CF4 Plasma Treatment Research Articles

Impact of CF4 plasma treatment on threshold voltage and mobility in Al2O3/InAlN/GaN MOSHEMTs

The shift of the threshold voltage Vth in Al2O3/InAlN/GaN metal–oxide–semiconductor high-electron-mobility transistors (MOSHEMTs) is demonstrated by CF4 plasma treatments. The accompanying channel mobility degradation is monitored to understand the tradeoff design space. The effective negative charge introduced by the F plasma treatments at the oxide interface is found to be as high as −0.73 × 1013 cm−2 (mobility > 500 cm2 V−1 s−1), sufficient to fully compensate for the net polarization charge in Al0.15GaN/GaN HEMTs. Although it is difficult to obtain Vth ≫ 0 V owing to the high polarization charges in InAlN, these MOSHEMTs with 1 µm gates show very low leakage (∼1 × 10−11 A/mm), low hysteresis, and low dispersion.

Eco-friendly step-and-flash imprint lithography using ultraviolet-curing liquid material with lactulose derivative derived from medicinal drugs for biomicrochips

Eco-friendly step-and-flash imprint lithography was investigated for the future high-volume manufacture of biomicrochips. A nanoimprinted ultraviolet-curing liquid material with a lactulose derivative derived from medicinal drugs was found to have excellent UV curing properties, film shrinkage during a UV curing reaction, and good etch selectivity with a silicon-based middle layer in CF4 plasma treatment. 80 nm half-pitch lines of the nanoimprinted ultraviolet-curing liquid material with a lactulose derivative were resolved using the process conditions for a trilayer including a silicon-based middle layer with a high silicon concentration of 21.5 wt % and a novolac-based bottom layer on a 100 mm silicon wafer in step-and-flash imprint lithography.

Graphene Grown on Ion-Implanted 4H-SiC and an Effect of Pre-Plasma Treatment

ABSTRACT4H-SiC substrates were annealed at 1500 °C for 30 min in 0.01 MPa Ar gas flow to make a graphene film. To clarify the effect of Al ion implantation and pre-plasma treatment, the graphene was fabricated on four different kinds of SiC substrates: without plasma treatment, with plasma treatment, Al ion-implanted without plasma treatment and Al ion-implanted with plasma treatment. The graphene films were analyzed by AFM and Raman spectroscopy. The Al ion implanted sample, which was then processed by CF4 plasma, showed small surface roughness of 3.49 nm (RMS), while the sample without CF4 plasma treatment showed large surface roughness of 8.41nm. Similar results were also observed for SiC samples without Al ion implantation. In Raman spectra, strong D-band, G-band and 2D-band signals were detected on both ion-implanted samples after annealing at 1500 °C, but weak D-band were observed on both samples without Al ion implantation. Raman mapping (2D-FWHM) showed that the graphene on ion-implanted SiC treated with CF4 plasma was more homogeneous than the one without CF4 plasma treatment. Hall measurements for SiC without Al ion implantation showed that graphene on SiC treated with CF4 plasma has higher mobility (389 cm2/Vs) than that without plasma treatment (136 cm2/Vs). Additionally, p-type graphene can be fabricated on Al ion-implanted SiC by CF4 plasma treatment.

Resistive Switching Characteristics of a SiOx Layer with CF4 Plasma Treatment

A 20 nm SiOx layer is deposited using radio‐frequency sputtering to form the resistive switching layer of a Cu/SiOx/Pt memory device. The SiOx‐based device demonstrates the resistive switching characteristics with an electrochemical reaction. CF4 plasma treatment was used to modify the SiOx layer and incorporate fluorine atoms into the SiOx layer. The bombardment damage and fluorine incorporation caused the SiOx film to form a stack‐like structure. This reduced the operating voltage and improved switching dispersion. The fluorine repaired the Cu/SiOx interface, thus increasing the barrier height of the Cu/SiOx interface and the resistance of the high resistance state. A statistical analysis of the conducting filament formation was performed in order to evaluate the number of formation/rupture sites. The resistive switching of the CF4‐treated sample had higher possibility to use the same filament sites; thus, the CF4‐treated sample had stable resistive switching behavior.

