Fluorine Plasmas Research Articles

Surface modification of white PVC polymer by different plasma immersion techniques

Polymer substrates have several distinct advantages, such as, robustness, low density, impact resistance, and conformity over glass substrates for optical applications. Some applications are impeded, however, owing to its low adhesion to thin films, surface roughness, and low gas permeability. In this work, the wettability and the surface morphology of Poly(Vinyl) Chloride, PVC, samples were modified by plasma immersion. PVC was chosen because of its already wide use and low cost: PVC is used in floor coverings, plumbing, electrical insulation, hoses, containers, and other accessories. In this work, plasma immersion was used to modify the chemical structure of white PVC, producing high values of contact angles (? > 100º) in fluorine plasmas, measured immediately after treatments, and until 30 days after. Also, it was detected low values of contact angles (? < 50º) in nitrogen plasmas. Atomic Force Microscopy revealed smooth surfaces, whose roughness, Rz, was less than ~13 nm, except for plasma immersion cathode, which yielded a Rz of ~213 nm.

Photovoltage Optimization of Si Devices with a Fluorinated Graphene Interfacial Layer

The photovoltage produced by a semiconductor device can be optimized by controlling the interfacial energetics, including the surface dipole and electric field. When a positive surface dipole is introduced to a p-type semiconductor surface, the band edges shift to increase the resulting barrier height in contact with a metal, which in turn improves the photovoltage of the device. To generate a positive surface dipole, highly electronegative moieties must be attached to create a layer of negatively charged species close to the surface. While numerous methods have been developed to modify semiconductor surfaces for control over surface dipole and electric field at the interface, introducing highly electronegative moieties like fluorine atoms directly to the surface is very difficult due to the lack of appropriate synthetic methods. Most fluorinating agents that could introduce fluorine atoms directly to a silicon surface instead etch the silicon (i.e. hydrofluoric acid, xenon difluoride, fluorine plasmas). Indirect modifications are also difficult as fluorocarbon-based nucleophiles are transient and decompose quickly in solution. This work demonstrates that a positive C-F dipole can be introduced to tune the band edges of p-type silicon (p-Si) by placing a monolayer of fluorinated graphene (F–Gr) at the interface of a semiconductor and metal. The barrier heights of bare, hydride-terminated p-Si electrodes coated a layer of platinum (Pt, ~100 nm) were measured using solid-state current-voltage measurements and impedance spectroscopy. These electrodes demonstrated ohmic behavior as expected given the work function of Pt. In comparison, identical electrodes with an interstitial layer of F–Gr demonstrated rectifying behavior and improved barrier heights, controlled by the degree of fluorination of the Gr basal plane. X-ray photoelectron spectroscopy indicated that the formation of Pt silicide at the interface was attenuated by the presence of the monolayer of F–Gr even after stress testing at high temperature. Additionally, these electrodes were tested for hydrogen evolution activity to demonstrate their viability for use in a solar fuels device. F–Gr shows promise to maximize the efficiency of a solar fuels device by favorably tuning the band edges of semiconductor surfaces.

Study of wettability and optical transparency of pet polymer modified by plasma immersion techniques

Polymers substrates have several distinct advantages, such as ruggedness, robustness, ultra-lightness, conformability, and impact resistance over glass substrates for optical applications. However, it is required high transparency, proper surface roughness, low gas permeability and high transparent electrode conductivity of the plastic substrate for commercial applications. In this work was analyzed the surface morphology of polymer samples modified by plasma immersion techniques. Polyethylene Terephthalate (PET) polymers were treated by different RF plasma immersion modes (at low and high energy ion implantation) and discharge conditions. Sulfur hexafluoride (SF6) and nitrogen (N2) gases were employed as a source of fluorine and inert plasma, respectively. Wettability surface shows that, it is possible to reach either high or low contact angle values, (10o < ? < 130o), depending on the plasma technique and gas employed. The surface morphology was measured with atomic operating on air. Both 10 µm × 10 µm and 1 µm × 1 µm images were acquired and the surface roughness was characterized in terms of the root mean square roughness, Rz, for both imaged areas. In general, the smoothness of PET was maintained for some plasma treatments. Optical Transmittance, T (?), was performed using a UV-Vis-NIR spectrometer ranging from 190 nm to 3300 nm. The results show that the low energy ion implantation is more efficient to promote the loss of T (?) at visible light, making the PET surface hydrophilic, even in fluorine plasmas. The treatments were satisfactory, daring to maintain, or even, to increase the PET transparency at visible light in restrict conditions.

