarbon (FC) thin film and photoresist (PR) were patterned by inkjet printing. Low surface energy FC thin films were used to block the Al2O3 nucleation and growth during the ALD process, and PR was patterned to easily remove ALD-inhibition patterns using a lift-off process. To demonstrate AS-ALD, an Al2O3 thin film approximately 10 nm thick was deposited via an in-house built system with a multiple-slit gas source. The proposed AS-ALD method was evaluated for topological analysis using atomic force microscopy and surface composition analysis using a time of flight secondary ion mass spectrometry after Al2O3 deposition and a lift-off process. Finally, a 6 nm thick Al2O3 film was selectively patterned by the lift-off process using an inkjet-printed 1.28 μm thick FC-covered PR inhibition pattern.

Gate‐Tunable Potential Barrier on Dual‐Gate Graphene Transistor with Fluorocarbon Thin Film

AbstractThis article reports on the charge transport characteristics across the potential barrier generated by a local dual‐gate modulation at the surface of p‐doped graphene via surface contact on a fluorocarbon (CF) thin film. Owing to simple physical contact, the strong electron affinity of the fluorine atoms in CF stably increases the hole density of graphene, which leads to a massive p‐doping effect in graphene. Then, potential barrier height can be generated and modulated across the channel by forming a local dual‐gate device structure. Different gate biases in dual‐gate operation can split electrical characteristics of a single graphene into highly conductive region and region of sparse charge density, creating large chemical potential difference at the boundary between the two which determines the value of barrier height. Moreover, the device characteristics follow a simple model of the metal–semiconductor junction well in addition to the effect of charge concentration discrepancy in graphene. These results reveal that it is possible to create an ideal and controllable potential barrier composed of a single material using the highly doped graphene with the local dual‐gate structure.

SURFACE PROPERTIES OF FLUOROCARBON COATINGS PRODUCED BY LOW-FREQUENCY PLASMATRON AT ATMOSPHERIC PRESSURE

This paper presents the results of studies conducted on coatings based on thin fluorocarbon films obtained by plasma-enhanced chemical vapor deposition using low-frequency plasmatron and low-temperature plasma at atmospheric pressure. The possibility of forming thin fluorocarbon layers by supplying a cyclohexane/carbon tetrafluoride gas mixture to substrates made of polymeric materials (polyethylene terephthalate and polystyrene) has been demonstrated and the main technological modes of deposition process have been established. The absorption spectra of the obtained coatings were studied, the influence of the gas discharge energy contribution on the concentration of fluorocarbon compounds was established, and the band gap was calculated using the Tauc method. The surface relief of the obtained structures was considered using atomic force microscopy and the root-mean-square deviation of the surface roughness was calculated, which reached a maximum of 36 ± 3 nm. Using the Oliver-Pharr method, the nanohardness and Young's modulus of elasticity of the obtained coatings were calculated, which amounted to 0.447 ± 0.025 and 6.10 ± 0.39 GPa, respectively.

Investigation of thermal property of plasma‐polymerized fluorocarbon thin films

AbstractThe physical property changes in the plasma‐polymerized fluorocarbon (PPFC) thin films near the melting temperature (Tm) were investigated through chemical structure analysis. The PPFC thin films, produced by semi‐crystalline polytetrafluoroethylene (PTFE)‐based polymer sputtering target, form amorphous polymers with outstanding properties, such as high water repellency and high optical transmittance, electrical insulation, and chemical resistance. Interestingly, in‐situ X‐ray photoelectron spectroscopy analysis revealed that the PPFC thin films maintained their physical properties at temperatures above the Tm in vacuum and exhibited properties similar to those of bulk PTFE while maintaining amorphous structure. Therefore, this thin film can be applied to various devices and surface coatings manufactured at high temperatures.

Bio-Inspired Hierarchical Micro/Nanostructured Surfaces for Superhydrophobic and Anti-Ice Applications.