Multi-analyte biosensors on a CF4 plasma treated Nb2O5-based membrane with an extended gate field effect transistor structure

Multianalyte biosensors were fabricated with an Nb2O5 pH-sensitive membrane on silicon substrate in an EGFET structure. Incorporation of CF4 plasma treatment with an appropriate time of 15s was found to improve material properties and enhance performance. Multiple material analyses including XRD, AFM and SIMS indicate that CF4 plasma treatment reduces dangling bonds and passivates defects by forming strong bonds. Results indicate that an Nb2O5-based EGFET exhibited good performance with a high degree of sensitivity, a low hysteresis voltage and a low drift rate. Overall sensing performance for various ions of Na+, K+, urea and glucose detection was also enhanced. Our research indicates that Nb2O5-based biosensors with CF4 treatment show promise for future industrial biosensing applications.

Performance improvements of the hydrophobic and the dielectric properties of parylene C

The increase in the hydrophobicity at the same time as the reduction in the dielectric properties of an insulating material are the main factors necessary to improve the signal response of the electrowetting-on-dielectric and the organic field effect transistor electronic devices. Oxygen (O2) and fluorine (CF4) plasma treatments on 3.7 μm thicknesses-parylene C were carried out to understand the surface hydrophobicity character and their effect on the dielectric properties of the material. Fast hydrophobic recovery was observable during the first day after the O2 treatment due to the reorientation of the polar polymer end chains to the bulk of parylene C. CF4 plasma treatments reveal a noticeably increase of the hydrophobicity as the treatment time increases. Energy dispersive X-ray and Fourier transform infrared analyses have confirmed an increase in the number of fluorine containing CFx bonds where 1 ≤ x ≤ 3 after fluorine plasma treatments and after aging. The PPX C film treated with CF4 plasma at 500 W for 30 min indicated the best hydrophobic character and the best dielectric properties due to the highest loading fluorine content in our experimental conditions.

Damaged silicon contact layer removal using atomic layer etching for deep-nanoscale semiconductor devices

Silicon atomic layer etching (ALET) using Cl2 is applied to remove the damaged layer on a 30 nm contact silicon surface formed by high-energy reactive ions during high aspect ratio contact etching, and its effects on the damage removal characteristics are investigated. Compared to a conventional damage removal method, such as the low-power CF4 plasma treatment technique, ALET produces less secondary damage to the substrate and gives exact etch depth control and extremely high etch selectivity to the contact SiO2 insulating pattern mold. When ALET is applied after a conventional damage removal technique, the sheet resistance of the damaged contact silicon surface is improved to a level close to that of a clean silicon surface, while exact atomic-scale depth control is maintained without changes in the pattern mold profile.

One‐Step Formation of a Single Atomic‐Layer Transistor by the Selective Fluorination of a Graphene Film

In this study, the scalable and one-step fabrication of single atomic-layer transistors is demonstrated by the selective fluorination of graphene using a low-damage CF4 plasma treatment, where the generated F-radicals preferentially fluorinated the graphene at low temperature (<200 °C) while defect formation was suppressed by screening out the effect of ion damage. The chemical structure of the C-F bonds is well correlated with their optical and electrical properties in fluorinated graphene, as determined by X-ray photoelectron spectroscopy, Raman spectroscopy, and optical and electrical characterizations. The electrical conductivity of the resultant fluorinated graphene (F-graphene) was demonstrated to be in the range between 1.6 kΩ/sq and 1 MΩ/sq by adjusting the stoichiometric ratio of C/F in the range between 27.4 and 5.6, respectively. Moreover, a unique heterojunction structure of semi-metal/semiconductor/insulator can be directly formed in a single layer of graphene using a one-step fluorination process by introducing a Au thin-film as a buffer layer. With this heterojunction structure, it would be possible to fabricate transistors in a single graphene film via a one-step fluorination process, in which pristine graphene, partial F-graphene, and highly F-graphene serve as the source/drain contacts, the channel, and the channel isolation in a transistor, respectively. The demonstrated graphene transistor exhibits an on-off ratio above 10, which is 3-fold higher than that of devices made from pristine graphene. This efficient transistor fabrication method produces electrical heterojunctions of graphene over a large area and with selective patterning, providing the potential for the integration of electronics down to the single atomic-layer scale.

