CF4 Plasma Etching Research Articles

Effect of YF3 on fluorocarbon plasma resistance of Y2O3–Al2O3–B2O3 glasses

In this study, alumino-borate glass was manufactured to fabricate glass with excellent corrosion resistance to plasma, and the Y2O3 was substituted with YF3. The basic properties of the glass were analyzed DTA, density, hardness, and transmittance. Plasma corrosion resistance is evaluated by the etch rate, surface roughness, and XPS of the glasses via CF4 plasma etching. The results revealed that all glasses had superior plasma resistance than the reference material, quartz. As the amount of Y2O3 increased, the etch rate decreased, and the YF3-containing glasses exhibited the highest plasma resistance by an etch rate of 22.17 nm/min.

The influence of nanostructure on the wetting transition of polyvinylidene fluoride nanoweb: from the petal effect to the lotus effect

In this study, the effects of the surface structure of electrospun polyvinylidene fluoride (PVDF) nanoweb on surface wettability were analyzed. The conditions of the surface structure representing the lotus and petal effects were derived, and the difference in the dynamic behavior of the water droplets on the surfaces was investigated. To this end, a PVDF nanoweb was fabricated by electrospinning various concentrations of PVDF solutions. The nanoscale roughness was adjusted by varying the CF4 plasma etching time. It was seen that when the concentration of the electrospun PVDF solution was 15 or 20 wt%, a hierarchical structure of microbeads and nanofibers was formed. In the 20 wt% nanoweb, droplets formed an apparent contact angle of 149.5 ± 2.2°, and the petal effect was observed in which the droplets were pinned on the surface and did not roll off even when the nanoweb was tilted by 180°. As a result of introducing fine nanostructures with CF4 plasma etching on the 20 wt% nanoweb, the apparent contact angle increased to 162.8–164.4°, and the shedding angle decreased to 5.3–8.1°, showing a wetting transition to the lotus effect, regardless of the plasma etching time. In addition, the lotus effect was observed when 15 wt% nanoweb was treated with CF4 plasma etching for more than 10 min. We confirmed that the lotus effect was exhibited when the three-phase contact line of the PVDF nanoweb/water/air was discontinuous, and the contact area between the surface and the water droplets was reduced with increased air pockets at this interface, which led to a decrease in the adhesive force and the impact of negative pressure.

Silver film etching using halogen gas plasma

Silver (Ag) film etching was studied with a focus on suppressing the surface roughness induced by Cl2 and CF4 plasmas. After Cl2 plasma etching, roughening of the Ag surface was observed. From in situ x-ray photoelectron spectroscopy and atomic force microscopy analyses using a plasma beam system, the Ag surface was roughened with AgCl formation after Cl2 plasma treatment before exposure to air. In capacitively coupled Cl2 plasma, it seemed that many voids were formed on the Ag surface at a high bias power and cathode temperature. This was considered to be characteristic of agglomeration. In contrast, severe surface roughness was not observed after CF4 plasma etching, even at a high bias power and cathode temperature. Secondary ion mass spectrometry analysis showed high chlorine accumulation near the Ag film surface after Cl2 plasma etching. Possible agglomeration of the Ag film during Cl2 plasma etching was volume expansion caused by chlorine accumulation assumed to enhance the compressive stress of the Ag film, and this resulted in increased boundary grooving and, finally, agglomeration. In contrast, fluorine accumulation was unlikely during CF4 plasma etching, resulting in less Ag film stress, which suppressed grain boundary grooving and agglomeration.

Investigation of the formation mechanism of the fluorocarbon film in CF4 plasma processing of fused silica

In this work, the formation mechanism of the fluorocarbon film in CF4 plasma etching of fused silica has been explored. The chemical characteristics of the film were analyzed by x-ray photoelectron spectroscopy (XPS). In addition, the formation mechanism of surface deposition film was analyzed based on the chemical composition of surface film and emitting species of CF4 plasma. The roles of gas-phase excited, especially F atoms and CF2 radicals, were examined by optical emission spectroscopy (OES) as they contribute to SiO2 etching and fluorocarbon film formation respectively. Moreover, the effect of addition O2 on chemical reactions were investigated, the OES measurement and XPS analysis were compared between CF4 and O2/CF4 plasma processed. And the optical transmittance with different O2/CF4 ratios was carried out by ultraviolet-visible-near infrared (UV–vis-NIR) spectrometer to confirm the effect of O2 on inhibition of fluorocarbon film.