We report a scalable and cost-effective fabrication approach for constructing bio-inspired micro/nanostructured surfaces. It involves silicon microstructure etching using a deep reactive ion etch (DRIE) method, nanowires deposition via glancing angle deposition (GLAD) process, and fluorocarbon thin film deposition. Compared with the smooth, microstructured, and nanostructured surfaces, the hierarchical micro/nanostructured surfaces obtained via this method showed the highest water contact angle of ∼161° and a low sliding angle of <10°. It also offered long ice delay times of 2313 s and 1658 s at −5°C and −10°C respectively, more than 10 times longer than smooth surfaces indicating excellent anti-icing properties and offering promising applications in low-temperature environments. These analyses further proved that the surface structures have a significant influence on surface wettability and anti-icing behavior. Hence, the GLAD process which is versatile and cost-effective offers the freedom of constructing nanostructures on top of microstructures to achieve the required objective in the fabrication of micro/nanostructured surfaces when compared to other fabrication techniques.

Facile fabrication of micro/nano-structured wrinkles by controlling elastic properties of polydimethylsiloxane substrates

Multiscale wrinkled structures are widely used in practical applications, such as smart adhesion, surface engineering, and stretchable electronics owing to their easy and low-cost strategy for controlling surface morphologies. This study demonstrates a facile technique for creating multiscale wrinkles of fluorocarbon thin films deposited on soft and stiff polydimethylsiloxane (PDMS) substrates by regulating the elastic properties of the substrates. The elastic properties of the substrates were changed by varying the crosslinking temperatures and the amount of crosslinking agent. The wrinkling structures were strongly influenced by the elastic properties of the substrate during a fluorocarbon polymer sputtering process. For the stiff PDMS substrates, wrinkles with periodic and sinusoidal patterns were observed due to the thermal compression of the bilayer system after deposition. Spontaneous hierarchical structures were generated on soft PDMS substrates by the penetration of fluorocarbon molecules into the PDMS substrates during the sputtering process.

Over 59 mV pH−1 Sensitivity with Fluorocarbon Thin Film via Fluorine Termination for pH Sensing Using Boron‐Doped Diamond Solution‐Gate Field‐Effect Transistors

pH sensing facilitates many substantial aspects of the society such as chemical laboratory analysis, agriculture, or water and soil qualities. However, existing pH sensors have problems and limitations such as fragility, hysteresis, or slow responding time. In this research, a new method utilizing fluorocarbon thin film via fluorine termination and boron‐doped diamond (BDD) solution‐gate field‐effect transistors (SGFETs) for pH sensing is developed for the first time. The fluorocarbon film device demonstrates a high pH sensitivity of 67.4 and 34.9 mV pH−1 in acid and alkaline pH regions, respectively.

Effects of carbon concentration on high-hardness plasma-polymer-fluorocarbon film deposited by mid-range frequency sputtering

We propose a method for fabricating high-hardness plasma-polymer-fluorocarbon (PPFC) thin films with controllable optical and surface properties via manipulation of the target composition design and sputtering power density. The carbon/polytetrafluoroethylene (PTFE) composite polymeric material targets with the low electrical resistance were prepared by press-molding using a mechanically mixed powder of PTFE, carbon nanotubes, and graphite. The composite targets showed electrical sheet resistances of 0.1–100 Ω/sq. PPFC thin films were deposited by mid-range frequency (MF) sputtering at power densities within 0.62~4.92 W/cm2. The maximum surface hardness of the PPFC thin film was 4.75 GPa, which was 21.6 times higher than that of fluorocarbon thin film sputtered from PTFE under the same conditions. With the increase of the carbon concentration in the target, the carbon cross-linking density of the PPFC thin film increased but the fluorine concentration decreased. The concentration of fluorine in the PPFC thin films grew with increasing sputtering power density. The MF sputtered carbon-rich PPFC thin films are controllable with physical properties of optical transmittance, surface hardness and surface water repellency which could be applied as protective layers for transparent flexible devices.