Inductively coupled plasma reactive-ion etching of β-Ga2O3: Comprehensive investigation of plasma chemistry and temperature

The authors investigated the inductively coupled plasma reactive-ion etching (ICP-RIE) of β-Ga2O3 using different fluorine and chlorine-based plasmas. Sn-doped (-201) oriented β-Ga2O3 substrates were etched using SF6/Ar, CHF3/Ar, O2/Ar, BCl3/Ar, and Cl2/Ar based ICP-RIE. Appreciable etch rates were obtained only with chlorine and boron-trichloride based plasmas, and the authors performed a comprehensive study on the composition and temperature-dependence of ICP-RIE of β-Ga2O3 in BCl3/Cl2/Ar plasmas in a temperature range of 22 to 205 °C. In general, the etch rate decreased with increasing Cl2 content in BCl3/Cl2/Ar plasmas. A high etch rate of 144 nm/min with a smooth surface morphology was obtained in BCl3/Ar plasmas, compared to 19 nm/min in Cl2/Ar plasmas. The etching behavior of Ga2O3 shows more similarity to that of Al2O3 than to that of GaN.

Reactive high power impulse magnetron sputtering of CFx thin films in mixed Ar/CF4 and Ar/C4F8 discharges

The reactive high power impulse magnetron sputtering processes of carbon in argon/tetrafluoromethane (CF4) and argon/octafluorocyclobutane (c-C4F8) have been characterized. Amorphous carbon fluoride (CFx) films were synthesized at deposition pressure and substrate temperature of 400mPa and 110°C, respectively. The CFx film composition was controlled in the range of 0.15<x<0.35 by varying the partial pressure of the F-containing gases from 0mPa to 110mPa. The reactive plasma was studied employing time averaged positive ion mass spectrometry and the resulting thin films were characterized regarding their composition, chemical bonding and microstructure as well as mechanical properties by elastic recoil detection analysis, X-ray photoelectron spectroscopy, transmission electron microscopy, nanoindentation, and water droplet contact angle measurements, respectively. The experimental results were compared to results obtained by first-principles calculations based on density functional theory. The modeling of the most abundant precursor fragment from the dissociation of CF4 and C4F8 provided their relative stability, abundance, and reactivity, thus permitting to evaluate the role of each precursor during film growth. Positive ion mass spectrometry of both fluorine plasmas shows an abundance of CF+, C+, CF2+, and CF3+ (in this order) as corroborated by first-principles calculations. Only CF3+ exceeded the Ar+ signal in a CF4 plasma. Two deposition regimes are found depending on the partial pressure of the fluorine-containing reactive gas, where films with fluorine contents below 24at.% exhibit a graphitic nature, whereas a polymeric structure applies to films with fluorine contents exceeding 27at.%. Moreover, abundant precursors in the plasma are correlated to the mechanical response of the different CFx thin films. The decreasing hardness with increasing fluorine content can be attributed to the abundance of CF3+ precursor species, weakening the carbon matrix.

Plasma etching dynamics of CaxBa1−xNb2O6 (CBN) material

► We study the plasma etching of the Ca x Ba 1− x Nb 2 O 6 in various gases for varying pressures and substrate temperatures. ► Etching at higher pressure increases the redeposition rate and therefore, surface inhibition decreases the etching yield. ► Etching with chlorine is purely physical between −75 and 375 °C in all the conditions. ► Etching with fluorinated gas is inhibited below 150 °C by adsorption of fluor species. ► Desorption of these fluorinated species occurs at higher temperature, removing the surface inhibition. This work reports an extensive study on the etching of Calcium Barium Niobate (CBN, a novel electro-optical material), using high density plasma processes. Different plasma chemistries (inert, chlorine and fluorine plasmas) are used to etch Ca 0.28 Ba 0.76 Nb 2 O 6 (CBN-28) thin films at pressures going from 1 to 10 mTorr, bias voltages going from 0 to 600 V and substrate temperatures ranging from −75 to 375 °C. For all the conditions investigated, the experimental data are compared with a simple sputtering model and completed with TOF-SIMS measurements of some of the samples processed. This study shows that there is no chemical enhancement or inhibition in the case of chlorinated plasma (Cl 2 ) regardless of the ion energy or the substrate temperature. In the case of an SF 6 -Ar plasma, it is shown that the observed increase of the etch yield above 150 °C results from a reduced inhibition as the temperature increases, this inhibition being caused by F and F 2 species adsorption at the surface of the material.