Highly selective SiO2 etching over Si3N4 using a cyclic process with BCl3 and fluorocarbon gas chemistries

A cyclic process for highly selective SiO2 etching with atomic-scale precision over Si3N4 was developed by using BCl3 and fluorocarbon gas chemistries. This process consists of two alternately performed steps: a deposition step using BCl3 mixed-gas plasma and an etching step using CF4/Ar mixed-gas plasma. The mechanism of the cyclic process was investigated by analyzing the surface chemistry at each step. BClx layers formed on both SiO2 and Si3N4 surfaces in the deposition step. Early in the etching step, the deposited BClx layers reacted with CFx radicals by forming CClx and BFx. Then, fluorocarbon films were deposited on both surfaces in the etching step. We found that the BClx layers formed in the deposition step enhanced the formation of the fluorocarbon films in the CF4 plasma etching step. In addition, because F radicals that radiated from the CF4 plasma reacted with B atoms while passing through the BClx layers, the BClx layers protected the Si3N4 surface from F-radical etching. The deposited layers, which contained the BClx, CClx, and CFx components, became thinner on SiO2 than on Si3N4, which promoted the ion-assisted etching of SiO2. This is because the BClx component had a high reactivity with SiO2, and the CFx component was consumed by the etching reaction with SiO2.

The Recessed Trapezoidal Groove Dual‐Gate AlGaN/GaN E‐Mode Transistor by Using Depletion Enhancement Effect

The recessed trapezoidal groove dual‐gate profile is achieved by the low power CF4 plasma etching based on the principle of ion‐scattering. The recessed trapezoidal groove dual‐gate architecture can increase the lateral broadening of depletion width, yielding the Enhancement‐mode operation. This device demonstrates a threshold voltage of 0.43 V, a maximum drain current of 480 mA mm−1 and a trans‐conductance of 308 mS mm−1. The device exhibits a low off‐state leakage current of ≈10−10 A mm−1 and gate induced drain leakage is effectively improved. An extrinsic current gain cut off frequency of 32 GHz and a maximum oscillation frequency of 65 GHz are deduced. The threshold voltage (Vth) stability of the Schottky gate HEMT is investigated. The recessed trapezoidal groove dual‐gate exhibits a small shift of Vth, which is attributed to the lateral extension of depletion region in the trapezoidal groove dual‐gate structure.

Superhydrophobic and antireflective surface of nanostructures fabricated by CF4 plasma etching

In this research, the nanostructured patterns were fabricated by the CF4 plasma etching process on the SiO2-based substrates, and treated with the Teflon coatings for superhydrophobicity and antireflection. First, the nickel thin films were deposited on the substrates by the PVD sputtering process at various deposition times. The prepared thin films underwent the rapid thermal annealing at 500 °C in order to promote the agglomeration of the nickel nanoparticulate patterns, which acted as the etch-resistant masks. These patterned substrates were consequently etched by the CF4 plasma. After the etching process, the nickel masks were removed by the nitric acid rinse. Subsequently, the polytetrafluoroethylene films were coated on the nanostructured surface in order to achieve the superhydrophobic properties. The samples were characterized by the field-emission scanning electron microscopy (FESEM), UV-Vis-NIR spectroscopy, and the contact angle measurements to study the physical morphologies, optical transmission spectra, and wettability of water for each sample condition. The results showed that the roughness of the etched surface greatly affected the variations of the superhydrophobic properties, and the antireflective surfaces. The developed nanostructured patterns were highly potential for several applications in optoelectronic and solar energy materials.

Patterning of wettability using the photocatalytic decomposition of hydrophobic self-assembled monolayer on the TiO2 pattern

We report a patterning process for an octadecylphosphonic acid self-assembled monolayer (ODP-SAM) using TiO2 patterns fabricated by a combined use of reactive sputtering and CF4 plasma etching. The ODP-SAM with the remaining outer region of TiO2 patterns can be used as a constant hydrophobic region. The photocatalytic decomposition of the ODP-SAM on TiO2 thin films can be applied to the formation of hydrophobic/hydrophilic wettability patterns. The photoresponsive wettability of TiO2 thin films with different surface morphologies was examined on films deposited under different sputtering conditions. The contact angle on the ODP-SAM/TiO2 surface was successfully changed from 134.8 to 0° by exposing the raw TiO2 surface after the photodecomposition of the ODP-SAM, whereas the contact angle on the ODP-SAM in the outer region of TiO2 patterns remained constant at 112.1°. The width of the wettability switching range of the raw surface of sputter-deposited TiO2 thin films can be controlled by changing the deposition conditions of the TiO2 thin films. Droplet generation solely through the bottom surface with wettability patterns defined by a combined use of an ODP-SAM and TiO2 patterns in a microchannel was also demonstrated.