Investigation of Surface Properties of Fluorocarbon Films Produced Using Plasma Techniques.

Different fluorocarbon thin films were deposited on Si substrates using two different plasma polymerization methods. Fluorine-containing hydrophobic thin films were obtained using inductively coupled plasma (ICP) and capacitively coupled plasma (CCP) with a mixture of fluorocarbon precursors (C2F6, C3F8, or c-C4F8) and an unsaturated hydrocarbon (C2H2). Different process parameters for plasma polymerization (e.g., processing time) were used to generate various fluorocarbon thin films. The hydrophobic properties and mechanical properties of the new products were measured using a profilometer, water contact angle measurements, pencil hardness, and a 90° peel test. The chemical compositions of the fluorocarbon thin films were characterized using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). The water contact angle results showed that the ICP technique provides a more hydrophobic surface compared to the CCP technique. XPS and FT-IR analyses indicated that the ICP technique generated more fluorine-related functional groups (i.e., CF-CFn, CF2, and CF3) in the surface region, while the CCP technique produced fewer fluorine-containing functional groups. However, the fluorocarbon thin films produced using the CCP technique showed greater adhesive strength than did the fluorocarbon thin films produced using the ICP technique. These results are useful to establish the optimal condition for the fabrication of fluorocarbon films and to develop the device in bio-sensing applications.

Significantly Reduced Secondary-Electron-Yield of Aluminum Sheet with Fluorocarbon Coating

In this work, the surface of Al sheet was coated with a fluorocarbon (FC) thin film by radio frequency (RF) sputtering of polytetrafluoroethylene (PTFE) to investigate the influence of dielectric coatings on the secondary electron yield (SEY) behavior of Al sheets. Atomic-force microscopy (AFM) and energy-dispersive spectroscopy (EDS) were employed to identify the surface topographies and elemental contents of the samples with FC coatings. Water contact angle (WCA) measurements were performed to characterize the surface tension as well as the polar and dispersion components of the samples’ surface. The secondary electron- mission (SEE) behavior of the samples was determined by measuring the SEY coefficients in an ultra-high vacuum chamber with three electron guns. The experimental results indicated that the longer sputtering time effectively led to the increase in coating thickness and a higher ratio of F/C, as well as the continued decrease of surface tension. A quite thin FC coating of about 11.3 nm on Al sheet resulted in the value of maximum SEY (δmax) dropping from 3.02 to 1.85. The further increase in coating thickness beneficially decreased δmax down to 1.60, however, at the cost of a ten-fold thicker coating (ca. 113 nm). It is found that increasing the coating thickness contributes to reducing SEY coefficients as well as suppressing SEE. The results are expected to guide the design of dielectric-coating for SEY reduction as well as multipactor suppression on Al.

Self-Cleaning Transparent Heat Mirror with a Plasma Polymer Fluorocarbon Thin Film Fabricated by a Continuous Roll-to-Roll Sputtering Process.

This paper proposes a novel self-cleaning transparent heat mirror (SC-THM) produced by depositing a plasma polymer fluorocarbon thin film on a silver-and-SiN x multilayer structure fabricated by continuous roll-to-roll sputtering. The optimal structure and the thickness of each thin film of three-layer and five-layer SC-THMs were derived from optical simulation. In the five-layer SC-THM, the visible light transmittance was 60.67% at a wavelength of 406 nm and the infrared (IR) transmittance was 6.86% at a 1000 nm wavelength and 2.50% at a 1500 nm wavelength. The value of the performance parameter Tvis/ Tsol was 1.70. The SC-THM exhibited self-cleaning with a very good water repellency of more than 111°, achieved by applying a low-surface-energy fluorocarbon thin film to the top layer. This study successfully demonstrated the IR blocking properties of an SC-THM through IR reflection and IR irradiation experiments.