Controlled Chlorine Plasma Reaction for Noninvasive Graphene Doping

We investigated the chlorine plasma reaction with graphene and graphene nanoribbons and compared it with the hydrogen and fluorine plasma reactions. Unlike the rapid destruction of graphene by hydrogen and fluorine plasmas, much slower reaction kinetics between the chlorine plasma and graphene were observed, allowing for controlled chlorination. Electrical measurements on graphene sheets, graphene nanoribbons, and large graphene films grown by chemical vapor deposition showed p-type doping accompanied by a conductance increase, suggesting nondestructive doping via chlorination. Ab initio simulations were performed to rationalize the differences in fluorine, hydrogen, and chlorine functionalization of graphene.

Fluorine-doped SiO 2 and CF low- k dielectrics obtained during RIE process in fluorine plasmas

We have investigated the effect of silicon dioxide reactive ion etching (RIE) parameters and the type of plasma on the concentration of fluorine and its chemical compounds, such as CF, SiF and SiOF, in the polymer layer that is formed during this process on the top of etched layer, and their thermal stability. The polymeric layer formed on the etched surface appeared to consist of fluorine and silicon fluoride (CF, SiOF and SiF). The thickness and chemical composition of polymer layer formed on the etched surface depends on the type of used fluorine plasma (CF 4 or CHF 3). Low- k layer formed during RIE in CHF 3 plasma consists of CF, SiOF and SiF species, whose intensity and thickness depend on the etching process parameters. For CF 4 plasma, polymer layer consists of SiOF and SiF species, whose intensity and thickness depend also on the etching process parameters. However, only for CHF 3 plasma it is possible to control the etching/deposition process dynamically by the adequate adjusting process parameters. In contrast to the CF/SiOF/SiF layer formed during RIE in CHF 3 plasma, the SiOF/SiF ultra-thin layer is not thermally stable and its thickness is too low for the intermetal dielectric (IMD) application.

Investigation of sub-nm ALD aluminum oxide films by plasma assisted etch-through

A new technique, called “plasma defect etching” (PDE), is proposed for studying the continuity of ultra-thin layers. The PDE technique utilizes the extremely high selectivity in the deep reactive ion etching (DRIE) process, thus achieving visualization of the defects in the layer, because etching of substrate happens only through voids and microholes of the layer. The etch profile generally reproduces the non-continuous structure of the layer. This PDE technique was applied for the investigation of thin, sub-nm aluminum oxide films grown on silicon wafers by atomic layer deposition (ALD) technique. Silicon substrate was etched by SF 6 at cryogenic temperatures in an inductively coupled plasma (ICP) reactor, exploiting the extremely high ratio of silicon/aluminum oxide etch rates in fluorine plasmas. The surface morphology was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The PDE method shows that in the case of water as an oxidation precursor, separate islands of aluminum oxide form during the five first ALD cycles. On the other hand, the use of ozone precursor helps to oxidize silicon surface and facilitates growth of a uniform layer.

Inductively coupled plasma reactive ion etching of ZnO using C2F6 and NF3-based gas mixtures

Inductively coupled plasma reactive ion etching (ICP RIE) of ZnO film using C2F6 and NF3-based gas mixtures was investigated as a function of ICP power, bias power, pressure, and plasma chemistry. An etch rate of about 410 nm min−1 in the case of C2F6 plasma and about 380 nm min−1 in the case of NF3 plasma was obtained at the optimum condition, with vertical sidewalls and smooth surfaces, which is about 30% higher than the etch rates obtained in the previous reports on ICP RIE of ZnO using CH4 or chlorine-related gas mixtures. Basically no chamber contamination and corrosion was observed, indicating that fluorine plasmas are more suitable for ZnO dry etching than previously studied CH4 or BCl3 plasma. The addition of 40% or more CH4 to the C2F6 plasma improved the etch rate and sidewall verticality of the etched mesas, but resulted in rough surface morphology.