AlGaN surfaces etched by CF4 plasma with and without the assistance of near-ultraviolet irradiation

Al0.24Ga0.76N thin film surfaces were etched with CF4 plasma, with and without the assistance of near-ultraviolet (UV) irradiation. The near-UV source was a black light lamp, which emitted wavelengths of 300–400 nm. The chemical compositions and morphologies of surfaces etched under the two plasma conditions were compared, to clarify the effect of near-UV irradiation on the properties of the AlGaN surface. Near-UV irradiation during CF4 plasma etching reduced the amounts of F atoms, AlFx fluorides, and GaFx fluorides incorporated into the surface, and enhanced the amount of CFx fluorocarbons. Near-UV irradiation did not influence the depth distribution of incorporated fluorine-related impurities, or the degree of nitrogen deficiency caused in the surface. These compositional changes in the surface occurred irrespective of the gas pressure. Near-UV irradiation caused a significant change in the morphology of surfaces etched at high gas pressure (13 Pa), as the etching time was increased to 60 and 100 min. Near-UV irradiation did not change the morphologies of surfaces etched at lower gas pressures (1.3 and 6.7 Pa), irrespective of etching time.

TiO2 patterns with wide photo-induced wettability change by a combination of reactive sputtering process and surface modification in a microfluidic channel

This paper reports the formation of TiO2 patterns with a wide range of photo-induced wettability switching from high hydrophobic to superhydrophilic states for on-chip liquid manipulation. TiO2 thin films with rough surface morphology were formed by a combination of optimised reactive sputtering and CF4 plasma etching. Octadecylphosphonic acid self-assembled monolayer (ODP-SAM) surface modification was applied to the surface-roughened TiO2 thin films in order to obtain a highly hydrophobic surface initially. Photocatalytic decomposition of ODP-SAM on the surface-roughened TiO2 by ultraviolet (UV) irradiation caused a wetting transition from the Cassie–Baxter state to the Wenzel state. Switching of the flow direction into branch channels was also demonstrated by utilising the photoresponsive wettability of the surface-modified TiO2 patterns on a fluidic chip.

An XRD Phase Analysis of Al-F Re-Deposition Produced from Reactive Ion Etching

This paper reports the analysis of the composition, structure and phase of the re-deposition material that was generated from the reaction from CF4 plasma etching on the Al2O3-TiC substrate. The re-deposition was sputtered from the etching area and deposited on a silicon coupon for analysis. The morphology of the re-deposition was investigated by scanning electron microscope (SEM) and the composite element of the re-deposition was detected by using energy dispersive x-ray spectroscopy (SEM-EDX). X-ray diffraction (XRD) was used to analyse the structure and phase of the re-deposition. The results show that the prepared re-deposition was composed of F and Al atoms, with 51.24 At% and 27.67 At%, respectively. XRD revealed that this was owing to the chemical formula AlF3, which has a rhombohedral crystal structure in the most stable alpha phase (α-AlF3).

Comparison between AlGaN surfaces etched by carbon tetrafluoride and argon plasmas: Effect of the fluorine impurities incorporated in the surface

Compositional and morphological changes in Al0.24Ga0.76N surfaces etched by CF4 and Ar plasmas were investigated in order to clarify the effect of fluorine impurities incorporated in the surface by the CF4 plasma. The CF4 plasma effectively incorporated the fluorine impurities in the surface even at a short etching time. A small number of the incorporated fluorine impurities only contributed to the formations of Al(OH)xFy and GaFx on the surface even as the etching time increased. Although the CF4 and Ar plasma etchings preferentially remove nitrogen atoms from the surfaces, the preferential removal induced by the CF4 plasma etching was suppressed compared with the case of the Ar plasma etching. The CF4 plasma etching caused a smooth surface regardless of the gas pressure and the etching time, whereas the Ar plasma etching changed the surface morphology depending on the gas pressure and the etching time. The incorporation of the fluorine impurities, which bonded with the cation vacancies such as gallium and aluminum vacancies introduced in the surface by the plasma etching, was considered to concern the suppression of the preferential removal and the formation of the smooth surface.

Extreme wettability of nanostructured glass fabricated by non-lithographic, anisotropic etching.