Surface Chemical Modification of Carbon Nanowalls for Wide-Range Control of Surface Wettability

Carbon nanowalls (CNWs) are self-assembled, free-standing, few-layered graphenenano-structures with large surface area, and thin graphene edges. For their application to nanobiotechnology, the effects of chemisorbed species on surface wettability were investigated. The surfaces of as-grown CNWs obtained using CH4/H2 mixture were hydrophilic. After Ar atmospheric pressure plasma treatments for up to 30 s, the contact angles of water droplets on the CNWs decreased from 51° to 5°, owing to a result of oxidation only at edges and surface defects. They increased up to 147° by CF4 plasma treatment at low pressure. The wide-range control of surface wettability of CNWs was realized by post-growth plasma treatments. We also demonstrated detection of bovine serum albumin using surface-modified CNWs as electrodes.

Enhancement-Mode LaLuO3–AlGaN/GaN Metal–Insulator–Semiconductor High-Electron-Mobility Transistors Using Fluorine Plasma Ion Implantation

In this work, enhancement-mode (E-mode) AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) with high-κ LaLuO3 (LLO) gate dielectric were fabricated by deploying the CF4 plasma treatment technique in a gate-dielectric-first planar process. CF4 plasma treatment can shift the threshold voltage from -2.3 V [for depletion-mode (D-mode) LLO MIS-HEMTs] to 0.6 V (for E-mode LLO MIS-HEMTs). Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) results suggest that fluorine ions could penetrate through the polycrystalline/amorphous LLO film and be implanted into the (Al)GaN barrier layer. The primary threshold voltage (VTH) shift mechanism of the E-mode LLO MIS-HEMTs is the negatively-charged fluorine ions in (Al)GaN, while fluorine atoms form chemical bonds with La/Lu atoms in the fluorinated LLO film. The E-mode LLO MIS-HEMTs exhibit a drive drain current density of 352 mA/mm at VGS = 2.5 V and a peak transconductance (Gm) of ∼193 mS/mm. Significant suppression of current collapse and low dynamic ON-resistance are obtained in the E-mode LLO MIS-HEMTs under high-drain-bias switching conditions.

Enhancement of Open-circuit Voltage Using CF4 Plasma Treatment on Nitric Acid Oxides

Surface passivation of solar cells is investigated using CF4 plasma treatment on low-temperature oxides to enhance the open-circuit voltage of the solar cells. Low-temperature oxides grown by a nitric acid solution are treated with the CF4 plasma. Solar cells undergoing this scheme show an improved performance, including low-saturation current density and good quantum efficiency at short wavelengths. Experimental results demonstrate that the CF4 plasma pretreatment on low-temperature oxides can significantly improve the open-circuit voltage, short-circuit current, and fill factor for silicon wafer-based solar cells. This technique is very promising for in-line solar cell manufacturing.

Superhydrophobic Transparent Surface of Nanostructured Poly(Methyl Methacrylate) Enhanced by a Hydrolysis Reaction

AbstractWe report a method to create a self‐cleaning, transparent surface on poly(methyl methacrylate) (PMMA) using a dry etching with CF4 plasma and a subsequent hydrolysis process with water immersion. During the CF4 plasma treatment, nanoscale pillar structures were formed and its aspect ratio tended to increase. However, the transparency was reduced due to the deposition and the accumulation of undesired capping layers, which cover the structures. The hydrolysis was used to remove the capping layers of metal fluoride. As a result, the surface improves their clarity based on the transmittance up to 95%, because the reflectivity was reduced. With a subsequent hydrophobic coating, a superhydrophobic surface was achieved showing robust anti‐wetting and anti‐dewing effects.magnified image