Photoresist etch resistance enhancement using novel polycarbocyclic derivatives as additives

In house synthesized mixed derivatives containing at least two carbocycles per molecule from the group of anthracenes, adamantanes and steroids with functionalized carbon chains are used as modifiers of resist properties and especially etch resistance enhancement and absorption characteristics. Etch resistance enhancement is demonstrated in oxygen, fluorine, and chlorine-containing plasmas under reactive ion etching and inductively coupled plasma etching conditions for poly(methyl-methacrylate) and a chemically amplified, positive-tone, methacrylate-based 193 nm photoresist formulation. High resolution experiments show that the proposed additives do not adversely affect the lithographic properties of the photoresists. The additive role is explained with empirical etch parameters such as the Ohnishi number and the ring parameter.

High-sensitivity, portable, tunable imaging X-ray spectrometer based on a spherical crystal and MCP

A portable (200×100×100 mm 3), high-luminosity, spherically bent crystal spectrometer was designed to measure very low emissivity X-ray spectra of different elements with spatial resolution in a wide spectral range (1.2−19.6 Å). A large (50×15 mm 2) open aperture mica spherically bent crystal with R=150 mm was used as dispersive and focusing element. This spectrometer was associated with a large sensitive area ( φ=40 mm) micro-channel plates assembly. This apparatus provides simultaneously high spectral ( λ/ δλ∼1800) and spatial (100–200 μm) resolutions. Its large tunability allowed, without any adjustment of the spectrometer set-up, to record spectra in the 1.38–17.5 Å wavelength range. We used the X-ray emission of femtosecond laser-produced plasmas from different materials ((CF 2) n , CaF 2, Cu, Al) to test the spectrometer. Thanks to the high sensitivity (high collection efficiency) of the system, high quality space-resolved X-ray spectra of Fluorine and Aluminum plasmas were obtained on a single laser shot.

Observation of ion-ion correlation effects on emissivity and opacity of hot ultra-dense low Z plasmas

The transmission function and the resulting emissivity and opacity of bound–bound transitions in hot ultra-dense, low Z (aluminum or fluorine) plasmas are investigated in this paper. It is shown that the treatment of both the area-normalized line profiles and the absorption oscillator strengths involved are crucial. Taking account, self-consistently, of all the interactions inside a radiating transient molecule, as proposed in the dicenter code IDEFIX, we computed the photo-excitation cross-sections, the emissivities, the opacities, and then compare the results with those from standard codes. We emphasize the strong dependence of the above quantities with the ionic correlations. A first experiment, devoted to measure opacities and emissivities of hot and ultra-dense aluminum plasmas, has been designed. The interpretation of the results shows the adaptability of the dicenter model for these extreme conditions.

Application of 4-methyl-1-acetoxycalix[6]arene resist to complementary metal–oxide–semiconductor gate processing

Gate lengths from 10 to 30 nm are beyond the reproducible limits of chemically amplified negative resists. Gate stack etching, the most challenging step, requires a negative, nonmetallic resist capable of withstanding enhanced etching with fluorine plasmas. This paper describes a new negative resist, 4-methyl-1-acetoxycalix[6]arene (MAC) which has demonstrated 10 nm scale resolution and etch resistance matching that of novolaks. Because increased etch resistance is required to allow reasonable resist aspect ratios, this work addresses techniques for increasing the etch resistance of MAC resist. The major disadvantage of MAC is its very low sensitivity; to address this we present a technique for combining the use of UVN with MAC.

Harmonic generation from ions in underdense aluminum and lithium–fluorine plasmas

High harmonic generation from laser interactions with preformed underdense plasmas was observed with subpicosecond ultraviolet laser pulses focused to intensities up to 1018 W/cm2. The generation of seventh and ninth harmonics from aluminum plasmas was measured as well as harmonics to the nineteenth order from lithium–fluorine plasmas. The harmonic generation efficiency measured in these experiments is less than that from previous experiments that used neutral gases.

Experimental exhibition of strongly correlated plasma effects. Asymmetrical line wings and possible transient molecule features

We report on the analysis of spatially resolved X-ray emission from the densest part of plasmas created by laser irradiation of plane targets. Because of the high electron densities and low temperatures involved, the plasmas are strongly correlated and not very emissive. We present a new experimental technique providing an extensive enhancement of the emission profiles and allowing the access to ultradense plasma regimes hitherto unobtainable. The broadening of F L β and Al L β lines is discussed with respect to asymmetries and the possible formation of transient molecules. An identification of the satellites exhibited is proposed and the presence of the ionic-molecule F 8+-F 9+ in highly correlated fluorine plasmas is suggested.