Functional glass surfaces with the properties of superhydrophobicity/or superhydrohydrophilicity, anti-condensation or low reflectance require nano- or micro-scale roughness, which is difficult to fabricate directly on glass surfaces. Here, we report a novel non-lithographic method for the fabrication of nanostructures on glass; this method introduces a sacrificial SiO2 layer for anisotropic plasma etching. The first step was to form nanopillars on SiO2 layer-coated glass by using preferential CF4 plasma etching. With continuous plasma etching, the SiO2 pillars become etch-resistant masks on the glass; thus, the glass regions covered by the SiO2 pillars are etched slowly, and the regions with no SiO2 pillars are etched rapidly, resulting in nanopatterned glass. The glass surface that is etched with CF4 plasma becomes superhydrophilic because of its high surface energy, as well as its nano-scale roughness and high aspect ratio. Upon applying a subsequent hydrophobic coating to the nanostructured glass, a superhydrophobic surface was achieved. The light transmission of the glass was relatively unaffected by the nanostructures, whereas the reflectance was significantly reduced by the increase in nanopattern roughness on the glass.

A tunable sub-100 nm silicon nanopore array with an AAO membrane mask: reducing unwanted surface etching by introducing a PMMA interlayer.

Highly ordered silicon (Si) nanopores with a tunable sub-100 nm diameter were fabricated by a CF4 plasma etching process using an anodic aluminum oxide (AAO) membrane as an etching mask. To enhance the conformal contact of the AAO membrane mask to the underlying Si substrate, poly(methyl methacrylate) (PMMA) was spin-coated on top of the Si substrate prior to the transfer of the AAO membrane. The AAO membrane mask was fabricated by two-step anodization and subsequent removal of the aluminum support and the barrier layer, which was then transferred to the PMMA-coated Si substrate. Contact printing was performed on the sample with a pressure of 50 psi and a temperature of 120 °C to make a conformal contact of the AAO membrane mask to the Si substrate. The CF4 plasma etching was conducted to transfer nanopores onto the Si substrate through the PMMA interlayer. The introduced PMMA interlayer prevented unwanted surface etching of the Si substrate by eliminating the etching ions and radicals bouncing at the gap between the mask and the substrate, resulting in a smooth Si nanopore array.

Optimization of Reverse Engineering Processes for Cu Interconnected Devices

Reverse engineering of semiconductor devices utilizes delayering processes, in order to identify how the interconnection lines are stacked over transistor gates. Cu metal has been used in recent fabrication technologies, and de-processes becomes more difficult with the shrinking device dimensions. In this article, reverse engineering technologies to reveal the Cu interconnection lines and Cu via-plugs embedded in dielectric layers are investigated. Stacked dielectric layers are removed by CF4 plasma etching, then the exposed planar Cu metal lines and via-plugs are selectively delineated by wet chemical solution, instead of the commonly used plasma-based dry etch. As a result, we have been successful in extracting the layouts of multiple layers within a system IC, and this technique can be applicable to other logic IC, analog IC, and CMOS IC, etc.

Atomic layer etching removal of damaged layers in a contact hole for low sheet resistance

A damaged layer remains on silicon substrates after high-aspect-ratio contact (HARC) etching when using a fluorocarbon gas. Atomic layer etching (ALET) is a technique that can be applied to remove the damaged layer of silicon, removing about 1.36 Å per etch cycle. The characteristics of contact damage removal by ALET are investigated and compared with the conventional damage removal technique of low-power CF4 plasma etching. The low-power CF4 plasma etching technique not only has inadequate etch depth control, but also introduces secondary damage by implanting impurities about 25 Å into the contact bottom of the silicon surface. However, ALET allows contact damage to be removed effectively without introducing secondary damage to the substrate, and with precision etch depth control at the angstrom scale. When ALET is applied subsequent to low-power CF4 plasma etching, the fluorine- and carbon-damaged silicon is effectively removed in about 10 cycles. The sheet resistance of HARC etched silicon decreases from 142 to 137 Ω/◻ after using low-power CF4 plasma etching, and subsequent ALET treatment further decreases the sheet resistance to 129 Ω/◻, which is close to the reference value of 124 Ω/◻.