Combination of laser patterning and nano PTFE sputtering for the creation a super-hydrophobic surface on 304 stainless steel in medical applications

Subsequent host tissue responses to implanted biomaterials that occur immediately after implantation are highly determined by surface events between tissue-implant interfaces and in contact biological fluids. These events are directly affected by biomaterial surface features. The surface of the 304 stainless steel as a high used metallic biomaterials in blood contact medical devices need to hemocompatibility improvement. The hemocompatibility features of the surface are affected by various factors, including physical and chemical properties, particularly wettability. A high level of surface hydrophobicity helps to enhance the hemocompatibility. For this, many surface engineering techniques are used to modify and control surface wettability behavior that can be adapted to improve the hemocompatibility and overall performance of biomaterials.In the present study, a laser patterning model is applied for creation of parallel micro-grooves on the surface of 304 stainless steel in first stage. Secondly, a fluorocarbon thin film has been deposited on the inscribed surface of the steel using polytetrafluoroethylene (PTFE) sputtering. The results show that, by creating a micro-groove pattern on the steel surface, the wettability behavior of the surface will also change and the contact angle will be increased from 80° to almost 111°. Moreover, the deposition of a polymer thin film has led to a decrease in surface energy and, thereby, an increase in hydrophobicity and making a contact angle of 149°. From these finding, it can be concluded that, with simultaneous use of topography and surface chemistry changes, the wettability behavior of the surface has been increased and a high and appropriate level of hydrophobicity has been achieved consequently, that is suitable for hemocompatibilty of blood-contact devices.

Fluorocarbon Thin Films Fabricated using Carbon Nanotube/Polytetrafluoroethylene Composite Polymer Targets via Mid-Frequency Sputtering

Carbon nanotube/polytetrafluoroethylene composite polymer targets are proposed for use in the fabrication of fluorocarbon thin films using the mid-frequency sputtering process. Fluorocarbon thin films deposited using carbon nanotube/polytetrafluoroethylene composite targets exhibit an amorphous phase with a smooth surface and show a high water contact angle, optical transmittance, and surface hardness. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy studies reveal that as the carbon nanotube concentration increased in the composite target, a carbon cross-linked structure was formed, which enhanced the film hardness and the modulus of the fluorocarbon thin film. Large-area fluorocarbon thin films with a substrate width of 700 mm were successfully fabricated by a pilot-scale roll-to-roll sputtering system using a carbon nanotube/polytetrafluoroethylene composite target.

SiO2 etching in an Ar/c-C4F8/O2 dual frequency capacitively coupled plasma

SiO2 etching in an Ar/c-C4F8/O2 dual frequency (13.56 and 60 MHz) capacitively coupled plasma is examined in this paper. Experiments were done in a dilute mixture of c-C4F8/O2 in Ar for a wide range of conditions (low frequency power, c-C4F8 flow rate, O2 flow rate, total flow rate, and gas pressure), and the SiO2 etch rate was measured at multiple locations on 300 mm wafers. A two-dimensional hybrid fluid-kinetic plasma model was used to understand the experimental observations. A surface coverage based etch mechanism was found to best capture the experimental results over the range of conditions considered. In this mechanism, the SiO2 surface gets partially covered by a fluorocarbon thin film, and SiO2 is etched by energetic ions in the presence of these fluorocarbons. Conditions that enhance fluorocarbon coverage such as higher c-C4F8 flow rate or lower O2 flow rate lead to higher SiO2 etch rate. Many relevant quantities such as the fluxes of ions and neutral radicals to the wafer and ion energy sensitively depend on gas pressure. However, their effects on SiO2 etching were found to partially cancel each other, and the SiO2 etch rate exhibited only weak dependence on pressure. In order to capture experimentally observed uniformity trends, electron heating needed to be treated kinetically (using a Monte Carlo model) in the plasma model. The surface coverage based etch model is also compared to a thickness based dielectric etch mechanism, which is more applicable to fluorocarbon rich plasmas.