Improving Electrical Properties of Bottom-Gate Poly(3-Hexylthiophene) Thin-Film Transistor Using $\hbox{CF}_{4}$ Plasma Treatment

In this letter, the effect of CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> plasma treatment on poly(3-hexylthiophene)-based organic thin-film transistors has been investigated. It was found that CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> plasma treatment on the source/drain electrode can reduce contact resistance and increase mobility. The CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> plasma treatment can increase the mobility from 0.0021 to 0.0102 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V·s and decrease the contact resistance by about 70%. Moreover, the CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> plasma treatment is compatible with the bottom-gate bottom-contact structure without degrading the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer.

Characterization of gadolinium oxide thin films with CF4 plasma treatment for resistive switching memory applications

The effect of the CF4 plasma treatment on the gadolinium oxide (GdxOy) thin films for the resistive random access memory (RRAM) applications was investigated. The material properties of the fluorine incorporated GdxOy films were analyzed by the X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and ultraviolet–visible spectroscopy (UV–VIS). Further, the set and reset voltages of the Pt/GdxOy/W RRAM devices with the CF4 plasma treatment were effectively reduced to −1.15 and 2.1V respectively owing to the low Schottky barrier height. The formation of GdF bonds can prevent the oxygen atoms from out-diffusing through Pt grain boundaries into the atmosphere, leading to the superior retention characteristics for over 104s. The CF4 plasma treated GdxOy RRAMs can sustain a resistance ratio of 102 for more than 800 times stable set/reset cycling, suitable for future low-voltage and high-performance nonvolatile memory operation.

Enhanced adhesion of osteoblastic cells on polystyrene films by independent control of surface topography and wettability

We independently controlled surface topography and wettability of polystyrene (PS) films by CF4 and oxygen plasma treatments, respectively, to evaluate the adhesion and proliferation of human fetal osteoblastic (hFOB) cells on the films. Among the CF4 plasma-treated PS films with the average surface roughness ranging from 0.9 to 70nm, the highest adhesion of hFOB cells was observed on a PS film with roughness of ~11nm. When this film was additionally treated by oxygen plasma to provide a hydrophilic surface with a contact angle less than 10°, the proliferation of bone-forming cell was further enhanced. Thus, the plasma-based independent modification of PS film into an optimum nanotexture for human osteoblast cells could be appplied to materials used in bone tissue engineering.

Wettability and optical properties of O2 and CF4 plasma treated biaxially oriented semicrystalline poly(ethylene terephthalate) films

Influence of low pressure O2, CF4, and successive O2 and CF4 RF plasma treatment on optical properties and wettability of biaxially oriented semicrystalline poly(ethylene terephthalate) (PET) was examined. Produced by industrial stretch-blow molding PET films of the 300μm thickness were chosen for the experiments. Influence of the aging was also investigated by storing plasma treated samples at room conditions for 60 days. It was revealed that O2 plasma treated samples suffered from the hydrophobic recovery and long term improvement of hydrophilicity was only a moderate. Energetic CF4 plasma treatment was able to form a large number of surface active sites which in turn was capable to attach the oxygen containing groups and to increase the hydrophilicity. However, aged for 10–60 days CF4 plasma treated PET films have showed a large scattering of the contact angle values measured on the same surface. Successive O2 and CF4 plasma treatment, despite induced hydrophobicity of as treated films, after 3 days of aging have resulted in highly homogeneous hydrophilic (Θ≈20°) surfaces which have retained their hydrophilicity for the entire period of investigation. Moreover, combined plasma treatment of PET films has not influenced significantly the transmission of visible light. So, such a treatment can be considered as beneficial for the production of highly homogeneous hydrophilic surfaces without significant influence on their optical properties.