Intensity ratio of resonance lines as a diagnostic of initial conditions suitable for XUV laser action in recombining plasmas

The time varying ratio of intensities of resonance lines of H- and He-like ions in laser irradiated cylindrical fibre targets is analysed using a hydro/atomic physics code. Correspondence between the ratio and gain on the Balmer α transition of H-like ions in the adiabatically cooling and recombining plasma is found. The line ratios and absorbed energies corresponding to maximum gains for carbon, oxygen and fluorine plasmas are calculated. A useful diagnostic method is proposed for infering the absorbed energies in the plasmas and for monitoring the production of plasmas which should give maximum gain during adiabatic expansion.

X-ray photoelectron spectroscopy study of polymer surface reactions in F2 and O2 gases and plasmas

The surface kinetics of polystyrene, polyparaphenylene, and polyvinylmethylketone films in oxygen and fluorine plasmas was studied in a novel reactor which exposes a sample maintained in high vacuum to the species present in a plasma. These polymers were chosen as they contain the same chemical functional groups found in polymers currently used in the semiconductor industry. The reactor configuration enabled the determination of the surface composition using x-ray photoelectron spectrometry as a function of exposure time to the plasma species. The experimental data indicates that the initial reaction probability depends on the functional groups present in the polymer for both atomic oxygen and molecular fluorine attack. Molecular oxygen did not react with any polymers. Polymers containing aromatic functional groups reacted faster with the gas-phase species than polymers containing carbonyl groups. For the reaction of the polymers with an oxygen plasma, production of surface carbonyl and carboxylic acid groups was favored over the formation of surface alcohol species. For the reaction of the polymers with molecular fluorine, formation of surface CF1 species dominated in aromatic containing polymers. The dependence on the functional group was also evident at long reaction times. The effect was most prevalent for the reaction of molecular fluorine with the polymer samples, where the fluorine to carbon ratio for aromatic polymers was more than twice that of a carbonyl containing polymer. Fluorine plasmas were so reactive with all polymers that the effect of the polymer functional group could not be determined. The reaction of the polymers with a fluorine plasma resulted in the formation of surface CF2 species.

Studies of the reactive ion etching of SiGe alloys

Reactive-ion etching (RIE) of epitaxial, strained Si1−xGex alloys, x≤0.20, in fluorine-chlorine-, and bromine-based low-pressure plasmas has been investigated. The reactive-ion etch rates of the Si1−xGex alloys increase with the Ge content of the alloy for most etching gases. This effect is most pronounced for fluorine (CF4 and SF6) plasmas where the etch rate of a Si80Ge20 alloy is increased by a factor of ≂2 over that of Si. The etch rate enhancement is of reduced importance for chlorine (CF2Cl2) and bromine (HBr) plasmas, where the etch rate increases by less than 50% for a Si80Ge20 alloy relative to that of elemental Si. Analysis shows that the etch rate increase is not accounted for by the greater rate of gasification of Ge atoms alone but that the presence of Ge atoms in the SiGe alloy increases the Si etch product formation rate. Directional SiGe profiles are observed for CF2Cl2 and HBr plasmas which are identical to those obtained with Si. After etching in CF4 or SF6 plasmas the Ge surface concentration of the SiGe alloy is increased relative to its bulk value and both fluorinated Si and Ge are observed by in situ x-ray photoemission spectroscopy. On the other hand, for CF2Cl2 and HBr plasmas the SiGe surface is Si rich. The effect of band-gap narrowing, strain and plasma-induced surface modifications on the etching of the SiGe alloys is discussed.

Trench process with HBr chemistry in ripe

The RIPE (Resonant Inductive Plasma Etcher) uses inductively coupled radio frequency power to generate a high density plasma at low pressure. Its capabilities in fluorine plasmas have already been demonstrated [1]. To satisfy all basic requirement for pattern transfer, Hbr chemistry for trench and polysilicon etching has been tested in a pressure range1 to10 μbar. This work is related to the study of a trench process etch in HBr chemistry. Good profiles with high etch rate (0.7 μm/min) and high selectivity with respect to the SiO2 (12:1 to 100:1) are presented.