Hierarchical structures of AlOOH nanoflakes nested on Si nanopillars with anti-reflectance and superhydrophobicity

A novel method to fabricate ultra-low reflective Si surfaces with nanoscale hierarchical structures is developed by the combination of AlOOH or boehmite nanoflakes nested on plasma-etched Si nanopillars. Using CF4 plasma etching, Si surfaces are nanostructured with pillar-like structures by selective etching with self-masking by fluorocarbon residues. AlOOH nanoflakes are formed by Al thin film coating with various thicknesses and subsequent immersion in boiling water, which induces the formation of nanoscale flakes through the hydrolysis reaction. AlOOH nanoflakes are formed on Si nanopillared surfaces for hierarchical structures, which are coated with a low-surface-energy material, resulting in a higher water wetting angle of over 150° and a very low contact angle hysteresis of less than 5°, and implying a self-cleaning surface. Reflectance reduced to 5.18% on average on hierarchical nanostructures in comparison to 9.63% on the Si nanopillar surfaces only. We found that Si nanopillars reduced reflection for wavelengths ranging from 200 to 1200 nm while AlOOH nanoflakes reduced reflection for wavelengths longer than 600 nm.

A multilayer approach for enhancing the erosive wear resistance of CVD diamond coatings

The erosive wear behavior of mono-, bi- and multilayered diamond composite coatings grown by hot filament chemical vapor deposition (HFCVD) is investigated. The effect of the surface pre-treatment on the silicon nitride substrates was firstly evaluated revealing that flat lapping mechanical treatment combined with chemical CF4 plasma etching is the best surface preparation to achieve high adhesion levels. Multilayers were designed to combine the excellent adhesion of microcrystalline diamond (MCD) with a top nanocrystalline diamond (NCD) layer of reduced surface roughness. Indeed, the multilayered diamond coatings revealed the best erosive resistance, whose damage occurred by gradual loosening of material from the outer layer after longer testing time. The absence of areas with film spallation or substrate exposure is given by the action of the MCD/NCD interfaces in deflecting cracks, thus acting as “energy sinks” to further propagation. An analytical model of the stress field distribution within the coatings based on the von Mises criterion was developed to elucidate the erosive mechanical behavior of the different diamond composites.

Photocatalytic thin Films Prepared by Plasma Curing of Non‐Reactive Siloxane Dispersions Containing TiO2 Particles

AbstractPhotocatalytic TiO2 layers prepared by PVD or CVD processes are already produced industrially. The deposited TiO2 needs a sufficiently high concentration of the photocatalytically active anatase phase which is produced at higher substrate temperature. As a consequence, the PVD/CVD techniques are limited to heat‐resistant substrates. A novel approach for plasma hybrid coating technology is presented here using the advantages of a cold low‐pressure plasma process in combination with non‐reactive siloxane (polydimethylsiloxane – PDMS) dispersions containing sub‐micron TiO2 particles for surface functionalisation. As the result, a mechanically stable composite film containing TiO2 particles with a diameter of up to several times the average coating thickness is generated. The film consists of a top SiO2‐like surface layer and, depending on the initial film thickness, an underlying gradually demethylated and crosslinked siloxane. Although the TiO2 particles are partially covered by a thin matrix layer of several nanometres, the thin coating shows photocatalytic activity as demonstrated by UV‐degradation of methylene blue. The photocatalytic activity depends on the TiO2 particle concentration in the film and can be further enhanced by exposing the TiO2 surface by CF4 plasma etching of the composite film (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Plasma chemical behaviour of reactants and reaction products during inductively coupled CF4 plasma etching of SiO2

A two-dimensional fluid model has been developed to study plasma chemical behaviour of etch products as well as reactants during inductively coupled CF4 plasma etching of SiO2. The plasma fluid model consisted of Maxwell's equations, continuity equations for neutral and charged species including gas-phase and surface reactions and an energy balance equation for electrons. The surface reaction model assumed Langmuir adsorption kinetics with the coverage of fluorine atoms, fluorocarbon radicals and polymers on SiO2 surfaces. Numerical results indicated that etch product species occupy a significant fraction of reactive ions as well as neutrals in the reactor chamber during etching, which in turn leads to a change in plasma and surface chemistry underlying the processing. In practice, the density of SiF4 was typically about 10% of that of the feedstock CF4, being comparable to that of the most abundant fluorocarbon radical CF2; moreover, the density of was typically about 5% of that of the most abundant fluorocarbon ion . The density and the distribution of such product species in the reactor chamber were changed by varying the ion bombardment energy on the substrate surfaces, gas pressure, mass flow rate and coil configuration, which arises in part from gas-phase reactions depending on plasma electron density and temperature. Surface reactions on the chamber walls and on the substrate also affect the product density and distribution in the reactor; in particular, the surface reactions on the SiO2 dielectric window as well as substrate surfaces were found to largely affect the product density and distribution.