Thinning and functionalization of few-layer graphene sheets by CF4 plasma treatment

Structural changes of few-layer graphene sheets induced by CF4 plasma treatment are studied by optical microscopy and Raman spectroscopy, together with theoretical simulation. Experimental results suggest a thickness reduction of few-layer graphene sheets subjected to prolonged CF4 plasma treatment while plasma treatment with short time only leads to fluorine functionalization on the surface layer by formation of covalent bonds. Raman spectra reveal an increase in disorder by physical disruption of the graphene lattice as well as functionalization during the plasma treatment. The F/CF3 adsorption and the lattice distortion produced are proved by theoretical simulation using density functional theory, which also predicts p-type doping and Dirac cone splitting in CF4 plasma-treated graphene sheets that may have potential in future graphene-based micro/nanodevices.PACS81.05.ue; 73.22.Pr; 52.40.Hf.

Increased chemical enhancement of Raman spectra for molecules adsorbed on fluorinated reduced graphene oxide

Fluorinated reduced graphene oxide (F-RGO) is prepared by CF4 plasma treatment of RGO. The fluorine (F) doping is confirmed by X-ray photoelectron spectroscopy and its content is directly related to the plasma exposure time. A modest p-doping effect of the fluorination is observed from the electrical measurements. It is found that the F-RGO is an even better substrate for surface enhanced Raman spectroscopy of molecules than RGO. The relative enhancement factor can be tuned by manipulating the F content in the F-RGO. The effect is attributed to the presence of the strong local electric field induced by the local dipoles of F-containing groups on the F-RGO surface. This shows that the formation of well-designed surface dipoles could be a general way to increase the chemical enhancement of molecular Raman spectra.

Effect of O2, Ar/H2 and CF4 plasma treatments on the structural and dielectric properties of parylene-C thin films

Plasma treatment of parylene-C surfaces not only causes structural modification of the surface during the plasma exposure, but also leaves active sites on the surfaces, which decreases the dielectric properties. In this work, the effects of oxygen, argon/hydrogen and fluorine plasma treatment on the surface and dielectric properties of parylene-C thin films were investigated using Fourier transform-IR spectroscopy, energy dispersive x-ray analysis and dielectric spectroscopy measurement. The results showed that the plasma treatment successfully introduced fluorine functional groups and decreased the oxygen content on the parylene-C surfaces. It appears that the replacement of oxygen and hydrogen by fluorine atoms led to a decrease in the local orientational polarizability of parylene-C. Consequently, it was found that the atmospheric fluorine plasma-treated parylene-C possessed lower dielectric characteristics, 16% lower than the untreated parylene-C at industrial frequencies (10–104 Hz). The Ar/H2 plasma treatment is also an experimental means to reduce the dielectric properties and to decrease the oxygen content in parylene-C. In contrast, the oxygen plasma increases the dielectric constant and can cause deterioration of the leakage current associated with carbon depletion showing C–O and C=O formation. CF4 and Ar/H2 plasma treatment does not significantly affect the long molecular motion (α-relaxation). Additional extrinsic oxygen content due to O2 plasma treatment in the parylene-C structure reproduces the increase in the time constant of both the short (β-relaxation) and long molecular motion.

Ta2O5 Polycrystalline Silicon Capacitors with CF4 Plasma Treatment

In this research, the effects of CF4 plasma treatment with post annealing on the electrical characteristics and material properties of Ta2O5 dielectrics were determined. The dielectric performance characteristics of samples under different treatment conditions were measured using equivalent oxide thickness (EOT), current density–electric field (J–E) characteristics, gate voltage shift versus time, and Weibull plots. In addition, X-ray diffraction (XRD) analysis provided insight into the changes in crystalline structure, atomic force microscopy (AFM) measurements visualized the surface roughness, and secondary ion mass spectroscopy (SIMS) revealed the distribution of fluorine ions inside the dielectric samples. Findings indicate that dielectric performance can be significantly improved by CF4 plasma treatment for 1 min with post annealing at 800 °C. The improvements in electrical characteristics were caused by the appropriate incorporation of the fluorine atoms and the removal of the dangling bonds and traps. The Ta2O5 dielectric incorporated with appropriate CF4 plasma and annealing treatments shows great promise for future generation of nonvolatile memory applications.