Plasma Processing with Fluorine Chemistry for Modification of Surfaces Wettability.

Using plasma in conjunction with fluorinated compounds is widely encountered in material processing. We discuss several plasma techniques for surface fluorination: deposition of fluorocarbon thin films either by magnetron sputtering of polytetrafluoroethylene targets, or by plasma-assisted chemical vapor deposition using tetrafluoroethane as a precursor, and modification of carbon nanowalls by plasma treatment in a sulphur hexafluoride environment. We showed that conformal fluorinated thin films can be obtained and, according to the initial surface properties, superhydrophobic surfaces can be achieved.

Wear Characteristics of Fluorocarbon Thin Films Deposited Using Inductively Coupled and Capacitively Coupled Plasma Methods

Wear Characteristics of Fluorocarbon Thin Films Deposited Using Inductively Coupled and Capacitively Coupled Plasma Methods

Characterizing fluorocarbon assisted atomic layer etching of Si using cyclic Ar/C4F8 and Ar/CHF3 plasma.

With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO2 and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C4F8 and CHF3) and synchronized, plasma-based Ar+ ion bombardment [D. Metzler et al., J. Vac. Sci. Technol., A 32, 020603 (2014) and D. Metzler et al., J. Vac. Sci. Technol., A 34, 01B101 (2016)]. For low energy Ar+ ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etch depth per cycle of SiO2 and Si but is limited with regard to control over material etching selectivity. Ion energy over the 20-30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF3 has a lower FC deposition yield for both SiO2 and Si and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F8. The thickness of deposited FC layers using CHF3 is found to be greater for Si than for SiO2. X-ray photoelectron spectroscopy was used to study surface chemistry. When thicker FC films of 11 Å are employed, strong changes of FC film chemistry during a cycle are seen whereas the chemical state of the substrate varies much less. On the other hand, for FC film deposition of 5 Å for each cycle, strong substrate surface chemical changes are seen during an etching cycle. The nature of this cyclic etching with periodic deposition of thin FC films differs significantly from conventional etching with steady-state FC layers since surface conditions change strongly throughout each cycle.

Superhydrophobic Paper by Facile and Fast Atmospheric Pressure Plasma Etching

Superhydrophobic and to some extent oleophobic paper surfaces are prepared using atmospheric pressure plasma etching. A novel dielectric barrier discharge operating in helium–oxygen mixture is used to rapidly etch organic material from paper surface and create hierarchical topography and subsequently a thin fluorocarbon film is deposited to modify the surface energy. The enhancement of surface topography is achieved via the selective removal of organic matter over inorganic calcium carbonate (calcite) fillers that co-exist in paper. The process led to the fabrication of roll-off superhydrophobic paper with water contact angles >150° and hysteresis <10° for all samples treated over 2 min with no deterioration of paper quality. Further treatment over 8 min resulted also in diiodomethane repellent surfaces.

22aPS-75 フルオロカーボン薄膜の電子状態に関する研究

22aPS-75 フルオロカーボン薄膜の電子状態に関する研究

Nanoscale Mechanical and Tribological Properties of Plasma Nanotextured COP Surfaces with Hydrophobic Coatings

Cyclo olefin polymer (COP) surfaces, treated in oxygen plasmas under highly anisotropic conditions to favor roughness formation, are coated with thin hydrophobic films to form surfaces of enhanced hydrophobicity. As hydrophobic coatings, plasma-deposited fluorocarbon or spin-coated Teflon thin films are implemented. Nanoindentation and nanoscratch experiments have been employed to elucidate the effect of plasma treatment on the mechanical and tribological performance of the synthesized materials. It is shown that short-time plasma treatment slightly changes mechanical and tribological properties of plasma-nanotextured COP, as compared to untreated. The plasma deposited hydrophobic film on the COP surfaces presents good adhesion and it effectively protects the surfaces, reducing plastic deformation.